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A study on the calibration and accuracy of the one-step TDR method

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Title:
A study on the calibration and accuracy of the one-step TDR method
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English
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Runkles, Brian David
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University of South Florida
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Water content
Dry density
Dielectric constant
Electrical conductivity
Nuclear
Dissertations, Academic -- Civil Engineering -- Masters -- USF
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bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

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Abstract:
ABSTRACT: Traditional in-situ soil compaction monitoring methods are often limited in their application, thus quality control of compacted fills and roadway embankments remains a challenging problem. As a result, new methods are being developed to more accurately measure in-situ compaction parameters. Time domain reflectometry (TDR) is one such method. Several advances have been made over the past few years to further the use of TDR technology in water content and density measurement of compacted fill. The one-step method relies on the measurement of the apparent dielectric constant in conjunction with the bulk electrical conductivity, and correlates them through two soil-specific constants, f and g. The two measurements, together with other soil specific constants, are then used to back calculate the water content and density in a single step. However, questions remain regarding the accuracy and bias of TDR measurements in relation to other "established" in-situ procedures such as the nuclear gage and speedy moisture. Results from an experimental program to obtain calibration constants for typical sands used in roadway construction are presented. A number of side-by-side tests are performed to compare the measurements obtained using the TDR one-step method to those obtained form other methods. Conducting such side-by-side tests is a critical step in the progress and eventual widespread usage of the one-step method. In addition, all the results are compared against an independent measurement of the in-place density from a slurry-replacement method. The objective of the independent measurement is to provide a baseline for accurate and unbiased evaluation of TDR and other technologies.
Thesis:
Thesis (M.A.)--University of South Florida, 2006.
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Includes bibliographical references.
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by Brian David Runkles.
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Title from PDF of title page.
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A Study on the Calibration and Accuracy of the One-Step TDR Method by Brian David Runkles A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering Department of Civil and Environmental Engineering College of Engineering University of South Florida Major Professor: Alaa K. Ashmawy, Ph.D. Gray Mullins, Ph.D. Rajan Sen, Ph.D. Date of Approval: July 14, 2006 Keywords: water content, dry density, dielectri c constant, electrical conductivity, nuclear Copyright 2006, Brian David Runkles

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DEDICATION This work is dedicated to my pare nts. For withou t their patience, understanding, support, and most of all their love the co mpletion of this thesis would not have been possible.

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ACKNOWLEDGEMENTS I would like to thank my advisor, Dr. Alaa Ashmawy, for providing me with the opportunity to work on this project. Y our guidance and mentorship are greatly appreciated. I truly could not have asked for a better person to have worked under. Also, the Florida Department of Transpor tation should be thanked for supporting my research efforts through a research grant to the University of South Florida. I would like to express my sincere appreciation to the State Materials Office personnel in Gainesville for thei r continuous support th roughout the course of the project. In specific, the help of Dr. David Horhota, Mr. Ronnie Lewis, Mr. Rick Venick, and Mr. Bruce Swidarski is acknowledged. Additional thanks goes to the members of my examining committee, Dr. Gray Mullins and Dr. Rajan Sen, the faculty and staff of the Civil and Environment Engineering Department, and to my colle ges and friends for contributing to the development of this thesis.

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i TABLE OF CONTENTS LIST OF TABLES............................................................................................................iv LIST OF FIGURES.............................................................................................................v ABSTRACT....................................................................................................................vii i CHAPTER 1 – INTRODUCTION.....................................................................................1 Background.............................................................................................................1 Organization of Thesis............................................................................................2 CHAPTER 2 – LTERATURE REVIEW............................................................................3 Evolution of Time Domain Reflectometry..............................................................3 Basic Principles of Time Domain Reflectometry...................................................4 Development of the ASTM TDR Measurement System........................................4 Basic Principle of the One-Step TDR Method........................................................6 Determining the Apparent Dielectric Constant, Ka.................................................6 Determining the Bulk Electric Conductivity, ECb..................................................8 Calibration Relationship for Soil A pparent Dielectric Constant.............................9 Calibration Relationship for Bulk Soil Electrical Conductivity............................10 Dielectric Constant Bulk Elec trical Conductivity Relationship.........................11 Data Reduction Process to Obtain Water Content and Dry Density.....................12 CHAPTER 3 – TDR EQUI PMENT AND PROCEDURE...............................................14 Introduction...........................................................................................................14 TDR Measurement System...................................................................................14 Tool Case, Electronics Case, Wiring of the TDR System....................................17 Case 1 – TDR Tool Case...........................................................................17 Case 2 – TDR100 Sample, Batte ry, Charger, and Laptop.........................17 TDR Software (PMTDR-SM)...............................................................................19 Testing Procedure..................................................................................................21 Apparatus Calibration................................................................................21 Laboratory Test..........................................................................................22 In-situ Test.................................................................................................26

