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Slurry sand content and concrete interaction in drilled shaft construction

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Title:
Slurry sand content and concrete interaction in drilled shaft construction
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Book
Language:
English
Creator:
Deese, Gregory Gene
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University of South Florida
Place of Publication:
Tampa, Fla.
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Subjects / Keywords:
bentonite
deep foundation
caisson
quality assurance
filter cake
Dissertations, Academic -- Civil Engineering -- Masters -- USF   ( lcsh )
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government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
ABSTRACT: Due to the widespread use of drilled shafts in state and federal highway bridges, strict regulation of the design and construction has been imposed by the respective agencies. However, documented cases of anomalies and/or poorly performing shafts continue to arise. To this end, this thesis investigates several aspects of drilled shaft construction that may affect the quality of the finished product. These areas include bentonite slurry properties and performance as well as reinforcement cage and concrete flow interactions. Recent research indicates tremie poured concrete does not flow as predicted. Instead of even rising, a differential between the height of concrete inside and outside the reinforcement cage has been observed.Compounding this problem is the fact that bentonite slurry used to support boreholes may settle suspended sand at the toe of the shaft or on the surface of rising concrete during long wait periods, affording the possibility of soil inclusions in the shaft. This thesis examines two methods of inquiry to quantify the behavior of concrete in a tremie pour drilled shaft and sand suspension behavior of bentonite slurry. Conclusions and recommendations are made to improve pertinent construction regulations to ensure quality of drilled shafts.
Thesis:
Thesis (M.S.C.E.)--University of South Florida, 2004.
Bibliography:
Includes bibliographical references.
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Mode of access: World Wide Web.
Statement of Responsibility:
by Gregory Gene Deese.
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Title from PDF of title page.
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Document formatted into pages; contains 116 pages.

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University of South Florida Library
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University of South Florida
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All applicable rights reserved by the source institution and holding location.
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aleph - 001498262
oclc - 57710722
notis - AJU6867
usfldc doi - E14-SFE0000500
usfldc handle - e14.500
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SFS0025191:00001


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Slurry Sand Content and Concrete Inte raction in Drilled Shaft Construction by Gregory Gene Deese A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering Department of Civil Engineeri ng and Environmental Engineering College of Engineering University of South Florida Major Professor: Austin Gray Mullins, Ph.D. Rajan Sen, Ph.D. Abla Zayed, Ph.D. Date of Approval: November 5, 2004 Keywords: bentonite, deep foundation, caiss on, quality assurance, filter cake Copyright 2004 Gregory G. Deese

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i Ta bl e o f C on ten ts L i s t o f T a b l e s .......................................................... iii L i s t o f F i g u r e s .......................................................... v A b s t r a c t .............................................................. ix 1 0 I n t r o d u c t i o n ......................................................... 1 2 0 L i t e r a t u r e R e v i e w .................................................... 5 2 1 H i s t o r i c a l B a c k g r o u n d .......................................... 5 2.2 Drilled Shaft Constr uction Met hods . . . . . . . . . . . . . . . . 7 2 2 1 D r y C o n s t r u c t i o n M e t h o d ................................ 7 2.2.2 W et (Slurr y Displacement) Construct ion Method . . . . . . . 8 2 2 3 C a s i n g C o n s t r u c t i o n M e t h o d .............................. 9 2 3 D r i l l i n g S l u r r y ................................................ 10 2 3 1 N a t u r a l S l u r r i e s ....................................... 10 2 3 2 M i n e r a l S l u r r i e s ....................................... 11 2 3 3 P o l y m e r S l u r r i e s ...................................... 13 2. 3. 4 P rop ert ies an d M eas ure m en ts . . . . . . . . . . . . . . 14 2 4 S p e c i f i c a t i o n E v o l u t i o n ......................................... 17 2. 5 W et H ole Co ns tru cti on an d S ha ft Ca pa cit y . . . . . . . . . . . . 22 2 6 C o n c r e t e P l a c e m e n t ........................................... 25 2 7 C o n c r e t e Q u a l i t y .............................................. 27 3 0 L a b o r a t o r y E q u i p m e n t a n d T e s t i n g ..................................... 40 3 1 C o n c r e t e P o u r S i m u l a t o r ........................................ 40 3 1 1 S h a f t ................................................ 41 3 1 2 S e a l i n g D e v i c e ........................................ 41 3 1 3 P u l l i n g D e v i c e ........................................ 42 3 1 4 S t o r a g e / M i x i n g S y s t e m ................................. 43 3 1 5 H o o t o n a n n y .......................................... 45 3 2 T e s t i n g M a t r i x ................................................ 45 3 2 1 V e l o c i t y ............................................. 46 3 2 2 W a i t T i m e ........................................... 46 3 2 3 S l u r r y P r o p e r t i e s ...................................... 47 3 3 S a n d F a l l o u t T e s t i n g ........................................... 48 3 4 F a l l o u t T e s t i n g R e s u l t s ......................................... 49

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ii 3 4 1 1 % S a n d C o n t e n t ...................................... 49 3 4 2 2 % S a n d C o n t e n t ...................................... 49 3 4 3 4 % S a n d C o n t e n t ...................................... 50 3 4 4 8 % S a n d C o n t e n t ..................................... 51 3 5 S i e v e A n a l y s i s o f F a l l o u t S a n d ................................... 51 3 6 E f f e c t o f S a n d A c c u m u l a t i o n .................................... 52 4 0 F i e l d S h a f t T e s t i n g .................................................. 68 4 1 P r o c e d u r e ................................................... 68 4 2 F i e l d S i t e s ................................................... 70 4. 2. 1 P ort of Ta m pa (E sse x C em en t) . . . . . . . . . . . . . 70 4.2.2 Crosstown Expressway Reversi ble Lanes Bridge . . . . . . 71 4 2 3 A l a g o n C o n d o m i n i u m s ................................. 73 4 3 H e a d D i f f e r e n t i a l S u m m a r y ..................................... 74 5 0 C o n c l u s i o n s a n d R e c o m m e n d a t i o n s ..................................... 87 R e f e r e n c e s ............................................................ 91 A p p e n d i c e s ............................................................ 94 A p p e n d i x A : T a b u l a r L a b o r a t o r y D a t a ................................ 95 A 1 A c c u m u l a t i o n T e s t i n g D a t a ............................... 95 A 2 S i e v e A n a l y s i s D a t a ..................................... 96 A p p e n d i x B : C o l l e c t e d F i e l d D a t a .................................. 101 B. 1 P ort of Ta m pa (E sse x C em en t) . . . . . . . . . . . . . 101 B 2 C r o s s t o w n E x p r e s s w a y ................................. 102 B 3 A l a g o n C o n d o m i n i u m s ................................. 106

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iii Li st o f T ab les Table 2-1 Desir able Slurr y Propertie s (after Fleming and Sliwinski 1977) . . . . 18 Table 2-2 Slurr y Specifications after FPS (1975) . . . . . . . . . . . . . . . 19 Table 2-3 Slurr y Specifications after Hutchinson et al. (1975) . . . . . . . . . 19 Ta ble 2-4 Sl urr y S pe cif ica tio ns af ter Ho lde n (1 98 3) . . . . . . . . . . . . . 21 Table 2-5 FDOT Slurry Specificat ions (1987) . . . . . . . . . . . . . . . . 22 T a b l e 3 1 S l u r r y D o s i n g C a l i b r a t i o n ....................................... 47 Ta ble 3-2 Pr esc rib ed Ve loc iti es f or H an d W inc h . . . . . . . . . . . . . . . 49 T a b l e A 1 1 % S a n d C o n t e n t .............................................. 95 T a b l e A 2 I n i t i a l 2 % S a n d C o n t e n t ......................................... 95 T a b l e A 3 R e f i n e d 2 % S a n d C o n t e n t ....................................... 95 T a b l e A 4 4 % S a n d C o n t e n t .............................................. 96 T a b l e A 5 8 % S a n d C o n t e n t .............................................. 96 T a b l e A 6 2 % S a n d C o n t e n t N o W a i t T i m e ................................. 96 Ta bl e A -7 2% Sa nd Con te nt 1 Hou r Wa it Ti me . . . . . . . . . . . . . . . 96 Ta bl e A -8 2% Sa nd Con te nt 2 Hou r Wa it Ti me . . . . . . . . . . . . . . . 97 Ta bl e A -9 2% Sa nd Con te nt 4 Hou r Wa it Ti me . . . . . . . . . . . . . . . 97 Ta bl e A -1 0 2 % S an d Co nt en t, 12 Hou r Wa it Ti me . . . . . . . . . . . . . . 97 Ta bl e A -1 1 4 % S an d Co nt en t, No Wa it Ti me . . . . . . . . . . . . . . . . 98 Ta bl e A -1 2 4 % S an d Co nt en t, 1 Ho ur Wai t T ime . . . . . . . . . . . . . . 98

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iv Ta bl e A -1 3 4 % S an d Co nt en t, 2 Ho ur Wai t T ime . . . . . . . . . . . . . . 98 Ta bl e A -1 4 4 % S an d Co nt en t, 4 Ho ur Wai t T ime . . . . . . . . . . . . . . 99 Ta bl e A -1 5 4 % S an d Co nt en t, 12 Hou r Wa it Ti me . . . . . . . . . . . . . . 99 Ta bl e A -1 6 8 % S an d Co nt en t, No Wa it Ti me . . . . . . . . . . . . . . . . 99 Ta bl e A -1 7 8 % S an d Co nt en t, 1 Ho ur Wai t T ime . . . . . . . . . . . . . . 100 T a b l e B 1 P o r t o f T a m p a S h a f t D a t a ...................................... 101 Table B-2 Measur ed Head Differentials for the Port of Tampa . . . . . . . . . 101 Table B-3 Crosstown Express way Shaft Data (No. 156) . . . . . . . . . . . 102 Table B-4 Crosstown Express way Shaft Data (No. 18) . . . . . . . . . . . . 102 Table B-5 Crosstown Express way Shaft Data (No. 167) . . . . . . . . . . . 102 Table B-6 Measur ed Head Differentials for Crosst own Expressway ( S h a f t N o 1 5 6 )............................................... 103 Table B-7 Measur ed Head Differentials for Crosst own Expressway ( S h a f t N o 1 8 )................................................ 104 Table B-8 Measur ed Head Differentials for Crosst own Expressway ( S h a f t N o 1 6 7 )............................................... 105 T a b l e B 9 A l a g o n S h a f t D a t a ............................................ 106 Table B-10 Head Differential Dat a for Alagon Shaft . . . . . . . . . . . . . 106

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v Li st o f F igu res Figure 1-1 Singl e 6 Foot Diameter Shafts are Used to Support Each B r i d g e P i e r S h o w n ............................................. 1 Figure 1-2 Visi ble Shaft Anomalies Due to Poor Constructi on Methods . . . . . . 3 Figure 2-1 Schematic of Typical Dri lled Shaft (O’Neil l and Reese, 1999) . . . . . 30 Figure 2-2 Dry Constr uction Proces s (O’Neill a nd Reese, 1999) . . . . . . . . 30 Figure 2-3 Stat ic Wet Construction Proces s (CALTRAN S, 1997) . . . . . . . . 31 Figure 2-4 Slur ry De-sanding Proc ess (CALTRANS, 1997) . . . . . . . . . . 31 Fi gu re 2 -5 T rem ie P ipe an d H op pe r P lac em en t to Bo tto m of Bo reh ole . . . . . . 32 Figure 2-6 Casing Const ruction Me thod (O’Neill and Reese, 1999) . . . . . . . 32 F i g u r e 2 7 V i b r o h a m m e r a n d C a s i n g ...................................... 33 Fi gu re 2 -8 N atu ral Sl urr y (G rou nd wa ter ) in Bo reh ole . . . . . . . . . . . . . 33 F i g u r e 2 9 B e n t o n i t e P o w d e r ............................................. 34 Figure 2-10 Overal l Filtr ation Proces s (Majano e t al., 1994) . . . . . . . . . . 34 Figure 2-11 Fil trati on and Filter Cake Buildup ( F l e m i n g a n d S l i w i n s k i 1 9 7 7 ) .................................. 35 Figure 2-12 Bentoni te Bonding (Beresford et al., 1989) . . . . . . . . . . . . 35 F i g u r e 2 1 3 E x a m p l e s o f P o l y m e r S l u r r y .................................... 36 F i g u r e 2 1 4 M u d B a l a n c e K i t ............................................. 36 Figure 2-15 Mar sh Cone Funnel and Measur e Cup . . . . . . . . . . . . . . 37 Fi gu re 2 -16 AP I S an d C on ten t T est Co m po ne nts . . . . . . . . . . . . . . 37

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vi Fi gu re 2 -17 Si de Sh ear Re sis tan ce V ers us Di sp lac em en t of Be nto nit e and Polymer Drilled Shafts (Brown, 2002) . . . . . . . . . . . . 38 Fi gu re 2 -18 Le ach ed Co nc ret e f rom Ex ces siv e T rem ie P ull . . . . . . . . . . 38 Fi gu re 2 -19 Ob ser ve d C on cre te B eh av ior Du rin g P lac em en t ( F l e m i n g a n d S l i w i n s k i 1 9 7 7 ) .................................. 39 Fi gu re 2 -20 CS D R ati o V ers us He ad Di ff ere nti al f or L PC an d F ull S c a l e P o u r s ( G a r b i n 2 0 0 3 ) ..................................... 39 Figure 3-1 Schematic Drawing of Concrete Pour Simulator . . . . . . . . . . 54 F i g u r e 3 2 C o n c r e t e P o u r S i m u l a t o r ........................................ 54 F i g u r e 3 3 I n t a k e P l u m b i n g .............................................. 55 F i g u r e 3 4 D r a i n a g e P l u m b i n g ............................................ 55 F i g u r e 3 5 S e a l i n g D e v i c e ( P l u g ) .......................................... 56 Fi gu re 3 -6 F irs t-g en era tio n P ull ing De vic e . . . . . . . . . . . . . . . . . 56 Fi gu re 3 -7 S eco nd -ge ne rat ion Pu lli ng De vic e . . . . . . . . . . . . . . . . 57 F i g u r e 3 8 S l u r r y T a n k .................................................. 57 Fi gu re 39 Ga so li ne -p owe re d S lu rr y P ump . . . . . . . . . . . . . . . . . 58 F i g u r e 3 1 0 F D O T D r i l l R i g P u m p ......................................... 58 F i g u r e 3 1 1 S l u r r y M i x i n g D e v i c e ......................................... 59 F i g u r e 3 1 2 M i x i n g S l u r r y w i t h D e v i c e ..................................... 59 Fi gu re 3 -13 Co nc ret e P um p T ruc k w ith Bo om Ex ten de d . . . . . . . . . . . 60 Fi gu re 3 -14 Tr em ie P ou r w ith Bu ck ete d C on cre te . . . . . . . . . . . . . . 60 Figure 3-15 Test Matrix Fl owchart for 1% Sand Content . . . . . . . . . . . 61 Fi gu re 3 -16 Ac cu m ula tio n f or 1 % S an d C on ten t T est s . . . . . . . . . . . . 61 Fi gu re 3 -17 Ac cu m ula tio n f or I nit ial 2% S an d C on ten t T est s . . . . . . . . . . 62

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vii Fi gu re 3 -18 Ac cu m ula tio n f or R ef ine d 2 % S an d C on ten t T est s . . . . . . . . . 62 Fi gu re 3 -19 Ac cu m ula tio n f or 4 % S an d C on ten t T est s . . . . . . . . . . . . 63 Fi gu re 3 -20 Ac cu m ula tio n f or 8 % S an d C on ten t T est s . . . . . . . . . . . . 63 Fi gu re 3 -21 Su m m ary of Ac cu m ula tio n f or A ll S an d C on ten ts . . . . . . . . . 64 Figure 3-22 Sieve Analysis for 4% Sand Content Accumulation a n d P i t S a n d ................................................ 64 Figure 3-23 Weight Retained Vers us Sieve Opening for 4% Sand Content . . . . 65 Fi gu re 324 Sa nd Fa ll ou t a s P er ce nt ag e o f To ta l S an d i n Co lu mn . . . . . . . . 65 Fi gu re 3 -25 To tal Vo lum e o f S an d f or V ari ou s D iam ete r D ril led Sh af ts a t 4 % S a n d C o n t e n t ........................................... 66 Fi gu re 3 -26 Vo lum e o f F all ou t f or V ari ou s D iam ete r D ril led Sh af ts a t 4 % S a n d C o n t e n t ........................................... 66 Fi gu re 3 -27 De pth of Fa llo ut V ers us De pth of Dr ill ed Sh af t f o r 4 % S a n d C o n t e n t .......................................... 67 Figure 4-1 Weighted Tape for Differential M easurement . . . . . . . . . . . 76 F i g u r e 4 2 P l u m b b o b C o u n t e r w e i g h t ...................................... 76 Fi gu re 4 -3 R ese arc he rs T ak ing He ad Di ff ere nti al M eas ure m en ts . . . . . . . . 77 Fi gu re 4 -4 M ap of He ad Di ff ere nti al M eas ure m en t S ite s . . . . . . . . . . . 77 Figure 4-5 Dril led Shaft Constructi on at the Port of Tam pa . . . . . . . . . . 78 Figure 4-6 Cage Ins tallat ion at Port of Tampa (Large Clear Spaci ng) . . . . . . . 78 Fi gu re 4 -7 V iew of Sh af t be fo re P ou r at Po rt o f T am pa ( G W T a t 6 F e e t B e l o w G r a d e ) ................................... 79 Fi gu re 4 -8 C SD Ra tio Ve rsu s H ead Di ff ere nti al f or P ort of Ta m pa . . . . . . . 79 Figure 4-9 Upward Veloci ty Versus Head Differential for Port of Tam pa . . . . . 80 Fi gu re 4 -10 Dr ill ed Sh af t C on str uc tio n a t th e C ros sto wn Ex pre ssw ay . . . . . . 80