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ii CHAPTER 4 – EVALUATION OF TDR CONSTANTS................................................30 Introduction...........................................................................................................30 Calibration Constants “ a ” and “ b ”........................................................................30 Calibration Constants “ c ” and “ d ”........................................................................32 Calibration Constants “ f ” and “ g ”.........................................................................33 Calibration Testing Program.................................................................................34 Calibration Test Results........................................................................................34 Results and Discussion for “ a ” and “ b ”.....................................................34 Results and Discussion for “ c ” and “ d ”.....................................................36 Results and Discussion for “ f ” and “ g ”......................................................38 Parametric Study on Soil Ca libration Constants...................................................39 Effects of “ b ” on Water Content and Dry Density....................................39 Effects of “ d ”on Water Content and Dry Density.....................................40 Summary...............................................................................................................41 CHAPTER 5 – TDR COMPARED TO TRADITIONAL METHODS............................42 Introduction...........................................................................................................42 Testing Program....................................................................................................43 Test Results...........................................................................................................43 Water Content Measurement Discussion..............................................................50 Dry Density Discussion.........................................................................................50 Measurement Variability Study............................................................................51 Summary...............................................................................................................53 CHAPTER 6 – SLURRY REPLACEMENT METHOD..................................................54 Introduction...........................................................................................................54 Principle................................................................................................................54 Equipment.............................................................................................................55 Equipment Fabrication and Calibration................................................................56 Slurry Viscosities for Di fferent Sand Gradations.................................................56 Testing Procedure..................................................................................................58 Calculations...........................................................................................................60 Experimental Verification of Measurement Accuracy..........................................61 Concrete Control Volume Assembly.........................................................61 Concrete Control Volume Tests................................................................62 Soil Control Volume Assembly.................................................................63 Soil Control Volume Test..........................................................................65 Slurry Replacement Calibration Test.........................................................65 Experimental Verification Results and Discussion...............................................69 Field Testing Program...........................................................................................71 Field Test Result and Discussion..........................................................................72 Summary...............................................................................................................75

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iii CHAPTER 7 – SUMMARY, CONCLU SIONS, AND RECOMMENDATIONS...........76 Summary...............................................................................................................76 Conclusions...........................................................................................................76 Recommendations.................................................................................................78 REFERENCES..................................................................................................................79 BIBLIOGRAPHY.............................................................................................................83

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iv LIST OF TABLES Table 4-1. TDR Soil Consta nts for Florida Sands......................................................35 Table 4-2. Calibration of TDR Soil Constant “ c ”.......................................................38 Table 5-1. Testing Locations and Information............................................................43 Table 5-2. Speedy Water Content Comparison Results..............................................44 Table 5-3. Nuclear Water Content Comparison Results.............................................45 Table 5-4. Dry Density with Speedy Comparison Results..........................................47 Table 5-5. Dry Density with Nuclear Comparison Results.........................................48 Table 5-6. Testing Loca tions and Measurements........................................................52 Table 6-1. Slurry Mix Ratios Based on Soil Type......................................................58 Table 6-2. Results of Slurry Replacement Calibration Test........................................70 Table 6-3. Testing Locations and Information............................................................72 Table 6-4. Dry Density Comparison Results...............................................................72 Table 7-1. Recommended Values of TDR Calibration Constants..............................78

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v LIST OF FIGURES Figure 2-1. Purdue TDR Measurement System..............................................................5 Figure 2-2. Typical TDR Wave Reflection....................................................................7 Figure 2-3. Electrical C onductivity Wave Analysis.......................................................9 Figure 2-4. Adjusting the Field Samp le to the Laboratory Calibration........................13 Figure 3-1. TDR System Configuration.......................................................................14 Figure 3-2. Configuration of Coaxial Head..................................................................15 Figure 3-3. The Coaxial Cyli nder (CC) Transmission Line.........................................16 Figure 3-4. The Multiple Rod Probe (MRP)................................................................16 Figure 3-5. TDR Tool Case..........................................................................................17 Figure 3-6. TDR Electronics Case................................................................................18 Figure 3-7. Layout of th e TDR Electronics Case.........................................................18 Figure 3-8. In-situ MRP Input Screen..........................................................................20 Figure 3-9. CC Mold Test Input Screen.......................................................................21 Figure 3-10. Compacting the Cylindrical Mold.............................................................23 Figure 3-11. Central Spike Driven Through the Guide and into the Sample.................23 Figure 3-12. Taking the TDR Measurement...................................................................24 Figure 3-13. Example Calibration for “ a ” and “ b ”.........................................................25 Figure 3-14. Example Calibration for “ c ” and “ d ”.........................................................26 Figure 3-15. Example Calibration for “ f ” and “ g ”..........................................................26 Figure 3-16. Driving Spikes through Template into Soil...............................................27 Figure 3-17. Removal of the Template...........................................................................28 Figure 3-18. Placement of Coaxial Head (CH) on Spikes..............................................28 Figure 4-1. Individual Calibration Points for Obtaining “ a ” and “ b ”...........................36 Figure 4-2. Individual Calib ration Points for Obtaining “ c ” and “ d ”...........................37

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vi Figure 4-3. Individual Calib ration Points for Obtaining “ f ” and “ g ”...........................39 Figure 4-4. Parametric Study on Soil Constant “ b ”......................................................40 Figure 4-5. Parametric Study on Soil Constant “ d ”......................................................41 Figure 5-1. Speedy Versus ASTM TDR Water Content..............................................46 Figure 5-2. Nuclear Versus ASTM TDR Water Content.............................................46 Figure 5-3. Speedy Nuclear Ve rsus ASTM TDR Dry Density....................................49 Figure 5-4. Nuclear Vers us ASTM TDR Dry Density.................................................49 Figure 5-5. Water Content Variability Within a Site....................................................52 Figure 5-6. Dry Density Va riability Within a Site.......................................................53 Figure 6-1. Assembly of Equipment for Slurry Replacement......................................55 Figure 6-2. Test Cell Filled with Sand..........................................................................57 Figure 6-3. Test Cell with Slurry on Top of Sand........................................................57 Figure 6-4. Slurry Level Monitoring............................................................................57 Figure 6-5. Level and Smooth the Soil Surface............................................................59 Figure 6-6. Soil Excavation Process.............................................................................59 Figure 6-7. Pour Slurry Through Base-plate Hole........................................................59 Figure 6-8. Concrete Control Volume..........................................................................62 Figure 6-9. Concrete Contro l Volume Test Equipment................................................62 Figure 6-10. Control Box with Extension Collar............................................................63 Figure 6-11. Fiberglass Resin, Material, and Tools........................................................64 Figure 6-12. Control Box Corner Detail.........................................................................64 Figure 6-13. Soil Mixed with Water...............................................................................65 Figure 6-14. Compacting the Soil in the Box.................................................................66 Figure 6-15. Compacted Soil with Extension Collar Removed.....................................66 Figure 6-16. Trimming the Excess Soil..........................................................................66 Figure 6-17. Control Box Fille d with Soil and Trimmed Flush.....................................67 Figure 6-18. Lifting the Soil Fille d Box Using the Over-head Hoist.............................67 Figure 6-19. Weighing the Box After Filling.................................................................68 Figure 6-20. Slurry Replacement Proce dure on Soil Control Volume Calibration........69

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vii Figure 6-21. Slurry Replacemen t Density Versus Actual Density.................................71 Figure 6-22. Side-by-Side Testing..................................................................................71 Figure 6-23. Nuclear and TDR Density Versus Slurry Replacement Density...............73 Figure 6-24. Hypothesis Validation Plot........................................................................74 Figure 6-25. Slurry Viscosity Base d on Effective Particle Size D10..............................75

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viii A STUDY ON THE CALIBRATIO N AND ACCURACY OF THE ONE-STEP TDR METHOD Brian David Runkles ABSTRACT Traditional in-situ soil compaction mon itoring methods are often limited in their application, thus quality cont rol of compacted fills and roadway embankments remains a challenging problem. As a result, new methods are being developed to more accurately measure in-situ compaction parameters. Time domain reflectometry (TDR) is one such method. Several advances have been made ove r the past few years to further the use of TDR technology in water content and density measurement of compacted fill. The onestep method relies on the measurement of the apparent dielectric c onstant in conjunction with the bulk electrical conductivity, and correlates th em through two soil-specific constants, f and g The two measurements, together with other soil specific constants, are then used to back calculate the water content and density in a single step. However, questions remain regarding the accuracy and bias of TDR measurements in relation to other “established” in-situ pr ocedures such as the nuclear gage and speedy moisture. Results from an experimental program to obt ain calibration constants for typical sands used in roadway construction are presente d. A number of side -by-side tests are performed to compare the measurements obtained using the TDR one-step method to those obtained form other methods. Conducting su ch side-by-side tests is a critical step in the progress and eventual widespread us age of the one-step method. In addition, all the results are compared against an indepe ndent measurement of the in-place density from a slurry-replacement method. The objective of the independent measurement is to provide a baseline for accurate and unbiased evaluation of TDR a nd other technologies.

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1 CHAPTER 1 – INTRODUCTION Background Quality control of compacted fills and roadway embankments remains a challenging problem. Although the most accura te measurement method for water content remains the ASTM oven-drying procedure, the procedure requir es 24 hours of ovendrying before the results are available. Nuclear density and moisture gages require special certification, due to th e potential haza rds associated with the use of a radioactive material. As such, the University of Sout h Florida has undertaken a research study over the past two years to evaluate the TDR method as an alternative for in-situ density and moisture measurement. The study was part of a nationwide Beta Testing program initiated by the Indiana DOT and Purdue Univer sity. As a result of these efforts, the method has been standardized in 2002 by ASTM under Designation D 6780. While the newly-introduced ASTM Standard Method calls for a two-step process that requires excavation and re -compaction of the field so il, a new one-step method was developed concurrently by Purdue University researchers and represents a breakthrough since no excavation is needed. The procedur e requires the calibration of two soils constants, f and g to relate the dielectric constant to the bulk electrical conductivity of the soil. The field process can be complete d in less than 5 minutes, which provides a significant advantage over the existing procedure. The two soil constants, f and g are dependent on soil type, pore fluid conductivity, and water content. To this end, only a limited number of calibrations have been undert aken as part of the current research project as it is beyond the sc ope of work. Determining these new soil constants for typical highway construction soils in Florida is a crucial step in the progress and eventual widespread usage of the one-step method. Another problem that is the current lack of any methods to evaluate the accuracy of the density measured using TDR a nd other quality control methods. TDR