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vii i Figure 4-11 Cage Ins tallat ion at the Cros stown Expressway ( S m a l l C l e a r S p a c i n g ) ......................................... 81 Fi gu re 4 -12 He ad Di ff ere nti al M eas ure m en ts a t C ros sto wn Ex pre ssw ay . . . . . 81 Figure 4-13 Visi ble Concrete I nside the Reinforce ment Cage During End of Pour at Crosstown Expressway ( M o n o p i e r C a g e C o n s t r u c t i o n ) ................................. 82 Figure 4-14 CSD Ratio Versus Head Differenti al for Crosstown E x p r e s s w a y ................................................. 82 Fi gu re 4 -15 Up wa rd V elo cit y V ers us He ad Di ff ere nti al f or C r o s s t o w n E x p r e s s w a y ........................................ 83 Fi gu re 416 Dr il le d S ha ft Con st ru ct io n a t A la go n Co nd omi ni ums . . . . . . . . 83 Fi gu re 417 Buc ke t P ou r a t A la go n Co nd omi ni ums . . . . . . . . . . . . . . 84 Figure 4-18 Resear cher Taking Concret e Depth Measure ments at Alagon . . . . . 84 Figure 4-19 Upward Veloci ty Versus Head Differential for an Alagon S h a f t ...................................................... 85 Fi gu re 4 -20 Su m m ary of CS D R ati o V ers us He ad Di ff ere nti al f o r A l l S i t e s a n d L a b D a t a ..................................... 85 Fi gu re 4 -21 Su m m ary of Ve loc ity Ve rsu s H ead Di ff ere nti al D ata f o r A l l S i t e s ................................................. 86 Figure 4-22 Recomm ended CSD Range for Drilled Shaft Constructi on . . . . . . 86 Figure 5-1 Behavior of Rising Concrete in Tre mie Poured Drilled Shaft . . . . . 90

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ix Slurry Sand Content and Concrete Interacti on in Drilled Shaft Construct ion Gr eg ory Ge ne De ese ABSTR ACT Due to the widespre ad use of drille d shafts in stat e and federal highway br idges, str ict reg ula tio n o f t he de sig n a nd co ns tru cti on ha ve be en im po sed by the res pe cti ve ag en cie s. Ho we ve r, d oc um en ted cas es o f a no m ali es a nd /or po orl y p erf orm ing sh af ts co nti nu e to ari se. To thi s en d, thi s th esi s in ve sti ga tes sev era l as pe cts of dri lle d s ha ft construct ion that may affect the qualit y of the finished product. Thes e areas i nclude be nto nit e sl urr y p rop ert ies an d p erf orm an ce a s w ell as r ein fo rce m en t ca ge an d c on cre te flow interacti ons. Recent resea rch indica tes tre mie poured concrete does not flow as predicted. Instead of even ri sing, a differentia l between the he ight of concrete inside and out side the rei nf orc em en t ca ge ha s b een ob ser ve d. Co m po un din g th is p rob lem is t he fa ct t ha t bentonite s lurry used t o support borehol es may settle suspended s and at the t oe of the shaft or on the sur face of rising concre te during l ong wait periods affording the po ssi bil ity of so il i nc lus ion s in the sh af t. T his the sis ex am ine s tw o m eth od s o f i nq uir y to quantify the behavi or of concrete i n a tremie pour dril led shaft and sand sus pension behavior of bentonit e slurry. Concl usions and rec omm endations ar e made to im prove pertinent construct ion regulat ions to ensur e quality of dri lled shafts.

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1 1.0 Introduction Drilled sha fts have become a com mon type of deep f oundation in t he State of Fl ori da e sp eci all y in ge olo gic al f orm ati on s n ot c on du civ e to pil e d riv ing or w he re en orm ou s la ter al s tif fn ess is r eq uir ed T he se c yli nd ric al c on cre te f ou nd ati on s ar e excavated usi ng an auger to a s pecified depth, where competent bearing str atum exists. The shaft size can t ypically r ange anywhere from 2 to 10 feet in diameter and can be up to 3 00 fe et d eep In m an y c ase s, the tre m en do us ax ial an d la ter al c ap aci ty m ak e si ng le sh af t f ou nd ati on s a v alu ab le a ttr ibu te i n c on ge ste d u rba n a rea s. Fi gu re 1 -1 s ho ws a ca se wh ere a si ng le 6 fo ot d iam ete r sh af t w as u sed to s up po rt e ach bri dg e p ier T his str uc tur e was construct ed with limited right -of-way between two exist ing bridges. Figure 1-1 Singl e 6 Foot Diameter Shafts are Used to Support Each Bridge Pier Shown

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2 In g en era l, t he co ns tru cti on of a d ril led sh af t re qu ire s th ree ba sic ste ps : (1 ) excavate ( drill) a hole, (2) pl ace reinforce ment steel, and (3) pour concrete i nto the hole. Ea ch ste p, ho we ve r, i ntr od uc es a ho st o f l og ist ica l is su es t ha t m us t be ad dre sse d in ord er to p rod uc e a r eli ab le s tru ctu ral ele m en t. A sid e f rom the req uir em en ts a sso cia ted wi th drilli ng a large di ameter hole, there e xist numerous problems when trying to maintain the excavation wal l stabil ity. Methods of m aintaini ng this sta bility va ry, but no one method provides both e conomy and assured quality. Reinforci ng cage configurati on and pla cem en t ha ve the ir o wn set of co m ple xit ies ste m m ing fr om de sig n re qu ire m en ts, lifting, and cent ering the c age in the exc avation. For i nstance, longe r shafts (over 100 feet deep) often requi re the cage to be placed i n sections whic h necessit ates some form of connection t o be made while lifted over the e xcavation. Fina lly, the conc rete mix design and the concre ting proces s have yet anot her set of obstac les that must be overcome. Therein, both t he fresh and cured pr opert ies of the concre te must m eet pouring a nd strength r equirements, respect ively. Furthe r, the concr ete place ment m ethod cannot degrade eit her of these proper ties. Du e to the wi de sp rea d u se o f d ril led sh af ts i n s tat e an d f ed era l hi gh wa y b rid ge s, strict regulati on of the design and const ruction have been imposed by the respect ive ag en cie s. Ho we ve r, d oc um en ted cas es o f a no m ali es a nd /or po orl y p erf orm ing sh af ts co nt in ue to ar is e. Fi gu re 12 s ho ws so il in cl us io ns in li ne of d ri ll ed sh aft s u se d t o fo rm a secant pil e wall. As most shafts are never une arthed, such a nomalies can go undetecte d. In this ca se, soil debr is left at t he bottom of the excavation was deposi ted throughout the length of the shaft. To thi s end, this t hesis inves tigates several a spects of dril led shaft

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3 construct ion that may affect the qualit y of the finished product. Thes e areas i nclude be nto nit e sl urr y p rop ert ies an d p erf orm an ce a s w ell as r ein fo rce m en t ca ge an d c on cre te fl ow int era cti on s. Th e o rga niz ati on of the the sis de scr ibe s tw o m ain m eth od s o f i nq uir y a s th ey relate to the anomaly formation in drilled s hafts. Chapter 2 revi ews the dril led shaft construct ion methods as well as appli cable slur ry propert ies. Important factors and characte risti cs pertai ning to slur ry material are discussed, as well as slur ry mixing m eth od s. Pr ev iou s re sea rch pe rta ini ng to s an d c on ten t in be nto nit e sl urr y m ixe s ar e al so summ arized. Figure 1-2 Visi ble Shaft Anomalies Due to Poor Constructi on Methods

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4 Chapter 3 discus ses the la boratory equi pment and testing. The constr uction of a concrete pour simulator is disc ussed. The test ing matrix and revisi ons/refinements to the data coll ection proc ess are al so elaborat ed. Results and cor relati ons are made pertaini ng to s an d s ett lem en t as a f un cti on of po ur v elo cit y, wa it t im e, an d s lur ry p rop ert ies Ch ap ter 4 d esc rib es t he fi eld tes tin g p rog ram It vis its in de tai l, e ach ob ser ve d co ns tru cti on sit e an d in clu de s in fo rm ati on on the ins tal led dri lle d s ha ft s. Al so dis cu sse d are the common construction methods as relat ed to regula tory speci fications. Final ly, the collect ed head differential data is di scussed and anal yzed with respe ct to concr ete mix, clear spa ce to diameter rat io (CSD), and pour veloci ty. Ch ap ter 5 p res en ts a su m m ary an d c on clu sio ns R eco m m en da tio ns an d f ina l co nc lus ion s ar e d isc us sed pe rta ini ng to t he ef fe cts of slu rry san d c on ten t an d w et concrete he ad differential. Changes to specificat ions are pr oposed to str engthen the co ns tru cti on qu ali ty o f d ril led sh af ts u nd er s lur ry. A s co pe fo r f utu re r ese arc h is als o presented.

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5 2. 0 L ite ra tu re R ev iew A t ho rou gh lit era tur e re vie w w as c on du cte d to ini tia te a nd fo cu s th e sc op e o f t his thesis. The t opics of this li teratur e review incl ude a histor y of drilled shafts, Fl orida De pa rtm en t of Tr an sp ort ati on (F DO T) ap pro ve d d ril led sh af t co ns tru cti on m eth od s, slu rry typ es, slu rry pro pe rti es a s re lat ed to d ril led sh af t co ns tru cti on e vo lut ion of slu rry sp eci fi cat ion s, ef fe ct o f s lur ry o n s ha ft cap aci ty a nd oth er p rev iou s re sea rch rel ate d to thi s thesis. Also, t he phenomenon of dif ferential he ad rising i s resear ched. 2.1 Histori cal Background Th e u se o f d ril led sh af ts f ou nd ati on s ca n b e d ate d to the ear ly 2 0 cen tur y in the th cities of Chicago and Detroit. The r apid growth taki ng place in t hese citi es drove the height of buildings upward as the skysc raper er a began (O’Neill and Reese, 1999). As the se b uil din gs co nti nu ed to r ise s o d id t he ir l oa din g. Th is a dv an ced to t he po int wh ere sh all ow fo un da tio ns we re n o lo ng er c ap ab le d ue to t he po or s tre ng th o f s ha llo w s tra ta i n these cit ies. Deep foundations, suc h as drill ed shafts, were devel oped to trans fer the ever-inc reasing l oads to deeper strata or bedrock with a dequate str ength. Th e ea rli est dri lle d s ha ft s w ere co ns tru cte d b y h an d e xc av ati on T he tw o p op ula r m eth od s in the ear ly 2 0 cen tur y w ere the Ch ica go m eth od an d th e G ow m eth od (O ’N eil l th and Reese, 1999). The Chicago method consist ed of digging a hole equal to the depth of the stave boa rds used to shor e its wall s. These boards were held in plac e by use of compression rings. The Gow method utilized a si milar approach, the di fference being the

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6 us e o f a tel esc op ing wa ll l ine r in ste ad of the sta ve bo ard s (G arb in, 20 03 ). B oth of the se m eth od s w ere fi na nc ial ly c om pe tit ive wi th d riv en pil es f or h eav y lo ad s. Hand digging was eventual ly replac ed by machine augering. Mr. Hugh B. W ill iam s’ c rea tio n o f p ow ere d a ug ers a nd ev en tua lly tru ck m ou nte d p ow ere d a ug ers le d to l arg er a nd de ep er s ha ft co ns tru cti on A ft er W W II, the bu ild ing bo om pro m pte d co ns tru cti on of ev en big ge r an d d eep er s ha ft s. Se ve ral co ntr act ors be cam e sp eci ali zed in drille d shaft excavati ons, and more efficient tools were deve loped (ADSC, 2004). The co nc ep t of a b ell ed o r un de r-r eam ed d ril led sh af t w as i ntr od uc ed B ell ed dri lle d s ha ft s ha d e xp an de d b ase s d esi gn ed to i nc rea se l oa d-c arr yin g c ap aci ty w ith ou t w ast ing co nc ret e on a wholly enlar ged shaft (Figure 21). As designs at the time only incorpor ated the co ntr ibu tio n f rom en d b ear ing a lar ge r ti p w as t ho ug ht t o b e th e so lut ion to h igh er capacity r equirements. This design i s rarel y used today due to c omplexities in the co ns tru cti on an d q ua lit y a ssu ran ce. The advances of construc tion dril ling technol ogy greatly out paced the the ories of engineeri ng design and anal ysis. This la ck of inform ation led t o over-desi gned, co ns erv ati ve dri lle d s ha ft s th at w ere no t as co stef fe cti ve as d riv en pil es. Ho we ve r, extensive r esearch i n the 1960s and 70s was conduct ed to improve design and co ns tru cti on m eth od s (O ’N eil l an d R ees e, 19 99 ). T his res ear ch led to a gre ate r un de rst an din g o f h ow dri lle d s ha ft s tr an sf er l oa d, an d h en ce, m ore ef fi cie nt d esi gn s to uti liz e th e f ull po ten tia l. T he rei n, sid e sh ear wa s f ou nd to b e a d om ina nt c on tri bu tor to the ov era ll c ap aci ty, wh ile en d b ear ing cap aci ty w as f ou nd to s eld om fu lly de ve lop T he

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7 ne w f ou nd co st e ff ect ive ne ss o f t he se d esi gn pro ced ure s f or d ril led sh af ts g rea tly inc rea sed the ir a pp eal fo r de ep fo un dati on ele m en ts. 2.2 Drilled Shaft Construct ion Methods The FDOT currently approves several methods of drill ed shaft construc tion. The construct ion method nam e refers to t he type of excavati on support used i n the borehole The methods are: dry, wet (sl urry-dis placement), and temporary or permanent casi ng. Ea ch m eth od is e ff ect ive fo r di ff ere nt s oil co nd iti on s, an d a co m bin ati on of m eth od s m ay be used when appropri ate. A descri pti on of each method and appropriate use conditions follow. 2.2.1 Dry Construction Method The dry method is suitable for drilli ng in stable soil loca ted above the groundwater ta ble (GWT). Exam ples of stable materia ls include homogenous, stiff clay, or s an ds co nta ini ng so m e co he siv e m ate ria l. I t m ay als o b e u til ize d in so ils loc ate d be low the GW T p rov ide d th e so ils ha ve low pe rm eab ili ty a nd co nc ret ing op era tio ns can be completed quickly. For dry constr uction, a bore hole is dri lled to full de pth without provi ding any sidewall suppor t (Figure 22). Under-rea ming (belling) of the shaft follows dri lling co m ple tio n, if de sir ed A cle an ou t bu ck et i s u sed fo r f ina l cl ean ing of acc um ula ted wa ter or s po ils at t he bo tto m of the bo reh ole be fo re c on cre tin g c om m en ces G en era l dr y construct ion allows for concr ete to be pl aced via a t remie pipe or free fall. The FDOT regulates sever al parameters of dry method construct ion, and co nd iti on s u nd er w hic h it is a cce pta ble S tip ula ted is a lim ite d a m ou nt o f s eep ag e w ate r,

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8 les s th an 12 inc he s m ay acc um ula te i n b ore ho le o ve r a 4 ho ur t im e p eri od a ft er d ril lin g is completed and the borehole maintain stabili ty without adver se caving or s loughing (FDOT, 2000). Rarely is the dr y method applicable in Flor ida, however, when it i s used, a contingency pl an should be rea dy if subsurface conditi ons change. 2.2.2 Wet (Slurry Displ acement) Constr uction Method Th e w et c on str uc tio n m eth od th e f oc us of thi s th esi s, is a pp rop ria te f or s ite s where the GWT or soil conditions do not allow for a stabl e, dry excavat ion to be co m ple ted T he ba sis fo r st ab ili ty i n th is m eth od lie s in m ain tai nin g a hig h f lui d p res su re inside the borehole re lative t o subsurface piezometric c onditions. To acc omplish this, a drilli ng slurry i s used to fill t he borehole t o a level hi gher than the local GWT, typically a dif fe ren tia l of 6 to 8 f eet (A DS C, 20 04 ). T his pro m ote s an ou tw ard hy dro sta tic pre ssu re which substanti ally disc ourages cavi ng. Se ve ral dif fe ren t dr ill ing slu rri es a re a va ila ble an d a re a pp rop ria te f or v ary ing sit e conditions. The ge neral cat egories ar e natural mineral, or polymer. Characteri stics and uses of each categor y will be ela borated in Sec tion 2.3. Two processes can be ut ilized for sl urry contr ol or maintenance: ( 1) stati c, or (2) reverse c irculat ion. In the st atic proc ess (Figure 2-3), most comm on in the U.S., drill ing co m m en ces us ing the dry m eth od un til the GW T i s en co un ter ed a t w hic h p oin t pr op erl y m ixe d s lur ry i s in tro du ced int o th e b ore ho le. Th is s lur ry i s m ain tai ne d a t a h igh er l ev el than the pie zometric surface at al l times during the r emainder of the drilli ng. The m ini m um rec om m en de d le ve l of dif fe ren tia l is 4 f eet (F DO T, 20 00 ). T he rev ers e circula tion proces s is an alt ernate choi ce. This method consists of cir culating s lurry and