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2 measurements cannot be evaluated against sa nd cone, nuclear gage, or speedy moisture since the accuracy of these methods remains, in itself, in question. While oven dry measurements are broadly accepted as the “standard” for water content, no such method is available for in-place density. In order to compare the methods to a baseline, it is necessary to accurately determine the moisture content and in-place density of the tested material. Sand cone measurements are highly sensitive to densification of the standard sand. Nuclear density gages that rely on back scatter to measure moisture content are representative of the water content within onl y the top few inches of soil. The use of a reliable method for in-place density measur ement is, therefore, a crucial step in evaluating the accuracy of the TDR method. Organization of Thesis The basic concept of time domain reflect ometry its evolution as well as its relevance to the geotechnical e ngineering field is presented in Chapter 2. Also included in the chapter is a review of the theoretical concepts associated with the One-Step TDR Method. Chapter 3 presents a discussion about the equipment and procedure used for the One-Step TDR Method. Both the calibration and field testing procedure are cover in detail. The calibration constants used in conjunction with the One-Step TDR Method is discussed and presented in Chapter 4. The experimental results from a study to determine the typical range of TDR consta nts for Florida sands are included in the chapter. Also presented are the results from a parametric study on calibration factors. Chapter 5 includes results obtained from a te sting program carried out to evaluate the accuracy of the One-Step TDR Method. Incl uded within the chap ter are comparative results with traditional geotechnical testing methods. Chapter 6 discusses the results obtained from a series of tests that were ca rried out in an effort to establish a new, baseline method for determining in-situ dry density. Detailed ca libration and testing procedures are also outlined within the chap ter. The conclusions of this research and recommendations for further study in this area are presented in Chapter 7.

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3 CHAPTER 2 – LTERATURE REVIEW Evolution of Time Domain Reflectometry Time Domain Reflectometry, or TDR, is an electromagnetic measurement technique that has been used for many years to determine the spatial location and nature of various objects. It was developed in the 1930s by the power and telecommunication industries to locate break s in coaxial cables (Lin et al., 2000). TDR has been compared to wire radar and to this end, TDR devices ar e sometimes referred to as cable radar. The TDR idea was further developed by Fellne r-Feldegg (1969) where the technology was used for measuring permittivity of liquids. Research conducted by Topp et al. (1980) represented a breakthrough fo r TDR by demonstrated a uniq ue relationship between the apparent dielectric constant and the volumetric water content within the soil. Other researchers studied the TDR application by developing a measurement system in which TDR signals are transmitted into a soil medium by the use of metallic rods. Several projects were carried out to evaluate di fferent TDR transmission line configurations (Ledieu et al., 1986; Topp et al., 1982; a nd Dasberg and Dalton, 1985). Although results from these tests indicated a reliable relations hip between the dielectr ic constant to water content, the need for a reliable and routine fiel d technique was still evident. Zeglin et al. (1989) studied several coaxial probe configur ations and found that three and four wire configurations were superior to a two wire system. Studies investigating cable length, quality and type of probe and cable dimensi ons were carried out by Heimovaara (1993) to determine their influence on the accuracy of TDR measurements. Improvements in calibration were made by Dirksen and Da sberg (1993), which accounted for certain differences in mineralogy. Dasberg and Dalton (1985) expanded on the use of TDR by introducing the bulk electrical conductivity as a means of me asuring soil salinity and soil pore-fluid conductivity. Thes e pioneering efforts in TD R technology discussed above proved to be very promising for use in geotechnical applications.

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4 Basic Principles of Time Domain Reflectometry The TDR works on the same principle as radar in that a short electromagnetic wave is emitted and then its reflection measure d. Another way to think about this is to imagine a coaxial cable where the far end is cut, broken, or crimped. When an electromagnetic energy pulse is transmitted dow n the cable, the voltage at the starting point jumps up to a given value instantly and the pulse begins propagating down the cable towards the damaged section. When th e pulse reaches the de fective location an opposing pulse reflects back from the defect towards the initial st arting point. This opposing pulse is created by a change in cable geometry and/or the medium between the outer and inner conductors of th e coaxial line. Once the oppos ing reflection returns to the staring point the voltage abruptly changes, signaling that there is a break at the end of the cable. The TDR measures the time it takes fo r the signal to travel down the cable and reflect back. This travel time depends on the dielectric properties of the insulating material between the center wire and the shie ld in the coaxial cable. Once the time is known it is converted to distance and displayed in the form of a wave. The same concept is used for geotechnical application in that the TDR signal is transmitted down a coaxial cable. The only difference being that the objective is not to find a break in the line as described earlier but to extract soil propertie s. This is accomplished by treating the soil as the insulating material in a coaxial c onfiguration with a cen tral probe and three peripheral probes acting as the central rod and shield respectivel y (Figure 2-1). Development of the ASTM TDR Measurement System As was mentioned previously the us e of TDR technology was fueled by the discovery of a universal calibration equation relating soil volumetric water content to a soil apparent dielectric constant (Topp et al. 1980). Since a ll of the earlier uses of TDR technology were directed at obtaining soil volumetric wa ter content the calibration equation better served the fields of agricultural science and wa ter resources. In an effort to extend TDR technology for use in geotech nical applications Si ddiqui and Drnevich (1995) refined the Topp’s Equation such that gravimetric water content is utilized along with soil dry density. This new approach le d to the development of procedures using

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5 TDR for geotechnical compacti on control (Yu and Drnevich 2004). The procedures developed by Drnevich et al. (2000) called for a two-step fiel d test in which one test is taken with a probe consisting of four coaxial co nfigured spikes driven into the soil and a second test conducted in a compaction mold. Re searches were carried out to evaluate the method’s accuracy and indicated promising re sults for geotechnical applications (Lin, 2000; Siddiqui et al., 2000; Drne vich et al., 2002; Sallam et al., 2004). As a result the method was accepted in the form of ASTM standard D 6780 in 2002. The two-step method discussed above was f ound to be limited in that it only made use of the soil apparent dielectric constant not to mention that the method was also destructive and time consuming. In an effort to streamline the two-step method, Yu and Drnevich (2004) proposed the use of a bul k electrical conductivity measurement to improve the accuracy of the two-step method as well as to eliminate the need to perform a second test in a compaction mold. This im proved method is referred to as the One-Step TDR Method. Figure 2-1. Purdue TDR Measurement Sy stem. Source: Yu and Drnevich (2004).

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6 Basic Principle of the One-Step TDR Method The One-Step TDR Method (Yu and Dr nevich, 2004) makes use of both the apparent dielectric constant a nd the bulk electrical conductivity to estimate two important compaction parameters, soil water content and dry density. The method itself relies on the six soil specific calibration factors that are determined from TDR tests on the same soil through laboratory compaction te sts. An adjusted electrical conductivity is obtained for estimating the water cont ent and dry density in the field through an empirical relationship between the apparent dielectric c onstant and the bulk elec trical conductivity. Determining the Apparent Dielectric Constant, Ka As mention previously, TDR testing syst ems were originally developed to find discontinuities in transmission lines by sending an electromagnetic wave through the cable. The velocity, v at which the wave travels down the cable is given by: aK c v (2-1) Where c is the velocity of an electro magnetic wave in free space (2.998108 m/s). The travel time, t is related to the propagation velocity and the cable length, L by the following: v L t 2 (2-2) Combining Eqn. (2-1) and Eqn. (2-2) a nd solving for the apparent dielectric constant, Ka, the following expression is obtained: 22 L ct Ka (2-3)

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7 The term 2 ct has units of length and is defined as a scaled horizontal distance between the two reflection point s (Figure 2-2) (Baker and Al lmaras, 1990). Thus Eqn. (2-3) can be reduced to a simplified form as: 2 p a aL L K (2-4) Where La is the apparent length and Lp is the length of the soil probe (Yu and Drnevich, 2004). Topp et al. (1980) and other early research ers determined travel times in TDR probes by fitting tangent lines to wave form featur es by hand, either reading directly off the instrument screen or worki ng with photographs of the screen. Since then, automatic wave form acquisition systems have been created that al low the collection of thousands of wave forms (Baker and Allmaras, 1990; Heimovaara and Bouten, 1990; Herklerath et al., 1991), thus necessitati ng the creation of computer programs for automatic interpretation of the wave form to find travel times. Researchers at Purdue University employed an algorithm deve loped by Drnevich and Yu (2001). Figure 2-2. Typical TDR Wave Reflecti on. Source: Drnevi ch et al. (2003).

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8Determining the Bulk Electric Conductivity, ECb The electrical conductivity is another import quantity th at can be obtained from TDR waveforms. Electrical conductivity is a m easure of a material's ability to conduct an electric current. Basically, electrical conductivity is the reciprocal of the electrical resistance. As the TDR wave propagates through the soil probe s the signal is attenuated in proportion to the electrical conductivity along the travel path. Based on dissipation analysis Dalton et al. (1984) proposed the simultaneous measurement of the apparent dielectric constant and bulk electrical conductivity. Yu and Drnevich (2004) further developed the idea and proposed the following expression: 1 1f s bV V C EC (2-5) Where Vs is the source voltage and equal to twice the step voltage, Vf is the long term voltage level (Figure 2-3), and C is a constant related to the probe configuration given by: i o s pd d R L C ln 2 (2-6) Where Lp is the length of the probe, Rs is the internal resistance of the pulse generator, do and di are the outer and inne r conductor diameters, respectively (Giese and Tiemann, 1975).

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9 Calibration Relationship for Soil Apparent Dielectric Constant Topp et al. (1980) showed that for soils w ith a wide range of mineral content, a single equation was applicable. Their equation is now widely used for calibration and is referred to as Topp’s equation. 2 2 2 4 3 610 3 5 10 92 2 10 5 5 10 3 4 x K x K x K xa a a (2-7) Where the volumetric water content, is defined as: solids waterV V (2-8) Topp’s equation has been studied by nume rous authors on several soils and is currently the most widely used calibration eq uation for TDR applications. Several other researchers (Ledieu et al., 1986; Alharthi and Lange, 1987) assumed a linear relationship Figure 2-3. Electrical Conductivity Wave Analysis. Yu and Drnevich (2004). Scaled Distance (m) Relative Volta g e ( V )