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9 cuttings upwar d through the hol low stem of the auger tool by means of a pum p. The slurry i s circul ated through a series of scr eens which remove spoils from the mixture and reintr oduces clean, c onditioned sl urry back int o the borehole (Figure 2-4) Concrete plac ement is via tremie pipe (Figur e 2-5) in t his method and will be discussed i n Section 2.6. It is necessa ry to charge the tremie by seali ng the bottom and fi lli ng the pip e w ith co nc ret e w hil e it is r est ing at t he fl oo r of the ho le. A c ran e th en lif ts the tre m ie s lig htl y, wh ich bre ak s th e se al a nd su rge s th e co nc ret e o ut o f t he tre m ie. Th is he lps the co nc ret e “g et u nd er” the slu rry an d b eg in t o d isp lac e it ou t of the bo reh ole (O’Neill and Rees e, 1999). The tremie pipe is required t o stay 5 feet below the top surface of rising conc rete thr oughout the pour. 2.2.3 Casing Construction Method The casing method is intende d for use on sites wher e excessive caving may not be res ist ed by dri lli ng slu rry alo ne It is a lso us ef ul f or s oil /ro ck fo rm ati on s th at m ain tai n stabili ty until dr illed, or to seal off the borehol e from the GW T. The casing consis ts of a tem po rar y b ore ho le l ine r w hic h is typ ica lly m ad e f rom ste el p ipe T he cas ed m eth od can be used in conjunc tion with both wet and dry constr uction tec hniques. In c asi ng co ns tru cti on th e sh af t is dri lle d th rou gh un sta ble str ata us ing the we t method until an impervious layer i s reached. I n an effort to seal i n the nearl y impervious lay er, a ca sin g is ins ert ed int o th at f orm ati on D ry m eth od dri lli ng is t he n u til ize d u nti l de sir ed de pth is r eac he d. An alt ern ate m eth od is t o u se a vib roha m m er t o in ser t a f ull length casi ng, and drill to depth after i nsertion i s complete (Figure 2-6 a nd 2-7). Co nc ret e p lac em en t is by tre m ie, sim ila r to the we t m eth od A ft er c on cre tin g is

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10 completed, the temporary casing i s removed. Care m ust be taken t o ensure the l evel of co nc ret e is hig h e no ug h to dis pla ce t rap pe d s lur ry o r w ate r ou tsi de the cas ing up wa rds instead of mixing with fresh concret e. Also, some research (Mul lins et a l., 2004) ind ica tes tha t sl um p lo ss o f w et c on cre te i n c ase d c on str uc tio n m ay ha ve an ad ve rse effect on skin friction c apacity. 2. 3 D ril lin g S lu rry Drilling s lurrie s (fluids) have been extensi vely developed a nd used by the petroleum drilli ng industry. Before the 1960s, it was comm on practic e for the foundation contract or to util ize on-si te clay material s for use as dril led shaft slur ry. Due to the dif fi cu lty of co ntr oll ing the pro pe rti es o f t he se m ak e-s hif t sl urr ies th ey we re w ide ly replaced by be ntonitebased fluids that were easier to control and exhibite d better s and suspension prope rties. There are se veral type s of slurr ies in use for dr illed sha ft excavation t oday. The three most comm on types are: natural, mineral a nd polymer. A description of each type fo llo ws : 2. 3. 1 N atu ra l S lu rri es Natural sl urries e ssential ly consist of fresh or salt water either pl aced in the s haft or n atu ral ly o ccu rri ng as g rou nd wa ter (F igu re 2 -8) W ate r it sel f i s so m eti m es a n excellent drilli ng fluid. Its uses include suppor t of form ations tha t are per meable but do no t sl ou gh wh en gro un dw ate r pr ess ure s ar e b ala nc ed an d th e si de wa lls are no t er od ed (O ’N eil l an d R ees e, 19 99 ). I t is cri tic al w he n u sin g a na tur al s lur ry t o m ain tai n a he ad differential above the piezometric sur face to ensure no i nflow will comprom ise stabi lity.

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11 This is espec ially i mportant since the spe cific gravit y of natural slur ry (i.e. wate r) insi de and outside t he borehole ar e equivalent unlike bentoni te slurr y which is sli ghtly denser 2. 3. 2 M in era l S lu rri es Th e m os t co m m on m ate ria l us ed fo r m ak ing slu rry b en ton ite w as p ate nte d a s a ge lli ng an d s us pe nd ing ag en t f or s oil cu tti ng s in 19 29 (19 99 ). A tta pu lgi te a nd sep iol ite als o m ine ral s cl ass if ied un de r th e sa m e ca teg ory b eh av e q uit e d if fe ren tly rel ati ve to be nto nit e. As a re su lt, the y a re u sed fo r di ff eri ng dri lli ng en vir on m en ts a s d isc us sed below. Bentonite. This name refers to a specific mineral de posit found in the st ate of Wyom ing. Bentonite is a clay powder (Fi gure 2-9) which c onsists of sodium m ontmorillonite and exhibits t he abilit y to swell by absor bing large qua ntitie s of water (Fleming, 1977). W hen mixed with water, these cl ay materials form a colloidal sus pension (O’Neil l and Re ese 1 99 9). Th e b en ton ite po wd er d isp ers es i nto m icr os co pic pla telik e p art icl es which repel ea ch other when bound by water (similar to touc hing the same poles of two m ag ne ts) a llo wi ng the be nto nit e to co un ter act set tli ng an d re m ain in s us pe ns ion alm os t ind ef ini tel y. Th e p roc ess req uir ed fo r th is, hy dra tio n, us ua lly tak es a pe rio d o f s ev era l ho urs to c om ple te. Af ter wa rds th e sl urr y is rea dy fo r f ina l m ixi ng an d in tro du cti on int o the borehole In t he bo reh ole th e u se o f b en ton ite slu rry is f or s tab ili ty. Bo reh ole (si de wa ll) stabili ty is a re sult of a net outflow of slurr y to the surr ounding soil formations maintained by keeping slur ry head higher than the GWT. The outflow action of bentonite ha s been termed filtrat ion (O’Neill and Reese, 1999). Filt ration i s the acti on of

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12 bentonite mineral pl ates deposi ting on the wall s of the borehole ( Figure 2-10 and 211). Th is d ep os it t ha t co nti nu es t o b uil d u p is cal led a f ilt er c ak e. On ce a su bs tan tia l f ilt er cake forms, filtration ceas es and stabi lity is afforded by lateral pressure. Thi s effective str ess is t he dif fe ren ce b etw een the hig he r f lui d p res su re i ns ide the bo reh ole an d th e p ore pressures in the surr ounding soil. This action, however, i s contingent on the abili ty of the filter cake to seal voi ds. For soil wit h no large voids bentonite wil l seal qui ckly. For coarser s oil grai ns (i.e. gra vel) which may have larger voids, seali ng action is dependent on differential hydr ostatic pressure, t he grain-s ize dist ribution of the gr avel, and the slurry she ar stre ngth (Nash, 1974). An oth er u sef ul c ha rac ter ist ic o f b en ton ite is i ts a bil ity to s us pe nd cu tti ng s in solution for ci rculati on drilli ng. This stems from its thi xotropic, or gelling, pr operties Th e p lat e-l ike be nto nit e p art icl es a re n eg ati ve ly c ha rge d o n th e su rf ace a nd po sit ive ly charged on the e dges. Through three dimensional bonding, t he gel is formed by the att rac tio n o f t he ne ga tiv e su rf ace to t he po sit ive ed ge (F igu re 2 -12 ). T he se b on ds are we ak h ow ev er, an d c an be bro ke n b y a git ati ng the slu rry (R ees e, 19 85 ). L ab ora tor y tes tin g b y F lem ing an d S liw ins ki ( 19 77 ) an d R ees e (1 98 5), ind ica ted a cr iti cal be nto nit e co nc en tra tio n w ith reg ard to s ed im en t su sp en sio n. Ab ov e 4 % (b en ton ite we igh t di vid ed by water weight) sediment was held in suspensi on for several hour s in unagita ted slurr y. However, below 4%, sand set tled out of stagna nt slurr y much m ore rapidl y. Another desir able proper ty of bentonite sl urry is i ts abili ty to serve as a lubri cant fo r th e d ril lin g p roc ess It he lps red uc e w ear on dri lli ng eq uip m en t an d re du ces so il resist ance when used in conj unction with ca sing (O’Neill and Reese, 1999).

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13 At tap ulg ite an d S ep iol ite These are the other pri mary form s of m ineral s lurrie s. Unlike bentonite, t hese minerals are not hydrated by water therefore, the y have the advant age of be ing us ed im m ed iat ely af ter ini tia l m ixi ng T he y a re a lso us ef ul i n s ali ne en vir on m en ts, where bentonit e tends to floccul ate. However, these types of slurries do not stay in suspe nsion with the l ongevity of bentonite. Hence they do not suspend s oil part icles as effectively as bent onite eit her. To ensure effectivenes s, frequent mixing must be em ployed. With regard to filt ration, instead of forming a filter cake, t hese materials cr eate a soft cl ay layer on t he walls of the bo reh ole wh ich ap pe ars to b e n ot o nly an ef fe cti ve fi lte r, b ut a lso is s co ure d o ff wi th e ase by ris ing co nc ret e (O ’N eil l an d R ees e, 19 99 ). A s th is l ay er o f p art icl es h as a rel ati ve ly low shear str ength, it i s not desir able for this l ayer to re main during concreting. 2. 3. 3 P oly mer Sl ur rie s Po lym erba sed slu rri es ( Fi gu re 213 ) ar e ra pid ly b eco m ing a v iab le a lte rna tiv e to tradit ional mineral slur ries. However, the y are curr ently acce pted in only 12 of the 21 sta tes wi th d ril led sh af t sp eci fi cat ion s (M ull ins et a l., 20 04 ). P oly m ers can be div ide d into two genera l types: na tural ( semi-synthetic) and syntheti c. Na tur al. Na tur al p oly m er s lur rie s co ns ist of sta rch es, gu ar/ xa nth an gu m w ela n g um s, an d c ell ulo se. Th ese m ate ria ls a re c ap ab le o f m ain tai nin g s ho rt t erm sta bil ity in h igh ly acidic envi ronments (e.g. organic soi ls), a prope rty not shar ed by other dri lling sl urries. Na tur al p oly m ers m ay als o b e b len de d w ith be nto nit e to lim it f ilt rat ion rat e. Th ese na tur al p oly m ers are als o b iod eg rad ab le w he n u sed alo ne d ism iss ing the dis po sal iss ue s associat ed with bentonit e (O’Neill a nd Reese, 1999).

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14 Sy nth eti c. The synthetic variety of polymer slurr y consists of long, cha in-like hy dro car bo n m ole cu les m ixe d w ith po tab le w ate r. L ike be nto nit e, po lym er s lur rie s re ly on ele ctr ica l re pu lsi on to m ain tai n s us pe ns ion in t he m ixt ure P oly m er s lur rie s w ill pe ne tr at e i nt o p er mea bl e fo rma ti on s w he n s lu rr y h ea d i n t he bo re ho le ex ce ed s t he GWT (O ’N eil l an d R ees e, 19 99 ). S inc e th e p oly m er s tra nd s ar e m ore ha irlik e, as o pp os ed to pla te l ike th ey do no t bu ild up a f ilt er c ak e an d f ilt rat ion m us t be co nti nu ou s to en su re the sta bil ity of the bo reh ole T his co nti nu ou s f ilt rat ion act ion req uir es t ha t sp eci al c are be tak en to e ns ure the slu rry he ad is k ep t ab ov e th e G W T a t al l ti m es. Fo r po lym er slu rri es, thi s is esp eci all y c rit ica l, s inc e th e u nit we igh ts o f t he se s lur rie s ar e es sen tia lly eq ua l to wa ter an d c av ing wi ll o ccu r if the slu rry he ad fa lls be low the pie zo m etr ic s urf ace even for a short t ime. Practitioner s typical ly use 2-3 feet more differential when using polymer slurry inst ead of m ineral. Agglomeration is another behavior ass ociated wit h polymer slurries. The po lym er s tra nd s ca n a tta ch the m sel ve s to cla y a nd sil t cu tti ng s in the bo reh ole A s a res ult a gg lom era ted m ass es e ith er t en d to set tle ou t or fl oa t in the slu rry T he se s lur rie s als o d o n ot s us pe nd sed im en t f or a ny ap pre cia ble tim e (O ’N eil l an d R ees e, 19 99 ). T his allows for polymer slurry r euse with minimal cleaning but als o necessit ates a cl ean out of the bottom of the borehole to col lect set tled sedi ment. 2. 3. 4 P ro pe rti es a nd Mea su rem en ts Dr ill ing slu rry m us t f all wi thi n c ert ain pa ram ete rs t o b e an ef fe cti ve sta bil ize r an d/o r su sp en din g a ge nt. Se ve ral im po rta nt p rop ert ies an d h ow the y a re m eas ure d w ill be elaborat ed here. This di scussion will be focused on bentonite -based dri lling sl urries.

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15 Slu rry De ns ity The density (uni t weight) of slur ry is a function of the a mount of be nto nit e an d s ed im en t co nta m ina tio n in the m ix. Ty pic all y p rop ort ion ed slu rry ha s a sp eci fi c g rav ity of ap pro xim ate ly 1 .0 3 to 1. 05 af ter ini tia l m ixi ng (O ’N eil l an d R ees e, 19 99 ). T his rel ati ve ly h igh de ns ity can he lp p rev en t sl ou gh ing of the so il, bu t ca n a lso add difficulty in ci rculati on. If the density be comes too high (e.g. too much sediment contamination), ther e may be diff iculty di splacing t he slurry wit h concrete, a ffording the po ssi bil ity of slu rry inc lus ion s (R ees e et al. 1 98 5). A s lur ry d en sit y to o lo w, ho we ve r, i s indicati ve of a low bentonite conc entrati on and may not exhibit desir able sediment suspension char acteri stics for ci rculati on drilli ng. Sl urr y d en sit y is m eas ure d w ith a m ud ba lan ce ( Fi gu re 2 -14 ). A m ud ba lan ce i s a cal ibr ate d le ve r-a rm sca le t o w eig h a kn ow n v olu m e o f s lur ry. Th is d ev ice all ow s ea sy an d a ccu rat e m eas ure m en ts t o b e ta ke n. Ho we ve r, c au tio n s ho uld be ex erc ise d to ob tai n a re pre sen tat ive sam ple a s m ud de ns ity wi ll g en era lly inc rea se d eep er i n th e sl urr y co lum n d ue to s an d s ett lem en t an d th e f loo r of the bo reh ole wi ll g en era lly yie ld t he wo rst case densit y. Viscosity This parameter is det ermined by the concentra tion of bentonite and thoroughness of the sl urry mixing. Viscosity measures the thixotropi c properti es of the slu rry s im ila r to sh ear str en gth A s v isc os ity inc rea ses s o d oe s th e ab ili ty t o m ain tai n de tri tus in s us pe ns ion (R ees e et al. 1 98 5). Ho we ve r, i f v isc os ity is t oo hig h, the slu rry will be difficult t o pump due to poor flow characterist ics. Low viscosit ies have the advantage of being pumped easily, but t he slurry may not contai n an adequate amount of bentonite for des irable s ediment suspension chara cteris tics.

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16 Th e m os t co m m on de vic e u sed to m eas ure vis co sit y is the Mar sh co ne fu nn el (F igu re 2 -15 ). A lth ou gh the m os t in dir ect m eas ure m en t, i t is the eas ies t an d q uic ke st t o obtain. This makes it popula r during const ruction. To use, one places a finger at the sm all ori fi ce a t th e en d o f t he co ne a nd fi lls up the co ne to a sp eci fi ed m ark ta kin g c are to pour the sl urry through t he screen t o prevent pebbl es or other obstructi ng solids from entering t he bottom orifice. The slurr y is allowed t o flow out of the cone and into a gra du ate d c up a nd the tim e ta ke n f or t he slu rry to f ill on e q ua rt i s re co rde d. Th is t im e is called t he Marsh cone vi scosity, which i s comm only used in spec ifications ( e.g. FDOT, 20 04 ). Sa nd Co nte nt. Th is m eas ure m en t de ter m ine s th e am ou nt o f c on tam ina tio n th at h as en ter ed the m ix. If the san d c on ten t is ve ry h igh th e co rre sp on din g d en sit y a nd vis co sit y may increase and lead t o false conclusi ons that adequa te slurr y is being ci rculate d. Also, a high sand conte nt reading i s undesirabl e because the slurry may not be able t o suspend the entir e amount of sand (O’Neill and Reese, 1999). Sand se ttling a t the base of the shaft or on the re inforcement cage may cause inclusions when the concrete i s poured. A s tan da rd A m eri can Pe tro leu m Ins tit ute (A PI ) sa nd co nte nt t est is u sed in s lur ry construct ion (Figure 216). A small sample of representative s lurry is poured into a burette. I t is dil uted with water and after it i s agitat ed, poured onto a No. 200 sie ve. The contents on t he sieve ar e washed to ensure all fines (materia l smaller than No. 200) have been passed thr ough, and the remainder is ba ckwashed into the burette vi a a funnel. The sand will event ually set tle to t he bottom and the percenta ge of sand can be read on t he burette.