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10 between the square root of the apparent di electric constant and the volumetric water content, : aKba (2-9) Where a and b are calibration constants: a = 1.545 and b = 8.787 in Ledieu et al. (1986); a =1.59 and b = 7.83 in Alharthi and La nge (1987). Malicki et al. (1996) developed a calibra tion equation which incorporat ed the effects of density given by: b b b aK 18.117.7 159.0618.0819.02 50 (2-10) Where b is measured in units of grams/cm3. Yu and Drnevich (2004) argued that these calibration equations are difficult to a pply for geotechnical a pplications. As a result, Siddiqui and Drnevich (1995) developed the following expression: bwaKd w a (2-11) Where a and b are soil specific calibration constants, d is the dry density of the soil, w is the density of water, and w is the gravimetric water content. An in-depth discussion of this equation and its co nstants are addressed in Chapter 4. Calibration Relationship for Bulk Soil Electrical Conductivity In an effort to relate the bulk soil electr ical conductivity to soil physical properties Rhoades et al. (1976) proposed the following equation which relates the bulk electrical conductivity, ECb, to pore fluid conductivity, ECw. s w bECECTEC (2-12)

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11 Where ECs is the soil surface conductance and T is a geometric factor given by: ' a b T (2-13) Where a' and b' are soil specific constants and is the volumetric water content. The bulk electrical conductiv ity of soil can then be expressed as a second order polynomial of volumetric water content by: s w w bEC EC b EC a EC '2 (2-14) Again, Yu and Drnevich (2004) argue that the equation is inadequate for geotechnical engineering applications. As a result, they proposed a relationship very similar to the Siddiqui and Dr nevich equation for apparent dielectric constant and gravimetric water content (Yu and Drnevich 2004). The expression can be given as follows: dw c ECd w b (2-15) Where “ c ” and “ d ” are soil specific calibration constants, d is the dry density of the soil, w is the density of water, and w is the gravimetric water content. Further discussion on this equation will be addressed in Chapter 4. Dielectric Constant Bulk Elec trical Conductivity Relationship For all practical purposes the apparent dielectric constant and bulk electrical conductivity are viewed as inde pendent measurements obtained from the TDR waveform. However, Malicki et al. (1994) and Hilhorst (2000) found th at a good linear relationship existed between the apparent dielectric consta nt and bulk soil electr ical conductivity. Yu and Drnevich (2004) also suggest that the apparent dielectric constant ( Ka) and bulk electrical conductivity ( ECb) are related since Eqns. (211) and (2-15) are both are

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12 functions of water content and dry density of the soil. Thus, they proposed a third and final calibration equation given by: a bK g f EC (2-16) Where “ f ” and “ g ” are soil specific calibration constants. The significance of Eqn. (2-16) as well as the calibration of “ f ” and “ g ” is covered in detail in Chapter 4. Data Reduction Process to Obtain Water Content and Dry Density After the TDR calibration constants are determined for a particular soil the dry density and the water content can be comput ed in the field by simultaneously solving Eqns. (2-11) and (2-15). The dielectric constant, Ka, and the bulk elec trical conductivity, ECb, are measured and the following equations ca n be used to determine field dry density and water content: cb ad EC b K db a d (2-17) a b b aK d EC b EC a K c w (2-18) However, due to the dominance of por e fluid conductivity on Eqn. (2-15), satisfactory results are typically not obtain ed (Yu and Drnevich, 2004). Many factors can contribute to this inaccuracy, including random e rrors in dielectric c onstant and electrical conductivity measurements. The primary source of error is due to differences in pore fluid conductivity between calib ration samples and field a nd as a result, accurate measurements are not obtained. In an effort to compensate for the measurement inaccuracies Yu and Drnevich (2004) proposed an adjustment procedure depi cted graphically in Figure 2-4. Their

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13 approach was to “adjust” the field situation so that the laborator y calibrations can be applied to it. The reasoni ng behind this methodology was ba se on the impracticality of determining calibration values of “c” and “d” for every conductiv ity likely to be encountered in the field. The water content and dry density of the fi eld sample can then be calculated using Eqns. (2-17) and (2-18) with the adjusted values of Ka, adj and ECb, adj. field a adj aK K, (2-19) 2 field a bK g f EC (2-20) Figure 2-4. Adjusting th e Field Sample to the La boratory Calibration. Source: Yu and Drnevich (2004).

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14 CHAPTER 3 – TDR EQUIPMENT AND PROCEDURE Introduction The factors which influence the wave tr ansmission were studied by Siddiqui and Drnevich (1995) and as a result, transmissi on line components were designed and built. The TDR components were designe d to be robust, easy to use, and provide superior wave transmission for field measurement of the soil apparent dielectric constant and bulk electrical conductivity TDR Measurement System The system configuration of the basi c TDR measurement device is shown in Figure 3-1. The soil probe measurement system is basically made up of three essential components: (1) coaxial cable, (2) coaxial head, a nd (3) either a coax ial cylinder (used for calibration purposes) or multiple rod probe (used for field measurement). The coaxial cable consists of a center conducting wi re surrounded by a cylinder casing, which acts as the outer conductor (Lin et al., 2000). Figure 3-2 shows the main components of the coaxial head (CH). The CH serves as a transition between the actual Figure 3-1. TDR System Configuration. Sour ce: Lin et al. (2000).