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17 pH The pH is a measure of the acidity or alkalini ty of the slurr y. Different minerals and so ils can inf lue nc e th e p H o f b en ton iti c sl urr y. Th e p H o f e ff ect ive slu rry is s lig htl y alk ali ne (8 t o 1 1), an d m eas ure s sh ou ld b e ta ke n to ke ep it w ith in t his ran ge S lur ry t ha t be co m es a cid ic ( a co m m on by -pr od uc t of dri lli ng thr ou gh org an ic l ay ers ) w ill fa il t o perform its necessary functi ons and become thin and watery. Test ing pH can be done with pH paper or a ca librat ed meter. 2.4 Specificat ion Evolution Se ve ral au tho rs h av e p rop os ed ide al s lur ry p rop ert ies fo r bo reh ole sta bil ity in dri lle d s ha ft co ns tru cti on T he se r eco m m en da tio ns we re f irs t de riv ed fr om oil we ll dri lli ng res ear ch f oll ow ed by ind ep en de nt s tud ies It is i m po ssi ble to c rea te a pe rf ect set of slu rry sp eci fi cat ion s to be us ed fo r al l jo bs s o s ev era l st ipu lat ion s m us t be co ns ide red before select ing governing sl urry proper ties. A balanc ed approach and an unde rstanding of the interac tions between t he subsurface formations and slurr y are requi red. Sl urr y p rop ert ies ha ve no t on ly b een tai lor ed fo r sp eci fi c si te c on dit ion s, bu t al so for each stage of foundation const ruction. A desi rable sl urry for excavat ing may not be ap pro pri ate fo r co nc ret ing T ab le 2 -1 d em on str ate s th e ar ray of slu rry pro pe rti es t ha t ar e best suit ed for different stages of the c onstructi on process. A wide range for the various parameters can be obser ved here. A high densi ty and moderate to high vis cosity may be necessary t o seal wall voi ds in the bore hole and afford stabil ity, however, thi s mix can be detrimental duri ng concreti ng (e.g. difficult for concr ete to dis place slur ry). A low de ns ity lo w v isc os ity m ix i s m os t de sir ab le t o e ns ure fr ee f low ing co nc ret e an d e asy displacement of bentonite. However, t his mix is not well suit ed for stabili zing the

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18 bo reh ole or s us pe nd ing san d, an d th e b ott om of the ex cav ati on m ay ne ed to b e cl ean ed out before concret ing to remove settle d sediment. Hi gh de ns ity h igh vis co sit y s lur ry s us pe nd s sa nd we ll, bu t m ay lea ve a th ick fi lte r ca ke (ef fe cts of wh ich wi ll b e d isc us sed lat er) L ow de ns ity lo w v isc os ity slu rry le av es a t hi nn er fi lt er ca ke bu t d oe s n ot su sp en d s an d we ll T he se ar e s ome considerat ions that must be addres sed when developing si te-speci fic slurry pr operties The first att empt at num erical slurry spe cifications was made by the Federation of Pi lin g S pe cia lis ts ( FP S) in 1 97 5. Ba sed on dia ph rag m wa ll s pe cif ica tio ns th ey cre ate d Table 2-1 Desir able Slurr y Propertie s (after Fleming and Sliwinski 1977)

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19 pa ram ete rs f or d en sit y, vis co sit y, sh ear str en gth a nd pH A lso inc lud ed in t his publicati on were clauses pertaini ng to design and cons tructi on of drilled shafts us ing bentonite. Thes e early par ameters did not addres s sand content Hutchinson et al (1975) als o re co m m en de d s lur ry p rop ert ies fr om dia ph rag m wa lls T ab les 2-2 an d 2 -3 summ arize bot h sets of slurr y specificati ons. Table 2-3 Slurr y Specifications after Hutchinson et al. (1975) Table 2-2 Slurr y Specifica tions after FPS (1975)

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20 The FPS specifications a bove are for fresh bentoni te supplie d to the borehol e. The only stipul ation provi ded for slurry at time of concreting is tha t the bott om of the bo reh ole be cle an M ore rec en t st ud ies su gg est ed tha t th e v isc os ity ran ge wa s to o b roa d (Stebbins, 1986) However, density and pH requi rements are large ly similar to cur rent standards. Hutc hinson defines many m ore parameters tha n FPS and m akes changes for steps in t he construct ion process. Thi s set of specificat ions are r oughly similar to FPS wi th t he ex cep tio n o f a llo wa ble san d c on ten ts o f 3 5% a nd ov er 8 0 p cf de ns ity fo r sl urr y at time of concreting. Th ese ini tia l f ind ing s w ere fo llo we d u p b y re sea rch tha t at tem pte d to pla ce m ore controls on t he slurry pr operties Holden (1983) is a nother ear ly example of specificati ons for slurry pr operties based on the par ticular drilli ng activit y in the construct ion process. Thi s resear ch came as a direct r esult of the ina dequacy of the original FPS specifications on a project i n Australia Ta ble 2-4 de scr ibe s sl urr y s pe cif ica tio ns pro po sed by Ho lde n. Re lat ive ly stringent boundaries were put on density a nd Marsh cone vi scosity, and a llowable sand co nte nt w as m uc h lo we r, 2 % du rin g d ril lin g a nd 10 % at tim e o f c on cre tin g, co m pa red to ear lie r sp eci fi cat ion s. Ad dit ion al m eas ure m en ts, su ch as m ini m um be nto nit e concentrat ion, additi onal shear s trength t ests, and filt er cake thi ckness were added. A minim um value for diff erentia l head o f slurry rel ative to GWT was also specified. Ho lde n s ug ge ste d, ev en tho ug h h e su pp lie s a d eta ile d s et o f p ara m ete rs, tha t specificati ons need to be modified depending on the spe cific site conditions, a nd the equipment being used for optimal construct ion.

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21 Ev en so in 19 84 th e F DO T a do pte d th e 1 97 5 F PS va lue s w ith ou t te sti ng the ir ap pli cab ili ty t o ty pic al F lor idi an sit e co nd iti on s (S teb bin s, 19 86 ). I n la te 1 98 5, on the I595 project ne ar Ft. Lauderdal e, slurry mixes were unabl e to meet the FDOT (FPS) req uir em en ts. Th is d em on str ate d th e u rge nt n eed to r ev ise the sp eci fi cat ion s to m eet typical c onstructi on conditions for Flor ida. Ta ble 2-4 Sl urr y S pe cif ica tio ns af ter Ho lde n (1 98 3)

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22 In 1 98 7, af ter fi eld res ear ch fr om the I-5 95 pro jec t, t he FD OT de vis ed its ow n s et of slu rry sp eci fi cat ion s, su m m ari zed in T ab le 2 -5, wh ich are m ore su ite d f or t he so il typ es f req ue ntl y e nc ou nte red in F lor ida T he se s pe cif ica tio ns are lim ite d to sim ple tes ts which can be run by cont ractors or inspect ors in the fiel d, but indicat ive of the qualit y of the slu rry be ing us ed T he sp eci fi cat ion s ar e f or s lur ry w hic h is su pp lie d to the sh af t as we ll a s sl urr y in the bo reh ole be fo re c on cre tin g. Th ese va lue s re m ain vir tua lly un ch an ge d in the cu rre nt F DO T S tan da rd S pe cif ica tio ns T he Fe de ral Hi gh wa y Ad m ini str ati on (F HW A) ad op ted a sl igh tly m od if ied ve rsi on of the se v alu es, as w ell as several s tate DOTs. 2. 5 W et H ole Co ns tru cti on an d S ha ft C ap ac ity Much resear ch has been conduct ed on drill ed shaft load capac ity with re gard to different variabl es in the wet c onstructi on process. Since the filtra tion proces s of bentonite s lurry le aves a soft filter cake on the si des of the borehole, que stions of side shear capac ity have been br ought to light It was assumed that ri sing concret e during the po ur w ou ld e ff ect ive ly s co ur t he sid ew all s an d e sta bli sh bo nd wi th t he so il f orm ati on s to exhibit ca pacity si milar in magnitude to that of a shaft const ructed by the dry method. Table 2-5 FDOT Slurry Specific ations (1987)

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23 However, the abili ty to scour i s dependent on the concrete s hear str ength rela tive to t he sh ear str en gth of the fi lte r ca ke If the fi lte r ca ke ha s a r ela tiv ely gre ate r sh ear str en gth it may not be com pletely s coured (Thasnani pan, 1998). The bentonite fil ter cake forms from the continuous outflow of slurry to the su rro un din g s oil to m ain tai n s tab ili ty. Th is f ilt er c ak e g row s th ick er d uri ng lon g w ait pe rio ds be tw een dri lli ng an d c on cre tin g u nti l it be co m es i m pe rm eab le. Pa ram ete rs af fe cti ng thi s ca ke thi ck ne ss i nc lud e sl urr y p rop ert ies w ait tim e, an d th e am ou nt o f h ead differential bet ween slurry and t he piezometric surface. The FHWA (1999) m aximum allowable t hickness of filter cake is 0.1 inc hes. However, early r esearch ( Nash, 1974) ind ica tes tha t up to 0 .2 inc he s o f f ilt er c ak e m ay acc um ula te i n 2 4 h ou rs i n a slu rry su pp ort ed ho le. Th is a m ou nt o f t hic kn ess m ay be de tri m en tal wi th r eg ard to a xia l cap aci ty o f t he sh af t. P res en tly F DO T s pe cif ies the ex cav ati on can no t be lef t op en wi th a bentonite slurry l onger than 24 hours without overreaming the sides. Ce rna k (1 97 6) t est ed thr ee b arr ett es [ sh af ts] in s an dy gra ve ls. Th e f irs t ba rre tte [shaft] was constructed in a dr y excavation a nd concreted i mm ediatel y. The second and third were c onstructe d under bentonit e slurry a nd had wait times (from com pletion of drilli ng to concret ing) of 8 and 97 hours, res pectivel y. W hen tested a nd compared to the dry m eth od ba rre tte [s ha ft ], the sec on d a nd thi rd e xh ibi ted a d ecr eas e in sid e sh ear capacity of 43% and 56% respecti vely. These res ults indi cate that a majority of the reduction oc curred in t he initi al 8 hours. Fleming and Sliwinski (1977) r eported on 49 shafts t o analyze the influence of be nto nit e o n c ap aci ty. Ba sed on loa d-d ef lec tio n c urv es, the y d ete rm ine d, fo r bo th

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24 cohesive and noncohesive soi ls, bentonit e does not adver sely affect shaft capaci ty. Ho we ve r, t he y re co m m en d a 24 ho ur t im e li m it f rom co m ple tio n o f d ril lin g to concreti ng, as longer wait periods may have an effect on axial ca pacity. O’Neill and Reese ( 1992) teste d slurry pr operties on two similar drill ed shafts. Th e fi rs t s ha ft ut il iz ed sl ur ry wi th a M ar sh co ne vi sc os it y o f 37 se co nd s a nd a w ai t t ime of 5 h ou rs b etw een dri lli ng an d c on cre tin g. Th e se co nd sh af t ha d a 49 sec on d M ars h cone viscosi ty and 7 hours of wait ti me between drilling and conc reting. Load t esting of these shafts i ndicated onl y minor differences. Hence, the authors concluded that the difference in viscos ity of slurry di d not affect the load t ransfer of the shafts. Thasnanipan (1998) reported on be ntonite vi scosity and c onstructi on time on sh af t ca pa cit y d eg rad ati on E lev en sh af ts w ere ins tal led un de r sl urr y, va ryi ng vis co sit y and total c onstructi on time. Slurry head was kept at a constant l evel, measuring 3.3 to 5 fe et f rom the top of tem po rar y c asi ng tha t ex ten de d to the bo tto m of a so ft cla y la ye r, ap pro xim ate ly 5 0 f eet be low su rf ace T he sh af t le ng ths va rie d b etw een 13 0 to 20 0 f eet an d c on cre te p lac em en t f or t his pro jec t w as b y tr em ie. Af ter sta tic all y lo ad tes tin g e ach pile, it was determined that vis cosity does not have any apparent trend with sha ft cap aci ty. Ho we ve r, c on str uc tio n ti m e g rea tly af fe cte d s ha ft cap aci ty. Ca pa cit y f ell be low est im ate d v alu es a t ar ou nd co ns tru cti on tim es a rou nd 40 ho urs Brown (2002) studied c apaciti es of drilled s hafts cast under bentonite a nd po lym er s lur rie s, as w ell as t em po rar y c ase d c on str uc tio n. Al l sh af ts h ad ide nti cal dia m ete r an d d ep ths a pp rox im ate ly 3 fe et a nd 36 fe et, res pe cti ve ly. W ait tim es b etw een dri lli ng co m ple tio n a nd co nc ret ing ran ge d b etw een 1 a nd 24 ho urs E ach sh af t us ed an

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25 identica l concret e mix and a tremie pour. Static loa d tests conduc ted on each shaft ind ica ted tha t th e b en ton ite slu rry cas t sh af ts h ad red uc ed cap aci ty r ela tiv e to the oth er co ns tru cti on m eth od s. Th e au tho r su gg est s th is i s a d ire ct r esu lt o f t he fo rm ed fi lte r ca ke wh ich he ind ica ted wa s ea sil y id en tif iab le o n th e ex hu m ed be nto nit e sh af ts. He als o noted that t he high hydrauli c conductivi ty of the surroundi ng soil may have caused a more rapid form ation of a thick fil ter cake. Fi gure 2-17 depic ts the si de shear tr ansfer of the be nto nit e an d p oly m er s ha ft s, it i s ap pa ren t th at u nit sid e sh ear fo r be nto nit e sh af ts i s considerabl y lower than any of polymer or dry method shafts. 2. 6 C on cre te P lac eme nt One of the crucial qua lity ass urance aspec ts of drille d shafts is concr ete place ment in t he bo reh ole F urt he rm ore w he n in co nju nc tio n w ith we t co ns tru cti on pro ces s sh af ts, concreti ng is even more criti cal due to t he filter ca ke buildup. Two accepte d ways of placing concr ete are by free fall or by tremie pipe. In the first method, concrete is poure d directl y from truck and “dr opped” into the sh af t. I t is on ly a pp lic ab le i n th e d ry m eth od a s an y f lui d in the bo reh ole wi ll s eg reg ate the co nc ret e. W he re a cce pte d, fr ee f all ing co nc ret e is us ua lly lim ite d to a sh ort dis tan ce du e to the po ssi bil ity of seg reg ati on in t he we t m ix. Si nc e se gre ga tio n is m ore lik ely to oc cu r w he n f all ing co nc ret e st rik es a n o bs tru cti on re inf orc em en t ca ge s ad d to thi s d an ge r (O ’N eil l an d R ees e, 19 99 ). W he n p lac ing wi th t his m eth od a sh ort ch ute is e m plo ye d to direct t he concrete to the cent er of the borehole and away from excavation walls or the reinforcement cage.

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26 Th e se co nd m eth od us es a tre m ie p ipe or p um p h os e th at p lac es c on cre te d ire ctl y at t he bo tto m of the bo reh ole A tre m ie p ipe is m ad e f rom ste el t ub ing u su all y a tta ch ed to a feed hopper at t he top. This proce dure is used for wet c onstructi on process shafts, or in d ry s ha ft s w he re f ree fa lli ng co nc ret e m ay cau se t he bo reh ole to c oll ap se. A t rem ie pipe is sea led at the bottom by a plate (can be a steel or plywood disc) to e nsure no gro un dw ate r or slu rry en ter s th e tr em ie p ipe du rin g in ser tio n in to t he bo reh ole It is placed insi de the borehol e such that t he bottom of the tremie pipe is flush with the floor of the excavation. On ce i n p lac e, the tre m ie p ipe is f ill ed wi th c on cre te i n a pro ces s k no wn as ch arg ing T he sea l is bro ke n b y th e w eig ht o f t he co nc ret e as the tre m ie i s li ft ed sli gh tly (ap pro xim ate ly 1 tre m ie d iam ete r) a nd fl ow is a llo we d to co m m en ce ( O’ Ne ill an d R ees e, 1999). This weight i s responsibl e for the init ial force with whic h the concret e exits t he tre m ie, en su rin g th e co nc ret e f orc es i ts w ay un de rne ath the gro un dw ate r or slu rry O nc e the lev el o f s ou nd co nc ret e h as r ise n a bo ve the bo tto m of the tre m ie, Its rel ati ve ly h igh er density is responsibl e for displacement of pre-exis ting groundwater or slurr y out of the shaft. This process ensures tha t detri mental m ixing of wet concret e and groundwater or slu rry do es n ot o ccu r. T he po ur c on tin ue s, pe nd ing the he ad of co nc ret e in the tre m ie pipe is gre ater tha n the head in t he borehole. When sound concrete r eaches the t op of excavation, t he pour is complete. The tremie pour process i s dependent on car eful construct ion. If the init ial li ft of the tremie pipe is too high, leac hing of the first amount of concrete can oc cur (Figure 218 ) an d h av e ad ve rse ef fe cts on the fi nis he d s ha ft qu ali ty. It i s al so im pe rat ive to

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27 maintain the tremie pipe some distance unde r the leve l of advancing concre te. If the tre m ie p ipe is r ais ed ab ov e th e co nc ret e, m ore lea ch ing can oc cu r du e to dir ect co nta ct be tw een fl ow ing co nc ret e an d s lur ry w hic h m ay res ult in d ef ect s. FH W A r eco m m en ds a minim um of 5 feet penetrat ion into the wet concrete 2. 7 C on cre te Q ua lit y Ef fe cti ve co nc ret e f or s lur ry s up po rte d d ril led sh af ts s ho uld ex hib it s ev era l important charact eristi cs. Foremost, it must be workable, if it is placed by tr emie and fl ow thr ou gh the rei nf orc em en t ca ge to t he co ve r ar ea. It m us t al so co nta in a de qu ate shear str ength to effectivel y remove the filter cake bui ldup on the borehol e walls. A further desir able chara cteris tic is a relati vely long set time, as the entir e shaft may take sev era l ho urs to c om ple tel y p ou r. The flow characteri stics of tre mie poured concrete have be en resear ched and the ass um ed be ha vio r of co nc ret e ri sin g e ve nly thr ou gh the bo reh ole an d s co uri ng the fi lte r cake off sidewalls does not always descri be the natur e of the pour. Fleming and Sliwinski (1977) briefly descr ibe a pour where, due to tight r einforcement spacing, tre m ied co nc ret e ro se u p in sid e th e re inf orc em en t ca ge an d o nly af ter a cr iti cal he ad differential was r eached, “fell” pa st the cage to the cover area (Figur e 2-19). Brown (2003) offers a general di scussion of this phe nomenon and a case study. He suggests two types of problems with regard to reba r cages with s mall clear spaci ng due to high amounts of steel. The first involves sedi ment settling out of slur ry onto the top of rising concr ete. If the concr ete does in fact slough off to the side, the sediment will as well This accumulation may decrease bond the be tween concret e and the bear ing