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15 coaxial cable and coaxial cylinder (CC) or mu ltiple rod probe (MRP). The coaxial head (CH) has one center stud and three perimete r studs. The center stud and two of the perimeter studs have fixed lengths of 21mm. The third perimeter st ud is spring loaded to ensure full contact with the four field pr obes or the ring and ce nter probe in mold. The coaxial cylinder (CC) transmission line consists generally of a CC mold, a CC ring, and a central rod. The CC mold is basically a modified compaction mold with an inner diameter of 101.6 mm and a height of 232.87 mm The CC ring rest on top of the mold and is held in place by an offset gr ove. The ring serves as an extension collar during the compaction stage a nd as a part of the coaxia l cylinder (CC) during the measurement stage. The central rod is made of stainless steel a nd has a length of 234 mm and a diameter of 8 mm. A plas tic centering jig is used to guide the central rod during the driving stage. Figure 3-3 shows th e coaxial cylinder configuration. The multiple rod probe (MRP) consists of one central rod and three perimeter rods (9.5 mm diameter and a length of 236 mm ), which are driven into the soil. The proper rod configuration is achieved by using a temporary detachable template. The template ensures that the coaxial head pins line-up perfectly with each of the multiple rod Figure 3-2. Configuration of Coax ial Head. Source: TDR Manual

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16 probes. After the spikes have been driven, the template is removed and the coaxial head (CH) is placed on top of the spikes (Figure 3-4). This forms a coaxial line in the soil (Drnevich et al., 2001). Figure 3-4. The Multiple Rod Probe (MRP). Source: Siddi q ui and Drnevich ( 1995 ) Figure 3-3. The Coaxial Cyli nder (CC) Transmission Line. Source: Siddiqui a nd Drnevich (1995).

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17Tool Case, Electronics Case, Wiring of the TDR System TDR tool cases are designed to make the system more compact and easy to handle in the field. Several generations of t ool cases have been updated by now. Each generation was significantly improved over previous ones. These improvements have significantly increased efficiency in the field. Purdue University provided the University of South Florida with two cases. One case cont ains the TDR Probes, molds, digital scale, and tools. The other case contains mostly el ectronic components. The apparatus stored in each of the cases are summarized below. Case 1 – TDR Tool Case The TDR tool case is a r ugged field case that is equi pped with two wheels and an extension handle for ease of transport. The case itself houses all the basic TDR equipment, accessories and tools for pe rforming the test (Figure 3-5). Case 2 – TDR100 Sample, Battery, Charger, and Laptop The second case (Figure 3-6 and 3-6) is basically an oversized briefcase that houses the electronics for performing the TDR measurements, ma king the calculations, and storing the data. A laptop computer is connected to SP232 serial communication module to retrieve data obtained from th e Campbell Scientific TDR100 Time Domain Figure 3-5. TDR Tool Case. Source: Drnevich et al. (2003).

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18 Reflectometer. The TDR100 Time-Domain Refl ectometer is the core of the Campbell Scientific Time Domain Reflectometry system It generates a very short rise time electro-magnetic pulse that is applied to a co axial system which includes a TDR probe for soil water and density measurements and samp les and digitizes the resulting reflection waveform for analysis or storage. Figure 3-7. Layout of the TDR Elect ronics Case. Source: TDR Manual. Figure 3-6. TDR Electronics Case.

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19TDR Software (PMTDR-SM) The Purdue Method TDR Simplified Method (PMTDR-SM) is the software used for automation of soil water c ontent and dry density using the One-Step TDR Method. PMTDR-SM Version 1.2.2 was the most curre nt version available at the time this research was conducted. The software is co ntinuously being updated to provide a more user friendly interface. The TDR software performs the following functions: 1) Operates the TDR100 to obtai n an appropriate waveform. 2) Display the TDR wave graphi cal on the computer screen. 3) Analysis the wave form to obtain the a pparent dielectric c onstant and the bulk electrical conductivity of the soil. 4) Computes the soil water c ontent and dry density. 5) Logs information related to th e test and saves the results. 6) Provides a module to facilita te the calibration process. The software consists of two input screens. The first screen is the In-Situ MRP Test which prompts the user to input project name, contract No., ope rator, test location, test number, temperature, and type of soil (cohe sive or cohesionless) (Figure 3-8). Other input parameters include the MRP probe c onfiguration measurements and the soil specific constants for the soil being tested.

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20 The second screen is used for the CC Mold Test in which the user is prompted to input the same parameters mentioned for the In-situ MRP test as well as the mass of empty mold, mass of mold, wet soil and the volume of mold and the mold probe dimensions (Figure 3-9). Figure 3-8. In-situ MRP Input Screen. Source: PMTDR-SM.

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21 Testing Procedure The One-Step TDR Method for soil water content and dry dens ity determination requires both laboratory calibrati on and field testing procedures. Before either of two testing procedure can be perfor med, the apparatus itself must be calibrated. The next few sections outline the required steps fo r performing a complete TDR test. Apparatus Calibration Before the lab and in-situ test can be c onducted a calibration of the test equipment must be completed. This involves determining the following four items: Figure 3-9. CC Mold Test Input Screen. Source: PMTDR-SM.