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28 fo rm ati on H e su gg est s th at e ve n w ith cle an slu rry c on cre te c an be im pe de d e no ug h to create voi ds outside t he cage and diminish side s hear capaci ty. In t he cas e st ud y h e d esc rib es, tw o s ha ft s w ere dri lle d. Th e f irs t ut ili zed sta nd ard Al ab am a D OT ap pro ve d c on cre te w hic h c on sis ted of #5 7 c rus he d a gg reg ate (3/ 4 in ch maxim um diam eter) a nd a slump of 8 inches. The m inimum clear spa cing of the reinforcement cage was 5 inches He stated the concrete was obs erved to flow around the tre m ie p ipe an d f all ou t, r ad ial ly, tow ard the an nu lar sp ace of the sh af t. T he co nc ret e w as seen to fall t hrough the cage t o the cover r egion at a di fferential height of about 1.5 feet. Th e se co nd sh af t, c on str uc ted ide nti cal ly, ex cep t f or t he red uc tio n o f t he 3/4 inc h aggregate t o 1/2 inch. There was much less falli ng out observed i n this shaft. USF recently conduct ed resear ch to examine the flow of concrete in a dr illed sha ft on a la b-s cal e le ve l (G arb in, 20 03 ). A de vic e, the La ter al P res su re C ell (L PC ), w as developed to st udy various par ameters of concrete flow. The LPC was of tubular shape an d c on str uc ted of Lu cit e. A c irc ula r w ire m esh of dif fe ren t cl ear sp aci ng s w as u sed to sim ula te a rei nf orc ing cag e in sid e th e la b-s cal ed dri lle d s ha ft C em en t m ort ar w as u sed to s im ula te c on cre te. Th e p rim ary ob jec tiv e o f t he LP C w as t o te st t he ef fe ct o f c on cre te slu m p o n th e la ter al p res su re o f t he fi nis he d s ha ft b ut i t w as d isc ov ere d in the se s m all tre m ie p ou rs t ha t th e le ve l of ris ing co nc ret e in sid e o f t he wi re m esh wa s h igh er t ha n ou tsi de the wi re m esh T his pro m pte d re sea rch ers to r un an oth er s eri es o f t est s to examine this phenomena m ore fully. Th is s eri es o f t est s in clu de d th ree dif fe ren t ca ge sp aci ng s. A c lea r sp aci ng to diameter ratio ( CSD) defined the relat ionship between mortar ( concrete) aggregates and

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29 reinforcement cage spaci ngs. This rati o served to nor malize the size of the r ebar spaci ng to the lar gest aggrega te in the c oncrete mix. It w as d isc ov ere d th at t he m ort ar i n th e L PC ne ve r ro se u nif orm ly a s it wa s ass um ed In ste ad it wo uld fl ow up in sid e th e re ba r ca ge u nti l a c rit ica l po int wa s reached, and fall through the cl ear spaci ng to the outsi de. It was noted t hat when the ca ge sp ac in g wa s s mal l ( i. e. sma ll er CSD ) t he di ffe re nt ia l b ec ame hi gh er in di ca ti ng so me co rre lat ion be tw een CS D a nd he ad dif fe ren tia l. F igu re 2 -20 de pic ts t he rel ati on sh ip found between CSD and head differential in t he mortar pours as well a s full scale t esting completed. Th is h ead dif fe ren tia l ph en om en a ca us es a fl ow in t he bo reh ole tha t is co m ple tel y dif fe ren t f rom tha t an tic ipa ted T his be ha vio r no t on ly b rin gs int o q ue sti on the ide a th at the ris ing co nc ret e sc ou rs o ff the fi lte r ca ke lef t by be nto nit e sl urr ies b ut a lso int rod uc es the possibi lity of inclus ions in the s haft due to concret e falling onto se ttled material in the borehole outs ide the cage during longer wait periods between readymix concrete trucks. This thesis investiga tes the effects of both the CSD ratio and selec ted slurr y properti es on the constr uction of drill ed shafts.

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30 Figure 2-1 Schematic of Typical Dri lled Shaft (O’Neill and Rees e, 1999) Fi gu re 2 -2 D ry C on str uc tio n P roc ess (O’Neill and Rees e, 1999)

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31 Figure 2-3 Stat ic Wet Construction Proces s (CALTRAN S, 1997) Figure 2-4 Slur ry De-s anding Process ( CALTRA NS, 1997)

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32 Figure 2-5 Tremie Pipe and Hopper Pla cement to Bottom of Bo reh ole Fi gu re 2 -6 C asi ng Co ns tru cti on Met ho d (O ’N eil l and Reese, 1999)

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33 Figure 2-7 Vibrohamm er and Casing Fi gu re 2 -8 N atu ral Sl urr y (G rou nd wa ter ) in Bo reh ole

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34 Fi gu re 2 -9 B en ton ite Po wd er Fi gu re 2 -10 Ov era ll F ilt rat ion Pr oc ess (Majano et al., 1994)

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35 Figure 2-11 Fil trati on and Filter Cake Buildup (Fleming and Sliwinski, 1977) Figure 2-12 Bentoni te Bonding (Beresford et al., 1989)

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36 Fi gu re 2 -13 Ex am ple s o f P oly m er S lur ry Fi gu re 2 -14 Mu d B ala nc e K it

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37 Figure 2-15 Mar sh Cone Funnel and Measur e Cup Fi gu re 2 -16 AP I S an d C on ten t T est Co m po ne nts

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38 Figure 2-17 Side Shea r Resistanc e Versus Displac ement of B entonite a nd Polymer Drilled Shafts (Brown, 2002) Fi gu re 2 -18 Le ach ed Co nc ret e f rom Ex ces siv e T rem ie P ull

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39 Fi gu re 2 -19 Ob ser ve d C on cre te Behavior During Plac ement (Fleming and Sliwinski, 1977) Fi gu re 2 -20 CS D R ati o V ers us He ad Di ff ere nti al f or L PC an d F ull Sc ale Po urs (Garbin, 2003)

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40 3.0 Laboratory Equipment and Testing In order t o test sand fall out in a dri lled shaft bore hole supporte d by slurry, a l abscale appar atus was concei ved and developed. Dubbed the “concrete pour simulator,” this devic e was designed to s imulate rising conc rete in t he shaft. The design had t o allow fo r va ria ble tim e an d v elo cit y, as w ait tim e an d v elo cit y o f r isi ng co nc ret e w ere hy po the siz ed va ria ble s af fe cti ng san d f all ou t of a sl urr y. Th e o rig ina l de sig n h ad downfalls, so subsequent r efinements and their effects will be elaborat ed. Though this part of the researc h was considered l ab-scale it was desir ed that the de vic e b e as lar ge as p os sib le. It w as c rit ica l th at i t ha ve the he igh t to ad eq ua tel y e m ula te drille d shafts, and also a di ameter that would not li mit the applicabil ity of the experi ment. 3.1 Concrete Pour Simulator This unique devic e was envisioned a s a 20 foot tall, a bove ground, circ ular shaft wi th t he ab ili ty t o h old slu rry by m ean s o f a sea lin g d ev ice an d th e ab ili ty t o ra ise thi s sea lin g d ev ice at d if fe ren t ve loc iti es t o s im ula te t he ris e o f c on cre te i n a co m m erc ial ly co ns tru cte d d ril led sh af t. A lso ne ces sar y w as a tan k to sto re t he slu rry wh ile it w as n ot i n use, a pump to fill the shaft, a drai n pipe for slurr y to escape t o the tank from the top of the shaft, and a mounting device wit h easy access ibilit y to the top and bot tom of the sh af t. E ach co m po ne nt w ill be ela bo rat ed in t his sec tio n. Fi gu re 3 -1 s ho ws a co nc ep tua l sketch of the appar atus.

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41 3. 1. 1 S ha ft To sim ula te t he sh af t, a 20 fo ot l on g s ect ion of 12 inc h d iam ete r P VC pip e w as used (Figure 32). This pipe was se cured to two 4x6 inc h angles by rac heting str aps sin ce i t w as t o b e el ev ate d o ff the gro un d in ord er t o p lac e th e st ora ge tan k u nd ern eat h the pipe and t o allow for the easy pl acement of the sealing devic e at the bot tom. The pipe ass em bly wa s th en m ou nte d o n th e si de of the fr am e o f t he US F/ FH W Aow ne d 4 MN sta tna m ic d ev ice via a st eel tub e se cti on we lde d to the an gle s. Th e st atn am ic d ev ice fr am e p rov ide d th e n ece ssa ry h eig ht t o s up po rt t he de vic e an d th e w eig ht c on tai ne rs pro vid ed a w ork ing pla tf orm at t he top of the sh af t. T he hy dra uli c le gs of the sta tna m ic de vic e al so pro vid ed a co nv en ien t m eth od of ad jus tin g le ve lne ss o f t he PV C p ipe The plumbing was installed at the top and bott om of the shaft by dril ling and ta pp in g i nt o t he si de of t he pi pe T he in ta ke pl umbi ng (F ig ur e 3 -3 ) c on si st ed of a ca mloc k a da pte r f or e asy co nn ect ivi ty a nd a v alv e so tha t th e p um p c ou ld b e d isc on ne cte d after filling t he shaft. This plumbing was placed approxi mately one foot from the bottom of the pip e so the fu lly ins ert ed sea lin g d ev ice wo uld no t bl oc k s lur ry f rom be ing pu m pe d into the sha ft. Approximately one foot from the top of the shaft, the drainage pl umbing was install ed (Figure 34). This consis ted of segments of 2 inch PVC pipe draining directl y back into the storage t ank for slurry r euse. This all owed for approximately 18 feet of simulated concrete r ise in a gi ven experimental run. 3. 1. 2 S ea lin g D ev ice Th e se ali ng de vic e w as a cru cia l pa rt o f t he ass em bly It wa s n ece ssa ry t o de ve lop a p lug tha t w ou ld b e re lat ive ly e asy to p ull up an d y et h av e th e ca pa bil ity to s eal

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42 the pipe such t hat no slurr y could leak out even with the nor mal im perfections of the inner surface of the PVC. It would al so need the robus tness to wit hstand the weight of slu rry fo r up to t we lve ho urs at a tim e d uri ng the ex ten de d le ng th t est s. The plug was built from 3/4 inch plywood discs turned down to a dia meter of 11 .5 inc he s sa nd wi ch ing 1/8 inc h th ick rub be r di scs of 12 .5 inc h d iam ete r. T he se d isc s were center drille d and a 3/4 inch di ameter threaded rod was us ed to bolt t hem together. To the top en d o f t his rod a sh ack le w as a da pte d s uc h th at t he plu g c ou ld b e p ull ed through the pi pe. When inserted, the rubber would engage the inne r walls of the PVC pipe, creat ing a seal by whic h no slurry coul d leak. Af ter so m e p rel im ina ry t est ing it wa s f ou nd tha t th ree rub be r di scs cre ate d a n adequate sea l and did not pr ovide excessi ve drag which would incr ease the di fficulty of pulling the plug upward. Between each r ubber disc, t hree wood discs were placed to add str en gth an d e ns ure the lev eln ess of the plu g a s it wa s b ein g p ull ed (F igu re 3 -5) A c on sis ten t w ay of co lle cti ng set tle d s an d w as a lso req uir ed T he ref ore a pla sti c lip was att ached to the t op of the plug, which allowed for the fallout to be ca ught and removed easily. It al so ensured tha t no settl ed sand would escape t hrough the drai nage tu be at th e e nd of t he pu ll T hi s mod if ic at io n a ro se fr om l ea ka ge th at wa s n ot ed fr om a da m ag ed sea l. T his cau sed slu rry to p ass thr ou gh s im ult an eo us ly r em ov ing sed im en ted material. 3. 1. 3 P ul lin g D ev ice This component was responsible for r aising the plug through the shaft at varyi ng rat es o f s pe ed an d a lso pro vid ing the rea cti on fo r th e w eig ht o f t he slu rry T he fi rst

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43 generati on device was const ructed from 2x2 inch tubular st eel sect ions and incl uded a pu lle y to cen ter the cab le a nd a h an d w inc h to co ntr ol t he ve loc ity (F igu re 3 -6) T his device was mounted to a crossmem ber of the stat namic device via stee l plates and thr ead ed rod It wa s q uic kly dis co ve red tha t th e f ram e co uld no t su sta in t he wi nc h lo ad without causi ng yielding. After determining the load t o cause yiel ding of the frame, a m ore robust s econd generati on device was const ructed from a W 4x13 section ( Figure 3-7). I t mounted in the sam e m an ne r to the sta tna m ic d ev ice a nd wa s co ns tru cte d w ith ad dit ion al g us set pla tes to ensure st abilit y. Like its pr edecessor, t his device i ncorporate d a pulley to c enter the 3/1 6 in ch ste el c ab le o ve r th e co lum n w hil e th e p lug wa s w inc he d to the top at a co ntr oll ed ve loc ity T he wi nc h w as c ali bra ted by tur ns pe r se co nd to c on tro l ve loc iti es similar to those found in dr illed sha ft constructi on conditions ( approximately 1 to 4 fpm). This calibr ation was found to be easy t o maintain with the assi stance of a stopwatc h. The wi nc h a ls o i nc or po ra te d a lo ck in g mec ha ni sm t o h ol d t he pl ug du ri ng th e w ai t t ime before pulling. 3. 1. 4 S tor ag e/M ixi ng Sy ste m W hen not in use, t he slurry was s tored dir ectly bel ow the pipe in a bl ack 200 gallon plas tic tank ( Figure 3-8). Thi s tank was covere d for protecti on from environmental elements (i.e. r ain). Before intr oduction int o the shaft, the sl urry in the tank was mixed and various tes ts were run t o ensure proper slurry pr operties A powerful m ixi ng de vic e w as r eq uir ed to r e-s us pe nd san d th at h ad set tle d d uri ng sto rag e.

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44 Th e fi rs t mi xi ng de vi ce wa s a sma ll ga so li ne en gi ne po we re d c en tr if ug al pu mp tha t w as a lso us ed to i ntr od uc e sl urr y in to t he sh af t (F igu re 3 -9) It pro vid ed ad eq ua te pre ssu re t o m ix t he m ine ral slu rry bu t th e v ein s w ere eas ily clo gg ed wh en lar ge siz ed sand parti cles were i ntroduced int o the slurr y. Therefore, this pump required freque nt cl ea ni ng an d, du e t o c lo gg in g, te nd ed no t t o p as s a ll th e s an d t hr ou gh to th e s ha ft P ump pe rf orm an ce w ors en ed wi th h igh er s an d c on ten ts a nd be cam e u nu sab le. In t his lig ht, it was decided to upgr ade the mixing device to a pump that was designed for slurry us e. The second mixing device used was a hel ical-t ype pump f rom a FDO T drill r ig (Figure 310). It prove d much less vulnerable t o larger s ized part icles and hi gh sand contents but did not provide adequate ta nk agitati on to mix the slurry uniformly at higher sand co nte nts H en ce, it w as a lso ve ry i ne ff ect ive at r e-s us pe nd ing the set tle d s an d b ack int o the slurr y mixture. It was, however, well s uited to pump slurry int o the shaft once sand was in suspension. An innovative mixing device was conc eived after t he frustrati ons of failure of the first two pumps at higher sand cont ents. This devi ce was designed onl y to mix, as the dri ll r ig p um p w as s uf fi cie nt t o p um p s lur ry t o th e co nc ret e p ou r si m ula tor T his de vic e co ns ist ed of a ho rse po we r el ect ric m oto r dr ivi ng a sh af t co nn ect ed to a fi ve bla de fa n placed deep i nto the slur ry tank (Figur e 3-11). The fan blades wer e effective in agit ating the slu rry an d it wa s v isu all y a pp are nt t ha t th is s ys tem wa s m uc h m ore ef fi cie nt i n su sp en din g th e se ttl ed san d d ue to t he vio len t m ixi ng act ion (F igu re 3 -12 ). T his sy ste m pro ve d to be an ex cel len t m ixi ng sy ste m an d a llo we d f or t he m os t co ns ist en t sl urr y properti es to be obtai ned.

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45 3.1.5 Hootonanny Instead of dril l auger mixing or a slur ry gun, an innovati ve device cal led a Ho oto na nn y w as u sed to i ntr od uc e p ow de red be nto nit e in to t he slu rry T his de vic e u ses high velocit y water to cr eate suct ion that dr aws dry bentonit e through a tube and into the top of the de vic e. In t his cas e, the su cti on is c rea ted by wa ter or r e-c irc ula ted slu rry a t an inlet pr essure of approximately 20 psi The pressure c auses a viol ent mixing of be nto nit e p art icl es w ith the wa ter T he pic k-u p tu be int rod uc es t he po wd ere d b en ton ite into the ce nter of the fluid flow through a Teflon i nsert tha t eliminates st icking of partial ly hydrated be ntonite t o the walls of the devi ce. After extended use there was no evidence of agglomeration of dry bentoni te in the s lurry ta nk. The advantage of this de vice is t hat it al lows for quick and easy mixing of be nto nit e m uc h m ore cle an ly t ha n w ith tra dit ion al m eth od s. Un de r hi gh er p res su res su cti on is s tro ng a llo wi ng fo r la rge r am ou nts of be nto nit e to be m ixe d q uic kly T he on ly dis ad va nta ge ass oc iat ed wi th t he de vic e is an inf req ue nt c log gin g in the tub e, wh ich is us ua lly ass oc iat ed wi th a blo ck ag e th at c an be cau sed by try ing to p ick up too m uc h bentonite a t once. The device is very eas y to clean up by r insing with pot able water, a nd can be store d in a small space when not in us e. 3. 2 T est in g M atr ix The apparent var iables t hat influence sa nd settle ment were taken into account wh en the co nc ret e p ou r si m ula tor wa s b uil t. T he tes tin g m atr ix w as t ail ore d to sim ula te the wide vari ety of conditions t hat can be encount ered in dri lled shaft const ruction.

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46 Its aim was to identi fy how changing each of the following conditi ons would affect sand suspension. 3. 2. 1 V elo cit y Up wa rd v elo cit y o f r isi ng co nc ret e w as a co nc ern fo r bo th t he fi eld an d la b asp ect s o f t his the sis S inc e a h ead dif fe ren tia l w as o bs erv ed it wa s d esi red to d isc ov er i f sand accumulation was a function of upward concr ete veloci ty and evaluat e the incl usion potential of falling concrete on accumulation caused by thi s upward velocit y. The upward velocit y is dicta ted by the flow rate of concrete int o the shaft which is de pendent on the m eth od of co ns tru cti on em plo ye d. A c on cre te p um p tr uc k (F igu re 3 -13 ) w ill pro vid e a s tea dy fl ow of co nc ret e u nti l th e su pp ly i s ex ha us ted (i. e. rea dy -m ix t ruc k is em pti ed ). C on cre te p lac ed by the bu ck et m eth od (F igu re 3 -14 ) te nd s to fl ow at a hig he r rate due t o gravity and he ad of concrete st ored in the buc ket, governed onl y by the operator c ontrolli ng the mouth (open area) at the bottom of the bucket. Although the flow rate is affected by pla cement m ethod, upward veloci ty is als o a function of the cro sssec tio na l ar ea o f t he bo reh ole G ive n th at v elo cit y is eq ua l to fl ow rat e(Q ) di vid ed by cro sssec tio na l ar ea( A) ri sin g c on cre te v elo cit ies fo r va rio us dia m ete r sh af ts b ase d upon collect ed field data, r anged between 1 and 6 fpm for the pum p method, and instanta neous velocit ies upwards of 40 fpm f or the bucket method. 3. 2. 2 W ait Ti me Th e w ait tim e o f a slu rry su pp ort ed bo reh ole is d ef ine d a s th e ti m e ta ke n b etw een the completion of drilli ng and concreti ng of the shaft. It is obvi ously ideal to pour the concrete di rectly a fter the dri lling is complete, however, it is e ntirel y possible for the

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47 concrete t o arrive l ater for a var iety of logist ical re asons. It i s also comm on for the co ntr act or t o p erf orm dri lli ng an d c on cre tin g o n d if fe ren t da ys If thi s is the cas e, it i s possible t o have slurr y supported bore holes left open over night. The most obvious effect of wait time is the settle ment of suspended sand in the slu rry m ixt ure A n a im of thi s te sti ng wa s to su rve y a wi de arr ay of wa it t im es t o examine the settle ment behavior. Wait times up to twelve hours were te sted. 3. 2. 3 S lu rry Pr op ert ies It was desir ed to see how different sl urry proper ties would affect the s and accumulation phenomenon. It was original ly assumed that alte ring the vol umetric sand co nte nt i nd ep en de ntl y o f s lur ry v isc os ity an d d en sit y w ou ld b e ad eq ua te f rom a re sea rch sta nd po int H ow ev er, af ter ini tia l te sts an d th e li ter atu re r ev iew it wa s f ou nd tha t th ese three pri mary characteris tics of slurr y are quite dependent on each ot her. Si nc e sl urr y d os ag e p er m an uf act ure r is giv en as a rat io o f b en ton ite we igh t to vo lum e o f w ate r, a cal ibr ati on wa s p erf orm ed to s ee h ow do sag e am ou nts wo uld af fe ct the slu rry pro pe rti es t his the sis ex am ine s. No t on ly w ou ld t his all ow fo r re sea rch ers qu ick ly o bta in d esi red pa ram ete rs, bu t al so to m ain tai n c on sis ten cy of res ult s. Ta ble 3-1 quantifies the results of this calibr ation. Table 3-1 Slurr y Dosing Cali bration

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48 If co rre lat ion be tw een slu rry pro pe rti es a nd san d s ett lem en t co uld be fo un d, it wo uld be eas y to est ab lis h c rit eri a f or c on tra cto rs t o u se t ha t di cta tes if the ne ed to c lea n ou t th e b ore ho le b ef ore co nc ret ing ex ist s. 3.3 Sand Fallout Testing Sand contents t ested were 1% 2%, 4% and 8%. This range would give researc hers adequat e information outsi de the parameters of the cur rent FDOT specificati ons. Figure 3-15 gi ves a repre sentati on of the original testing matrix for 1% sand content. In o rde r to en su re t he co ns ist en cy of tes t re su lts a sta nd ard pro ced ure wa s est ab lis he d to us e th e co nc ret e p ou r si m ula tor T he fi rst ste p in the pro ces s w as t o e ns ure the qualit y of the slurry. Slur ry was origina lly mixed by circulat ion through the pump f or the 1% and 2% s and content t ests. The lat er test s (4% and 8%) used the fan mixing de vic e. Af ter m ixi ng s tan da rd d en sit y, Mar sh co ne vis co sit y, an d s an d c on ten t te sts were run to ver ify desired sl urry proper ties. The plug was insert ed to the bott om of the shaft and, with t he winch brake applied, the shaft was filled with sl urry short ly after final mixing. After the shaft fill ed, the pu m p c on tin ue d to cir cu lat e sl urr y f or a pp rox im ate ly 5 m inu tes T he wa it t im e b eg an as soon as thi s mixing ceased. The slurr y in the shaft was is olated unti l the wait pe riod was over. After the wait per iod, the plug was pul led up by turni ng the winch at t he pre scr ibe d v elo cit y (T ab le 3 -2) an d s an d a ccu m ula tio n o n th e su rf ace of the plu g w as collect ed at the t op of the column. The accum ulation often cont ained an amount of

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49 be nto nit e, so the co lle cte d m ate ria l w as w ash ed thr ou gh a N o. 20 0 s iev e an d p lac ed in a n oven overnight t o dry. The dry material was weighe d and recorded a s sand accumulation. 3. 4 F all ou t T est in g R esu lts The sand fallout te sting was run i n sequential order from 1% to 8% sand content so the slur ry could be re cycled. 3.4.1 1% Sand Content Th e f irs t f ull ba tte ry o f t est s w ere run wi th 1 % sa nd co nte nt s lur ry w ith pro pe rti es ap pro xim ate ly i n th e m idran ge of the FD OT sp eci fi cat ion s (6 4 p cf an d 3 4 s eco nd Mar sh co ne ). T he se t est s w ere run wi th t he ori gin al p lug de sig n, wi tho ut t he pla sti c li p. Fi gu re 3-1 6 s ho ws the acc um ula tio n o f s an d f or t he arr ay of ve loc iti es a nd wa it t im es. As can be see n, the sca tte r da ta d oe s n ot s ug ge st a ny log ica l tr en ds T his ser ies of da ta p rom pte d re se ar ch er s t o r ev is e t he sa nd co ll ec ti on te ch ni qu e. It wa s a ss umed th at so me acc um ula ted san d w as e xit ing thr ou gh the dra ina ge pip e at the en d o f t he pu ll. A p las tic lip was devise d to ensure sa nd fallout would be caught and none would escape. Un fo rtu na tel y, fu rth er t est ing wi th t he ne w p lug did no t di sp lay an y a pp are nt t ren ds 3.4.2 2% Sand Content Th e 2 % sa nd co nte nt t est s co nti nu ed to u se t he ne w p lug de sig n. Th e f irs t se rie s of tes ts a t 2% we re a lso run at v ari ou s v elo cit ies T he fi rst ser ies of tes tin g u sed slu rry Ta ble 3-2 Pr esc rib ed Ve loc iti es f or H an d W inc h

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50 wi th s im ila r pr op ert ies as t he 1% s an d c on ten t te sts O nc e ag ain th e re su lts of the se t est s were unreli able. The bentonite c ontent of the slur ry was raise d, which subsequentl y led to the increase of density and viscos ity to the upper end of the FDOT specifications (66 pcf and 40 second Marsh c one). This cause d quite a difference i n the sand accumulation. Various 2% te sts are doc umented in Figure 3-17. As can be see n, the higher vi scosity, ap pro xim ate ly 4 0 s eco nd Mar sh co ne c rea tes a sl urr y m ix w he re m uc h le ss f all ou t w as ob tai ne d a s o pp os ed to t he tes ts r un wi th 3 4 s eco nd Mar sh co ne vis co sit ies T his pro m pte d re sea rch ers to c on tin ue wi th h igh vis co sit y s lur ry, as t he res ult s w ere m uc h more consistent. It w as a t th is p oin t th at t he slu rry m ixi ng de vic e w as c on str uc ted to e ns ure tho rou gh m ixi ng of the sto red slu rry pri or t o u se f or a tes t. A lso s inc e n o tr en ds wi th re sp ec t t o v el oc it y we re ap pa re nt t he te st in g mat ri x wa s r ed uc ed to co ns id er wa it ti me and sand content while using a cons tant ri sing veloci ty of two feet per minute. The remainder of the testi ng was conducted in t his manner. Figure 3-18 shows the acc um ula tio n re su lts of the ne w t est ing. Th e d ata wi th t ho rou gh ly m ixe d s lur ry i nd ica ted accumulation increa sed with wait t ime. 3.4.3 4% Sand Content The accumulation testi ng was continued on sl urry with si milar propertie s at 4% sand content. The de nsity of this sl urry was sli ghtly incr eased (to 66.5 pc f) due to the ex tra we igh t of the san d. A s im ila r pa tte rn o f a ccu m ula tio n w ith res pe ct t o w ait tim e w as expected. However, Figur e 3-19 suggests that wait t ime had no substantial e ffects on

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51 acc um ula tio n. Th is t ren d c an be ex pla ine d b y th e g ell ing be ha vio r of be nto nit e sl urr y (R ees e et al. 1 98 5). Af ter a ce rta in t im e p eri od (12 h ou rs) th e sl urr y h as b een sh ow n to gel which then ca n to suspend sand i ndefinitely. 3.4.4 8% Sand Content In an effort to examine beyond the FDOT specificati ons (4% maximum sand co nte nt) th e sa nd co nte nt w as i nc rea sed to 8 %. T he slu rry pro pe rti es w ere m ain tai ne d wi th t he ex cep tio n o f d en sit y w hic h w as a ga in s lig htl y in cre ase d (t o 6 8 p cf ) du e to ad dit ion al w eig ht o f s an d. In a n e ff ort to c atc h a ll o f t he acc um ula ted san d, a d eep er l ip was construct ed and mounted to the top of the plug. This de emed useful as the amount of san d w ou ld h av e o ve rf low n th e o rig ina l li p. Fi gu re 3 -20 sh ow s ac cu m ula tio n th at i s roughly double t hat of the 4% sand cont ent test s. It is a lso apparent that accumulation inc rea sed sli gh tly wi th w ait tim es, ho we ve r w as f air ly i ns ign if ica nt c om pa red to im m ed iat e ac cu m ula tio n. Fi gu re 3 -21 co nta ins a su m m ary of acc um ula tio n f or a ll experiments for each sand cont ent. 3.5 Sieve Analysis of Fal lout Sand Fo r ea ch tes t, a sie ve an aly sis wa s co nd uc ted on the dri ed acc um ula ted m ate ria l to determine the patt ern that gr ain sizes settle d out. It was ass umed that coarse grai ns wou ld fal l o ut qu ic kl y, fol lo we d b y fi ne r g ra in s o ve r t he pe ri od of t he hi gh er wa it ti me tests i n keeping with Stoke’ s Law (Das, 1997). Figure 322 displays t he result s of the sie ve an aly ses fo r th e 4 % sa nd co nte nt t est s co m pa red ag ain st t he ori gin al m ate ria l ad de d to the slur ry. It is apparent t hat incre asing wait t ime facilitated inc reased fallout of alm os t al l gr ain siz es. Fo r N o. 16 an d la rge r, v irt ua lly all gra ins set tle d o ut a ft er 4 ho urs

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52 For grains as small as No. 100, increasing wai t time increased fall out up to about 4 hour s. It c an be see n th at f or m ate ria ls a s f ine as N o. 20 0, m ini m al i nc rea se o ccu rre d w hic h suggests fines may remain suspended indefinite ly. Figure 3-23 depi cts the weight retaine d of each grain siz e versus si eve opening for the 4% sand cont ent test s. Also included i s the grai n size anal ysis of the tota l amount of san d in the co lum n. Th is g rap h g ive s an ind ica tio n o f t he fa llo ut p art icl es r ela tiv e to the total sand in the sl urry column. It is eas y to see the c oarser gr ained part icles fall ing ou t in a h igh er p rop ort ion to t he fi ne r m ate ria l. I t is im po rta nt t o n ote the dif fe ren ces in the sett led material bet ween tests ar e quite different. Thi s is account ed for by the sett ling of m ore co ars e g rai n p art icl es t ha n a re r ep lac ed by the ad dit ion of we llgra de d p it s an d to the slurr y. 3.6 Effect of Sand Accumulat ion Th e g rap hs of the acc um ula ted m ate ria l m en tio ne d e arl ier in t his ch ap ter us e oven-dried wei ghts to graph a gainst wait time. This was done to maintain consist ency of res ult s, bu t th is d ata req uir ed so m e re gre ssi on to e sti m ate fa llo ut i n c om m erc ial ly construct ed drill ed shafts. Si nc e sa nd is s us pe nd ed in a slur ry s olu tio n, the res ult ing de ns ity wo uld be ve ry low A loo se d ry d en sit y o f 5 0 p cf wa s as su m ed fo r sa nd in s us pe ns ion T his de ns ity all ow ed fo r ca lcu lat ion s to be m ad e to de ter m ine the tot al a m ou nt o f s an d s us pe nd ed in the slu rry du rin g a pa rti cu lar ex pe rim en tal run a s th e A PI san d c on ten t te st r ep ort s “percent by vol ume.” Since the volume of the colum n (simulated shaft) is known and the pe rce nta ge of san d in the slu rry can be de ter m ine d a s w ell th e w eig ht o f t he tot al

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53 amount of sand in the column is the percentage of volum e which is sand multipli ed by loose bulk densi ty. To verify this a ssumption, the height (vol ume) of accum ulation i n the plug was measured after an experi mental run and compared to the weight of accumulation after oven-dr ying, in this way the loose bulk de nsity was veri fied. Using the loose bul k density, Figur e 3-24 shows the sand fall out as a perc entage of tot al s an d in the slu rry co lum n. It i s ap pa ren t th at a s sa nd co nte nt o f s lur ry i nc rea ses the percent age of fallout does as well It can al so be noted that for sand contents of 4% or h igh er, wa it t im e b eco m es a sm all er f act or. Th is s ug ge sts tha t sl urr y m ixe d w ith in FD OT sp eci fi cat ion s ca n o nly ho ld a cer tai n a m ou nt o f s an d, an d th at a ft er t he cri tic al point is r eached sand will fallout regar dless of wait ti me or slurry propert ies. Figures 3-25 t hrough 3-27 depict predicte d volume and height of sand fallout drille d shafts with vari ous diameters and depths a t the FDOT m aximum limit of 4% sand content. Sand acc umulation can clearl y be seen to have a greater effect on deeper shafts. Paired with t he effects of tremie concrete dese gregating i mm ediatel y after the onset of concreti ng, this accumulation ca n have a substant ial effect on the formation of toe inclusions However, debris acc umulation at the toe c an be lifted duri ng concreti ng and deposited anywher e along the sha ft length (Figur e 1-2).

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54 Figure 3-1 Schematic Drawing of Concrete Pour Simulator Figure 3-2 Concret e Pour Simulator

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55 Figure 3-3 Int ake Plumbing Figure 3-4 Drai nage Plumbing

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56 Figure 3-5 Seal ing Device (Plug) Fi gu re 3 -6 F irs t-g en era tio n P ull ing De vic e

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57 Fi gu re 3 -7 S eco nd -ge ne rat ion Pu lli ng De vic e Figure 3-8 Slur ry Tank

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58 Fi gu re 39 Ga so li ne -p owe re d S lu rr y P ump Fi gu re 310 FDO T Dr il l R ig Pu mp

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59 Fi gu re 3 -11 Sl urr y M ixi ng De vic e Fi gu re 3 -12 Mix ing Sl urr y w ith De vic e

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60 Fi gu re 3 -13 Co nc ret e P um p T ruc k w ith Bo om Ex ten de d Fi gu re 3 -14 Tr em ie P ou r w ith Bu ck ete d C on cre te

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61 Figure 3-15 Test Matrix Fl owchart for 1% Sand Content Fi gu re 3 -16 Ac cu m ula tio n f or 1 % S an d C on ten t T est s

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62 Fi gu re 3 -17 Ac cu m ula tio n f or I nit ial 2% S an d C on ten t T est s Fi gu re 3 -18 Ac cu m ula tio n f or R ef ine d 2 % S an d C on ten t T est s

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63 Fi gu re 3 -20 Ac cu m ula tio n f or 8 % S an d C on ten t T est s Fi gu re 3 -19 Ac cu m ula tio n f or 4 % S an d C on ten t T est s

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64 Figure 3-22 Sieve Analysis for 4% Sand Content Accumulation and Pit Sand Fi gu re 3 -21 Su m m ary of Ac cu m ula tio n f or A ll S an d C on ten ts

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65 Figure 3-23 Weight Retained Vers us Sieve Opening for 4% Sand Content Fi gu re 324 Sa nd Fa ll ou t a s P er ce nt ag e o f To ta l S an d i n Co lu mn

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66 Figure 3-25 Total Volume of Sand for Various Diameter Drille d Shafts at 4% Sand Content Figure 3-26 Volume of Fallout for Various Diameter Drill ed Shafts at 4% Sand Content

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67 Figure 3-27 Depth of Fallout Versus Depth of Drilled Shaft for 4% Sand Conte nt

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68 4.0 Field Shaft Testi ng The discovery of a head di fferential in r ising mortar between t he inside and ou tsi de the rei nf orc em en t ca ge du rin g L PC tes tin g (M ull ins et a l., 20 04 ) se rie s sp aw ne d the desir e to bette r define and underst and the phenomenon. To this end, a field te sting program was established t o survey if this be havior was obser ved in full scal e drill ed shaft co ns tru cti on T he m ain ob jec tiv e o f t his tes tin g w as t o q ua nti fy he ad dif fe ren tia l behavior with va riables such as CSD (minim um clear spacing divide d by maxim um diameter of concrete coar se aggregat e), risi ng concrete ve locity, conc rete prope rties. Multipl e field visit s across se veral si tes were conduct ed to ascer tain the a mount of we t co nc ret e h ead dif fe ren tia l in va rio us typ es o f d ril led sh af t co ns tru cti on In ord er t o obtain an ass ortment of data, researc hers delibera tely chose s ites with a large var iety of shaft diameters and CSD ratios. These site vis its all owed researche rs to obtai n data for the primary objecti ve, but also t o survey comm ercial construct ion of drilled s hafts not on ly f or h igh wa y c on str uc tio n, bu t al so pri va te c on str uc tio n. Fo r ea ch sit e, res ear ch ers co lle cte d a s m uc h in fo rm ati on as p os sib le a bo ut i ts u niq ue ch ara cte ris tic s so tha t al l possible cor relati ons could be explor ed. 4. 1 P ro ced ur e At eac h o f t he sev en tee n s ite vis its d ata pe rta ini ng to s ha ft de sig n, co nc ret e m ix design, and const ruction pr ocedure were r ecorded. Rebar ca ge spacing, cage length, sh af t de pth c asi ng dia m ete r an d c on cre te d ata we re c oll ect ed reg ula rly A cu te

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69 observati on of the construct ion process was c ritic al to thi s resear ch as well, and any unusual or exce ptional pr actices were noted (e.g. c onstructi on “shortcut s”). Mo st o f t he sit es v isi ted us ed a p um p tr uc k to pla ce t he co nc ret e. Th is a llo we d for m ore consist ent data col lection s ince the pump trucks requi re similar ti mes to pum p a full concrete truck. Due to thi s construct ion procedure data was coll ected on a “by tru ck ” b asi s, wi th e ach co nc ret e tr uc k’s m eas ure m en ts t ak en ind ivi du all y a nd co un ted as its ow n d ata set H ow ev er, wh en bu ck ets we re u sed d if fe ren tia l re ad ing s w ere tak en between each bucket ful. To accuratel y determine head differential researc hers used a weight ed tape system (Figure 4-1), si milar to what drill ed shaft inspect ors use to measure ri sing co nc ret e b etw een bu ck ets or t ruc ks C om m on we igh t us ed fo r th is p roc ed ure are bro ke n dri ll a ug er t eet h. Ho we ve r, d ue to t he dy na m ics of ris ing co nc ret e, res ear ch ers fo un d th at the se w eig hts we re e asi ly c au gh t in the rei nf orc em en t ca ge an d a s a r esu lt s ev era l ta pe s were lost. Resea rchers r eplaced the auger tooth wei ght with a plumb bob m ounted upside down (Figure 4-2). Thi s allowed the wei ght to sli p past the r einforcement cage instea d of catching i t. Since thi s system was implem ented, no addit ional tape s were lost a nd consistent data coll ection was possi ble. Typically, t wo tapes were dropped be fore the first conc rete was poure d, one inside the reinforcement cage and one outs ide to take initia l heights. Duri ng pumping, he ad dif fe ren tia l re ad ing s (F igu re 4 -3) we re t ak en ev ery 30 sec on ds un til the en tir e tr uc k had been pumped into the shaft, then t he final height was measured. In be tween the 30 second measurements, the weighted tapes were kept sli ghtly above the level of risi ng

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70 co nc ret e d uri ng the po ur. Th is p roc ess wa s re pe ate d u nti l th e en tir e sh af t ha d b een po ure d. To en su re p rec ise m eas ure m en t, t he top of the tem po rar y c asi ng wa s u sed as a benchmark for both tapes. Al l si tes vis ite d u sed tem po rar y c asi ng to a id i n h ole sta bil ity ins tea d o f b en ton ite slu rry F ort un ate ly, the GW T w as e xtr em ely hig h f or a ll s ha ft s m eas ure d, wh ich clo sel y sim ula tes a w et c on str uc tio n (n atu ral slu rry ) pr oc ess typ e co ns tru cti on wi th r eg ard s to concrete pour ing. 4. 2 F iel d S ite s Researchers visited s everal si tes to col lect dat a in additi on to that col lected from Test Shaft 4 at the NGES (Auburn) si te. With the assist ance of a major drilling c ompany, res ear ch ers we re a ble to c oll ect a m ajo rit y o f t he da ta u nh ind ere d. Ea ch sit e’s construct ion will be des cribed in de tail i n the following sect ions. Figure 44 details the locations of all construc tion sit es visit ed. 4. 2. 1 P or t of Ta mp a (E sse x C eme nt ) Construction of cement silos a t Berth 219 in t he Port of Tampa f or Essex Cement Com pany demanded a foundation consisting of 177 dri lled shafts, 3 foot in di ameter. Th e sh af ts w ere dri lle d to a d ep th o f a pp rox im ate ly 7 8 f eet an d u til ize d f ull len gth tem po rar y c asi ng wi th a sid ew all thi ck ne ss o f inc h. Th e re inf orc ing cag es w ere 52 fe et in l en gth de sig ne d to ter m ina te a t th e to p o f t he roc k s oc ke t. S tir rup sp aci ng an d m ix sp eci fi cat ion s y iel de d a t C SD rat io o f a pp rox im ate ly 2 7 (m ini m um cle ar s pa cin g w as 6 inc he s an d d iam ete r of co ars e ag gre ga te w as 1 inc h). Va rio us sta ge s o f c on str uc tio n a re displayed i n Figure 4-5 and Figur e 4-6.

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71 Th e co nc ret e w as p ou red via a p um p tr uc k a nd the tre m ie r em ain ed fu lly ins ert ed in t he sh af t du rin g th e en tir e p ou r. E ach sh af t ha d a vo lum etr ic r eq uir em en t eq uiv ale nt t o tw o c on cre te t ruc ks (ap pro xim ate ly 1 5 c ub ic y ard s), slu m p w as a pp rox im ate ly 9 .5 inc he s on all sh af ts m eas ure d. Du e to the hig h w ate r ta ble v isi ble in F igu re 4 -7, we t construct ion process methods were implemented. Se ve ral iss ue s p lag ue d re sea rch ers on the fi rst sit e. La ck of an ef fi cie nt d ata rec ord ing sy ste m an d s ev era l br ok en tap es ( du e to us e o f a ug er t eet h c ou nte rw eig hts becoming lodged in cage) hinde red colle ction of all t he information available on this sit e. However, it was useful from the standpoint of refining t he data coll ection proc ess and ob ser vin g th e co m m erc ial co ns tru cti on m eth od s. Collection of 4 data sets was completed for this s ite. Figure 4-8 present s a graph of the CS D r ati o v ers us m eas ure d h ead dif fe ren tia l. I t is int ere sti ng to n ote tha t he ad dif fe ren tia ls v ari ed reg ard les s o f a co ns tan t C SD rat io. Th is s ug ge ste d th at a no the r va ria ble u pw ard ve loc ity c ou ld b e k ey in m eas uri ng we t co nc ret e b eh av ior F igu re 4 -9 pre sen ts a gra ph of up wa rd v elo cit y v ers us m eas ure d h ead dif fe ren tia l, a lth ou gh it i s difficult to deri ve any trend from such a small amount of data. 4.2.2 Crosstown Expressw ay Reversible Lanes Bridge Co ns tru cti on on the Cr os sto wn Ex pre ssw ay Re ve rsi ble La ne s B rid ge pro jec t be ga n in 20 03 (F igu re 4 -10 thr ou gh 4-1 3). Th e b rid ge is d esi gn ed to f aci lit ate thr ee l an es of traffic westward (from I-75) into Tampa during morning hours then rever se flow ea st wa rd du ri ng th e a ft er no on T he br id ge ut il iz es a mon opi er fou nd at io n s ys te m, meaning that each column rests at op a single l arge diameter dri lled shaft. The nat ure of

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72 the co ns tru cti on of thi s b rid ge w hic h w as b ein g b uil t ab ov e th e ex ist ing ele va ted Cr os sto wn Ex pre ssw ay req uir ed a la rge a m ou nt o f r ein fo rce m en t w ith tig htl y-s pa ced cag es t o re sis t ov ert urn ing m om en ts. Sh af t di am ete rs v ari ed fr om 4 to 8 f eet an d h ad de pth s o f u p to 80 fe et. CS D r ati os fo r al l sh af ts w ere 6 (m ini m um cle ar s pa cin g w as 6 inches and coar se aggregat e diameter was 1 inch) and s lumps ranged from 7 inches to 9 inches. Three shafts were i nvestigat ed at two points along the rout e that offered a significant va riati on in the const ruction at mosphere. The first two shafts (pier s 167 and 15 6) w ere 6 a nd 8 f eet in d iam ete r, r esp ect ive ly, an d lo cat ed wi thi n c los e p rox im ity to a n alr ead y e xis tin g ro ad wa y (S ite 1, Fi gu re 4 -4) T he thi rd s ha ft (pi er 1 8) w as 8 fe et i n dia m ete r an d p os iti on ed ov er t he Pa lm Ri ve r (S ite 2). Co ns tru cti on m eth od s w ere sim ila r to t ho se u sed at t he Po rt o f T am pa in t ha t a f ull len gth tem po rar y c asi ng wa s v ibr ate d to the rock la yer, the re inforcing cages wer e designed to t erminate at the r ock socket, and co nc ret e w as p um pe d f rom co nc ret e tr uc ks thr ou gh a tr em ie. Th e la rge r di am ete r sh af ts req uir ed up wa rds of 15 co nc ret e tr uc ks (ap pro xim ate ly 1 20 cu bic ya rds ) an d 5 ho urs to co m ple te, af fo rdi ng sev era l da ta s ets pe r sh af t. Fi gu re 4 -14 de pic ts C SD rat io v ers us he ad dif fe ren tia l ag ain cle arl y de m on str ati ng no dir ect co rre lat ion be tw een the se t wo va ria ble s. Pl ott ing the rec ord ed head differential against t he upward concret e velocit y, however, reveal s clear r elation for the se s ha ft s o f s im ila r C SD rat ios (F igu re 4 -15 ). T his ev ide nc e su gg est s th at p erh ap s a fa m ily of cu rve s ex ist fo r di ff ere nt r an ge s o f C SD rat ios It is e vid en t th at a no the r variable may af fect the range of head di fferential fluctuat ion within a par ticular shaft.

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73 Also observed is the incre ase in differenti al range i n shaft 167 which was twice as l arge as the range for shafts 18 and 156. W hil e w ait ing be tw een arr iva l of co nc ret e tr uc ks d if fe ren tia l m eas ure m en ts w ere tak en in t he sta gn an t bo reh ole s. In t im e p eri od s o f u p to on e h ou r, i t w as o bs erv ed tha t the wet concre te differential did not decre ase appreci ably. 4. 2. 3 A lag on Co nd omi ni um s The Alagon is a 21-st ory condominium overlooking Hil lsborough Bay (Figur e 416 thr ou gh 4-1 8). Th e f ou nd ati on of thi s lu xu rio us hig h-r ise co ns ist s o f 1 40 dri lle d sh af ts r an gin g f rom 2 to 5 f eet in d iam ete r w ith CS D r ati os of 10 (10 inc h m ini m um cle ar spacing and 1" di ameter coarse aggre gate) with s lumps ranging from 8.5 to 9 inches. Sh af t le ng ths va rie d, de pe nd en t on the e lev ati on s to roc k (2 6 to 40 fe et) T he sh af ts w ere construct ed in a similar fashion t o those of the Port of Tampa and the Crosstown Ex pr es sw ay wi th th e e xc ep ti on th at co nc re te wa s p la ce d wi th a h op pe r i ns te ad of a pu mp tru ck (F igu re 4 -17 ). T his de via tio n a ff ord ed an op po rtu nit y to ex am ine ve ry h igh up wa rd velociti es due to the r elative ly small shaft diameters and lar ge capacit y of the hopper. Di ff ere nti al h eig hts we re m eas ure d a t th e en d o f e ach bu ck et d ue to s af ety co nc ern s, the reb y a lte rin g th e m eas uri ng pro ced ure us ed wi th t he pu m p tr uc ks M os t shafts requir ed more than the theoret ical two bucket fuls (approximately 2.5 cubic yards per bucket) Since the cas ed construct ion method was used, voids within the tip of the rock socket must have opened and a llowed an amount of concrete to esc ape from the bo reh ole int o th e g eo log ica l f orm ati on be low D if fe ren tia l re ad ing s ta ke n d uri ng the se po urs rev eal ed tha t th e su rf ace of the ris ing co nc ret e ac tua lly fe ll b etw een bu ck ets in

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74 some instances. Figure 419 shows the shafts measured at Alagon t hat were not apparentl y affected by concrete l oss. Conclus ions based on thi s data cannot be made wi th a ny va lid ity du e to the ina bil ity of m eas uri ng he ad dif fe ren tia l du rin g th e ac tua l bu ck et p ou r. H en ce, the da ta o bta ine d w as d isc ou nte d f or t he pu rpo ses of dif fe ren tia l data. 4. 3 He ad Di ffe ren tia l S um mar y Fi gu re 4 -20 su m m ari zes the he ad dif fe ren tia l da ta f rom the Po rt o f T am pa Cr os sto wn a nd the NG ES sit e (d if fe ren tia l da ta w as o bta ine d v ia v ide o f or s ha ft TS -4) as a function of the CSD. Clearly, the CSD is not t he only parameter affecting the buildup of co nc ret e h ead ins ide the rei nf orc ing cag e. Fi gu re 4 -21 sh ow s th e sa m e d ata as a function of velocity for eac h group of comm on CSDs observed. A second order t rends ap pe ar t o e xis t f or d if fe ren t C SD va lue s, ve rif yin g th e co nc ep t th at h ead pre ssu re i s dir ect ly p rop ort ion al t o th e sq ua re o f t he ve loc ity he ad G ive n a co ns tan t up wa rd velocity, a drastic difference in head differenti al occurs a s the CSD increases from 6 to 8; once the CSD increase s beyond 8, the head di fferential is much less si gnificant for high ve loc iti es. It s ho uld be no ted tha t th e h ead dif fe ren tia l in the Cr os sto wn dri lle d s ha ft s d id no t a pp re ci ab ly de cr ea se du ri ng wa it ti me be tw ee n c on cr et e t ru ck s, de sp it e h ig h s lu mp concrete. Since there are few alterna te configurati ons for a given rei nforcement cage design an d c on cre te f low rat e is hig hly un co ntr oll ab le, it i s m ore rat ion al t o a dju st t he co ars e ag gre ga te s ize so as t o m ini m ize co nc ret e b uil d-u p in sid e th e ca ge T his m ini m iza tio n is preferable gi ven the ease wit h which a thick l ayer of sediment can be deposit ed at sand

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75 contents appr oaching 4%. There fore, using the re sults shown in Figur e 4-21, any set of he ad dif fe ren tia l da ta a t a c on sta nt v elo cit y w ill sh ow the CS D l im it b elo w w hic h s ho uld be avoided. Figure 4-22 shows that a minimum CSD of 8 is recom mended. The FD OT ha s al rea dy tak en ste ps to r eco m m en d a m ini m um CS D o f 1 0 a s a r esu lt o f t his pro jec t’s findings.

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76 Figure 4-1 Weighted Tape for Differential Measurement Figure 4-2 Plumb-bob Counterweight

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77 Figure 4-3 Researchers Taking Head Differential Measurements Figure 4-4 Map of Head Differential Measurement Sites

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78 Figure 4-5 Drilled Shaft Construction at the Port of Tampa Figure 4-6 Cage Installation at Port of Tampa (Large Clear Spacing)

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79 Figure 4-7 View of Shaft before Pour at Port of Tampa (GWT at 6 Feet Below Grade) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 051015202530 CSD (in/in)Head Differential (ft.) Shaft 1 Shaft 2Figure 4-8 CSD Ratio Versus Head Differential for Port of Tampa

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80 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 012345 Upward Velocity (ft/min)Head Differential (ft.) Shaft 1 Shaft 2Figure 4-9 Upward Velocity Versus Head Differential for Port of Tampa Figure 4-10 Drilled Shaft Construction at the Crosstown Expressway

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81 Figure 4-11 Cage Installation at the Crosstown Expressway (Small Clear Spacing) Figure 4-12 Head Differential Measurements at Crosstown Expressway

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82 Figure 4-13 Visible Concrete Inside the Reinforcement Cage During End of Pour at Crosstown Expressway (Mono-pier Cage Construction) 0 0.5 1 1.5 2 2.5 3 01234567CSD (in/in)Head Differential (ft.) Shaft No. 156 Shaft No. 18 Shaft No. 167Figure 4-14 CSD Ratio Versus Head Differential for Crosstown Expressway

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83 0 0.5 1 1.5 2 2.5 3 00.511.52 Upward Velocity (ft/min)Head Differential (ft.) Shaft No. 156 Shaft No. 18 Shaft No. 167Figure 4-15 Upward Velocity Versus Head Differential for Crosstown Expressway Figure 4-16 Drilled Shaft Construction at Alagon Condominiums

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84 Figure 4-17 Bucket Pour at Alagon Condominiums Figure 4-18 Researcher Taking Concrete Depth Measurements at Alagon

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85 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0510152025303540 Upward Velocity (ft/min)Head Differential (ft.)Figure 4-19 Upward Velocity Versus Head Differential for an Alagon Shaft 0 0.5 1 1.5 2 2.5 3 0102030405060708090 Clear Space to Diameter Ratio, CSD (in/in)Head Differential (ft.) Lab Data (Garbin, 2003) NGES Data (TS-4) Port of Tampa Crosstown Expressway 1/2 Inch Cage 1/4 Inch Cage 1 Inch CageFigure 4-20 Summary of CSD Ratio Versus Head Differential for All Sites and Lab Data

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86 0 0.5 1 1.5 2 2.5 3 3.5 4 012345 Velocity (ft/min)Head Differential (ft.) Crosstown Data Port of Tampa Data TS-4 (Auburn) CSD = 6 CSD = 8 CSD = 26 Figure 4-21 Summary of Velocity Versus Head Differential Data for All Sites 0 0.5 1 1.5 2 2.5 051015202530 CSD (in/in)Head Differential (ft @ 1.5 ft/min) Recommended CSD Range ( > 8) FHWA Recommended Minimum CSD (3 5) CSD = 6 CSD = 8 CSD = 26 H V See Figure 4-21Figure 4-22 Recommended CSD Range for Drilled Shaft Construction

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87 5.0 Conclusions and Recommendations Th e o rig ina l ba sis fo r th is r ese arc h s tem m ed fr om an om aly fo rm ati on s in dri lle d shafts (such as s oil incl usions) tha t had been noted t o occur in the vicinit y of the gro un dw ate r ta ble (G W T) ele va tio n. Al tho ug h n ot f ou nd to b e d ire ctl y c orr ela ted to inclusion pot ential, t he GW T does affect wet method construction by i nfluencing the borehole st abilit y. To this end, the pr oject was expande d and examinations of sediment su sp en sio n in be nto nit e sl urr y, as w ell as c on cre te f low be ha vio r w ere co nd uc ted wi th regards t o anomaly form ation. This t hesis focused on thes e later parameters. Concerning sand set tlement, four series of test ing were conducte d with the concrete pour simulator. The variabl es of these test s were wait ti me, upw ard (ri sing co nc ret e) v elo cit y, an d s lur ry p rop ert ies (e. g. de ns ity v isc os ity s an d c on ten t). Th e f irs t ser ies of tes ts w ere car rie d o ut o n s lur ry w ith 1% s an d c on ten t, a nd de m on str ate d th at up wa rd v elo cit y in du ced lit tle ef fe ct o n s an d s ett lem en t. T he sec on d s eri es w ere conducted on slur ry with 2% sand c ontent and demonstrated t hat low viscosi ty (32 second Marsh c one) slurr y had much higher sand fallout rel ative to hi gh viscosit y (39-42 sec on d M ars h c on e). Sl urr y w ith 4% s an d c on ten t w as t est ed in t he thi rd s eri es, wh ich sh ow ed wa it t im e h ad lit tle ef fe ct o n s ett lem en t, a s re lat ive ly e qu al f all ou t w as o bs erv ed for wait times of up to 12 hours. The slurr y used in the final series ha d a sand content of 8%, an d c on fi rm ed the tre nd of co ns ist en t f all ou t re ga rdl ess of wa it t im e. It w as a lso apparent t hat, as sand cont ent incre ased, the amount of fallout relat ive to the t otal amount

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88 of san d a lso inc rea sed It wa s d isc ov ere d th at u na git ate d s lur ry i n th e co lum n (b ore ho le) wi ll s ett le m os t m ate ria l w ith in t he fi rst tw o h ou rs. In s om e in sta nc es, thi s am ou nt w as shown to be as high as 50% of the total amount of sand in the col umn. Co nc ern ing the fi eld res ear ch o ve r 40 set s o f d ata we re t ak en in f ull -sc ale d s ha ft s at t hre e co ns tru cti on sit es. Th is t est ing wa s co nd uc ted to q ua nti fy he ad dif fe ren tia l as a fu nc tio n o f C SD rat io, ris ing co nc ret e v elo cit y, an d w et c on cre te p rop ert ies T he fu ll scale te sting showed that the CSD ratio did not directl y correla te with head di fferential. Ins tea d, it w as f ou nd tha t as up wa rd v elo cit y in cre ase d, lar ge r he ad dif fe ren tia ls w ere ob ser ve d. It w as a lso ap pa ren t th at s ha ft s w ith sim ila r C SD rat ios sh ow ed sim ila r he ad dif fe ren tia ls w ith res pe ct t o v elo cit y. Th e la rge st h ead dif fe ren tia ls ( up wa rds of 2. 5 f eet ) we re o bs erv ed fo r sh af ts w ith CS D r ati os of ap pro xim ate ly 6 A s th e C SD rat io inc rea sed th e h ead dif fe ren tia l di d s o a s w ell H ead dif fe ren tia l m eas ure m en ts t ak en during wait t imes between concrete t rucks revea led minim al decrea se occurre d for pe rio ds of up to o ne ho ur. Th is s ug ge sts tha t, i n c on jun cti on wi th r ap id s an d f all ou t, inc lus ion s m ay fo rm wh en po uri ng res um es, tra pp ing set tle d m ate ria l in the co nc ret e cover area s. Ba sed on the co nc lus ion s d eri ve d in thi s th esi s, rec om m en da tio ns fo r ch an ge s in pe rti ne nt s ect ion s o f t he FD OT St an da rd S pe cif ica tio ns are as f oll ow s: (I) CS D> 8. Cu rre nt F HW A r eco m m en da tio ns su gg est tha t a C SD rat io a s low as 3 is r eas on ab le. Ho we ve r, c on cre te f low ob ser ve d (F igu re 5 -1) in thi s th esi s su pp ort an inc rea se i n th is r eco m m en de d v alu e. Th is a pp lie s to structur al, geotechni cal, and materials engineers a like. As the si ze and

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89 configuration of rebar in drill ed shaft cages cannot always be alt ered, sm all er m ax im um ag gre ga te d iam ete r m ay be ap pro pri ate S m all er s ize d co ars e ag gre ga te, su ch as # 7 s ton e, sh ou ld b e co ns ide red fo r tr em iepla ced drille d shaft construct ion. This would help t o increase the CSD and the reb y lo we r th e p ote nti al h ead dif fe ren tia l th at c ou ld d ev elo p. Th is m ean s le ss c on cre te b ack pre ssu re w ou ld b e n eed ed to a de qu ate ly penetrat e the cage. Where practi cal, this limit should be appli ed to the worst case spa cing in the c age, such as spl iced cage se gments. (II) Slurry sand cont ent < 1%. When constructi ng shafts using slur rydisplacement constr uction, the s and content at the time of concreting should be reduce d to a more restric tive value of 1% from the present value of 4%. The concrete pour simulator used in thi s thesis s howed that lar ge am ou nts of san d c an be su sp en de d in the slu rry bu t an alm os t eq ua l amount can fall out of suspension within t he first 2 hours ( e.g. a 60 foot deep excavati on at 4% sand cont ent would fallout 38% of total sand, or 11 inc he s o f a ccu m ula tio n). Fu rth er, oth er S ou the ast ern sta tes ha ve rec en tly adopted similar re quirements. This can be met by either de-sanding or by maintaining two separat e slurry t anks, one with cle an concreti ng slurry, an d a sec on d w ith ex cav ati ng slu rry T he ex cav ati ng slu rry is t he n ex ch an ge d w ith the co nc ret ing slu rry pri or t o th e st art of the po ur. Sl urr y condition dur ing drill ing is les s criti cal with re gard to sand cont ent pro vid ed tha t su ff ici en t sl urr y h ead ab ov e th e G W T i s m ain tai ne d. Fa ilu re

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90 to m ain tai n a sta ble bo reh ole res ult s in slo ug hin g a nd a re du cti on in s oil str en gth In su ch cas es, the an tic ipa ted de sig n c ap aci ty i s u nre lat ed to actual ca pacity. Fu rth er t op ics of stu dy inc lud e th e co nti nu ed de ve lop m en t of a f am ily of cu rve s to correla te upward veloci ty in shafts with s imilar CSD ratios to head di fferential. Also, the po ten tia l re lat ion sh ip b etw een rad ial ve loc ity of co nc ret e in the sh af t ve rsu s th e h ead dif fe ren tia l sh ou ld b e in ve sti ga ted T his wo uld fu rth er q ua nti fy the ph en om en on of he ad dif fe ren tia l an d a llo w d esi gn ers to c rea te d ril led sh af ts w hic h n ot o nly ha ve ad eq ua te str en gth b ut a lso eas ily co ns tru cta ble wh ile m ini m izi ng the ch an ce o f a no m aly form ation. Figure 5-1 Behavior of Rising Concret e in Tremie Poured Drille d Shaft

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91 Re fer en ces Association of Dril led Shaft Contractor s (ADSC) W ebsite ( 2004). htt p:/ /w ww .a ds c-i af d. co m /hi sto rypa ge .h tm l. As so cia tio n o f D ril led Sh af t C on tra cto rs ( 20 04 ). S lur ry S ch oo l C on fe ren ce. De nv er, Colorado, October 79th. Be res fo rd, J. J. C ash m an P .M ., an d H oll am by R .G (1 98 9). “T he Mer its of Po lym eri c Fl uid s as Su pp ort Sl urr ies .” Proceedings of t he Internat ional Conference on Piling and Deep Foundations A.A. Balkem a, Rotterdam. Be rko vit z, B. (19 95 ). “ Us e o f P oly m er S lur rie s f or D ril led Sh af t C on str uc tio n. ” Symposium on Engineering Geology and Geot echnical Engine ering. Logan, Utah. Br ow n, D. (20 02 ). “ Ef fe ct o f C on str uc tio n o n A xia l C ap aci ty o f D ril led Fo un da tio ns in Pi ed m on t S oil s. ” Journal of Geotec hnical Engineer ing Vol. 128, No. 12. Brown, D. (2004). “Zen and the Art of Drill ed Shaft Construction: The Pursuit of Qu ali ty. ” Geosupport Conference: Innovation and Cooperat ion in the Geoindustry, Dril led Shafts, M icropili ng, Deep Mixing, Remedial Methods, and Specialty Foundation Systems. Am erican Soci ety of Civil Engineer s, Reston, VA. Br ow n D ., Mu ch ard M ., an d K ho uri B (2 00 2). “T he Ef fe ct o f D ril lin g F lui d o n A xia l Ca pa cit y, Ca pe Fe ar R ive r, N C. ” Deep Foundations: the Time Factor in Design an d C on str uc tio n o f D eep Fo un da tio ns Deep Foundations Inst itute, 25. Ca en n, R. C hil lin ga r, G (1 99 6). “D ril lin g f lui ds : S tat e o f t he art .” Journal of Petr oleum Science and Enginee ring. Vol. 14, No. 3. California Depart ment of T ransporta tion. (1997). California Foundati on Manual. Sacramento, CA: CALT RANS. Ce rna k, B. (19 76 ). “ Th e T im e E ff ect of Su sp en sio n o n th e B eh av ior of Pi ers .” 6 th European Conference on Soil Mechanics and Foundat ion Engineering. Vi en na Au str ia.

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92 Das, Braja M. (1997) “Soil Mechani cs Laborator y Manual.” 5 Edition, Austin, TX: th En gin eer ing Pr ess Fe de rat ion of Pi lin g S pe cia lis ts. (19 75 ). “ Sp eci fi cat ion s f or C ast in P lac e P ile s F orm ed un de r B en ton ite Su sp en sio n. ” Ground Engineering Vol. 8, No. 2, London, England. Fleming, W .K. and Sliwinski, Z.J. (1977) Th e U se a nd Inf lue nc e o f B en ton ite in B or ed Pile Construct ion. London, England: CIRIA Report PG3. Florida Depart ment of T ransporta tion. (1987 and 2000) Se cti on 45 5: S tru ctu res Fo un da tio ns Tallahasse e, FL: FDOT. Garbin, E.J. (2003). The Influence of Water Tabl e in Drille d Shaft Construct ion Doctoral Disse rtati on, University of South Flor ida, Tampa, FL. Holden, J.C. (1983). “The Construc tion of Bored Piles i n W eathered Sedi mentary Rock.” Fo ur th A us tra lia n-N ew Ze ala nd Co nfe ren ce o n G eo me ch an ics P ert h, Au str ali a, May. Hutchinson, M.T., Daw, G.P., Shotton, P.G., and James, A.N (1975). “The Proper ties of Be nto nit e S lur rie s U sed in D iap hra gm W all ing an d th eir Co ntr ol. ” Diaphragm Wal ls a nd An ch or ag es London, England. Maj an o, R. E. O ’N eil l, M .W ., an d H ass an K .M (1 99 4). “P eri m ete r L oa d T ran sf er i n Mo de l D ril led Sh af ts F orm ed un de r S lur ry. ” Journal of Geotec hnical Engineering. Vol. 120, No. 12. Mullins, A.G. and Ashmawy, A.K (2004). Fa cto rs A ffe cti ng An om aly Fo rm ati on in Dr ill ed Sh aft s. University of South Flor ida report to the FDOT. Na sh K .L (1 97 4). “S tab ili ty o f T ren ch es F ill ed wi th F lui ds .” Journal of the Construction Engine ering Divisi on A m eri can So cie ty o f C ivi l E ng ine ers V ol. 100, No. CO4. O’Neill, M.W. and Reese, L.C. (1992). “Behavior of Axially Loade d Drilled Shafts i n Beaumont Clay.” Report No. 89-8, The University of Texas at Austin. O’Neill, M.W. and Reese, L.C. (1999). Drilled Shaft s: Constructi on Procedures and Design Methods Vol ume 1. Dallas, TX: ADSC: The Internat ional Associa tion of Foundation Drill ing. Passe, P.D. (1993). “Dril led Shaft Inspect ors Manual” Florida Depart ment of Transportat ion. C-1.

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93 Re ese L .C a nd Tu ck er, K. L. (19 85 ). “ Be nto nit ic S lur ry i n C on str uc tin g D ril led Pi ers .” Dr ill ed Pi ers an d C ais so ns II N ew Yo rk, NY : A m eri can So cie ty o f C ivi l Engineers. St eb bin s, E. E. an d W ill iam s, R. C. (19 86 ). “ W etHo le D ril led Sh af t C on str uc tio n. ” Drilled Shaft Foundati on Seminar, Atlanta, GA, February 19-20. Th as na ni pa n, N., Ba sk ar an G. a nd Anw ar M .A. (1 99 8) “ Effe ct of C on st ru ct io n T ime an d B en ton ite Vi sco sit y o n S ha ft Ca pa cit y o f B ore d P ile s, ” Pr oc eed ing s o f th e 3 rd Int ern ati on al G eo tec hn ica l Se mi na r o n D eep Fo un da tio ns on Bo red an d A ug er Piles. Ghent, Belgium.

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94 Ap pe nd ice s

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95 Ap pe nd ix A : T ab ul ar La bo ra tor y D ata A. 1 A ccu mu lat ion Te sti ng Da ta Table A-1 1% Sand Content Table A-2 Init ial 2% Sand Content Table A-3 Refined 2% Sand Content

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96 Appendix A: (Continued) A. 2 S iev e A na lys is D ata Table A-4 4% Sand Content Table A-5 8% Sand Content Ta bl e A -7 2% Sa nd Con te nt 1 Hou r Wa it Ti me Ta bl e A -6 2% Sa nd Con te nt No Wai t T ime

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97 Appendix A: (Continued) Ta bl e A -8 2% Sa nd Con te nt 2 Hou r Wa it Ti me Ta bl e A -9 2% Sa nd Con te nt 4 Hou r Wa it Ti me Ta bl e A -1 0 2 % S an d Co nt en t, 12 Hou r Wa it Ti me

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98 Appendix A: (Continued) Ta bl e A -1 2 4 % S an d Co nt en t, 1 Ho ur Wai t T ime Ta bl e A -1 1 4 % S an d Co nt en t, No W ai t T ime Ta bl e A -1 3 4 % S an d Co nt en t, 2 Ho ur Wai t T ime

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99 Appendix A: (Continued) Ta bl e A -1 5 4 % S an d Co nt en t, 12 Hou r Wa it Ti me Ta bl e A -1 4 4 % S an d Co nt en t, 4 Ho ur Wai t T ime Ta bl e A -1 6 8 % S an d Co nt en t, No Wa it Ti me

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100 Appendix A: (Continued) Ta bl e A -1 7 8 % S an d Co nt en t, 1 Ho ur Wai t T ime

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101 Ap pe nd ix B : C oll ect ed Fi eld Da ta B. 1 P or t of Ta mp a (E sse x C eme nt ) Ta ble B1 P ort of Ta m pa Sh af t D ata Table B-2 Measur ed Head Differentials for the Port of Tampa

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102 Appendix B: (Continued) B.2 Crosstown E xpressway Table B-3 Crosstown Expressway Shaft Data (No. 156) Table B-4 Crosstown Expressway Shaft Data (No. 18) Table B-5 Crosstown Expressway Shaft Data (No. 167)

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103 Appendix B: (Continued) Table B-6 Measur ed Head Differentials for Crosst own Expressway (Shaft No. 156)

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104 Appendix B: (Continued) Table B-7 Measur ed Head Differentials for Crosst own Expressway (Shaft No. 18)

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105 Appendix B: (Continued) Table B-8 Measur ed Head Differentials for Crosst own Expressway (Shaft No. 167)

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106 Appendix B: (Continued) B. 3 A lag on Co nd omi ni um s Ta ble B9 A lag on Sh af t D ata Ta ble B10 He ad Di ff ere nti al Data for Alagon Shaft


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Slurry sand content and concrete interaction in drilled shaft construction
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ABSTRACT: Due to the widespread use of drilled shafts in state and federal highway bridges, strict regulation of the design and construction has been imposed by the respective agencies. However, documented cases of anomalies and/or poorly performing shafts continue to arise. To this end, this thesis investigates several aspects of drilled shaft construction that may affect the quality of the finished product. These areas include bentonite slurry properties and performance as well as reinforcement cage and concrete flow interactions. Recent research indicates tremie poured concrete does not flow as predicted. Instead of even rising, a differential between the height of concrete inside and outside the reinforcement cage has been observed.Compounding this problem is the fact that bentonite slurry used to support boreholes may settle suspended sand at the toe of the shaft or on the surface of rising concrete during long wait periods, affording the possibility of soil inclusions in the shaft. This thesis examines two methods of inquiry to quantify the behavior of concrete in a tremie pour drilled shaft and sand suspension behavior of bentonite slurry. Conclusions and recommendations are made to improve pertinent construction regulations to ensure quality of drilled shafts.
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