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22 1) Determine the average length of the spikes for the in-place test. This is done by inserting each spike into the MRP guide template and measuring the length that each spike protrudes from the template when fully inserted. All measured lengths should be equal to the aver age length within 0.5 mm. A typical field probe length should be approximately 0.2 m. 2) Determine the volume of the cylindrical mold (CC). The mold provided with the equipment here at the University of South Florida is twice the he ight of a standard compaction mold and has a volume of 1888 cm3. 3) Determine the mass of the empty cylindrical mold (CC) including the plastic base-plate, but without the ring collar. A typical valu e for the mass of the clean and empty cylindrical mold is approximately 4,380 g. 4) Determine the length of the central rod fo r insertion into the compaction mold. A typical value for the mold probe length is approximately 0.25 m. Laboratory Test The purpose of the laboratory test is to obtain soil-specific parameters (a, b, c, d, f, and g). The determination require s that 5 test at different water contents be performed using the cylindrical mold probe. Calibrati on can be conducted in conjunction with a set of standard compaction test (ASTM D 698 and ASTM D1557) provided that a nonconductive base is used with the standard four inch stai nless steel compaction mold. In order to properly calibrate the soil the ambi ent temperature and th e temperature of the soil should be within 15 to 25 degrees Celsius. The Procedure for determining soil specifi c constants is outlined as follows: 1) Obtain a representative soil sample from the borrow pit or from the testing site. The sample should be large enough for at least five compacted samples. 2) Air-dry the soil sample and pass the mate rial through a No. 4 (4.75 mm) sieve. 3) Prepare five samples that have varying wa ter contents within the range of that expected in the field. Typical field moistures rang e between 10-15%. For best results vary the water conten t between each sample by 2-3%.

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23 4) Assemble and secure the cylindrical mold ring collar and base plate 5) Place the soil into the cylindrical mold and compact in six uniform lifts applying 10 blows per lift using the aluminum tamping rod (Figure 3-10). 6) Remove the ring collar and strike the surf ace level with a straight edge. Remove any soil that may be resting on the base plate with a brush. 7) Weigh and record the mass of the mold and the wet soil to the nearest gram. 8) Place the guide template for the center r od on the mold. Drive the central rod through the guide hole and into the soil until the top of the rod is flush with the surface of the template (Figure 3-11). Figure 3-11. Central Spike Driven Th rough the Guide and into the Sample. Figure 3-10. Compacting the Cylindrical Mold.

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24 9) Carefully remove the guide template from the cylindrical mold ensuring that the central rod remains in place and undisturbed. 10) Place the ring collar back onto the cylindric al mold and ensure that the electrical contact surfaces are clean. 11) Set the coaxial head (CH) on the ring colla r such that the central stud is in-line with the central rod and the three outer studs are contacti ng the ring collar. Rotating and/or sliding the CH to f acilitate good contact is advisable. 12) Make a TDR reading using the TDR measur ement system and software to obtain the apparent dielectric constant (Ka) and the bulk electr ical conductivity (ECb) (Figure 3-12). 13) Remove the soil form the mold. Secure a portion of the sample (ideally from the center of the sample) for water content determination. Obtain the water content per ASTM D2216. 14) Repeat steps 5 through 13 for each of the remaining soil specimens. Figure 3-12. Taking the TDR Measurement.

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25 The above procedure will provide four quantitative entities for each successive iteration: (1) water content, (2) dry dens ity by knowing the volum e and weight of the mold, (3) apparent dielectric constant, a nd (4) bulk electrical conductivity. Knowing these four entities enables the user to ca librate the soil through a series of linear regression plots. Soil constants “a” and “b” are found by plotting the squa re root of the apparent dielectric constant multiplied by the ratio of the density of wa ter to the dry density of the soil versus the oven dry water content. A best fit linear regression line is then fitted to the data where “a” is the y-intercept and “b” is the slope of the lin e. Figure 3-13 shows an example calculation of “a” and “b”. Soil constants “c” and “d” are found by plotting the s quare root of the bulk electrical conductivity multiplied by the ratio of the density of water to the dry density of the soil versus the oven dry wate r content. A best fit linear regression line is then fitted to the data where “c” is the y-intercept and “d” is the slope of the line. Figure 3-14 shows an example calculation of “c” and “d”. Figure 3-13. Example Calibration for “a” and “b”. y = 8.3573x + 0.9772 R2 = 0.9929 0 0.5 1 1.5 2 2.5 00.020.040.060.080.10.120.14 Water Content (%) Ka w/ w

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26 Soil constants “f” and “g” are found by plotting the s quare root of the bulk electrical conductivity versus the square root of the appa rent dielectric constant. A best fit linear regression line is then fitted to the data where “f” is the y-intercept and “g” is the slope of the line. Figure 3-15 shows an example calculation of “f” and “g”. In-situ Test The field testing procedure and test appa ratus for the One-Step Method are similar to those specified by ASTM D6780 for the Tw o-Step Method. The only difference being the omission of the steps for removing the soil, compacting the soil in the mold, and Figure 3-15. Example Calibration for “f” and “g”. y = 0.0315x 0.0258 R2 = 0.9907 0 0.02 0.04 0.06 0.08 0.1 1.7522.252.52.7533.253.53.75 Ka EC b Figure 3-14. Example Calibration for “c” and “d”. y = 0.2753x + 0.0145 R2 = 0.9909 0 0.01 0.02 0.03 0.04 0.05 0.06 00.020.040.060.080.10.120.14 Water Content (%) ECb w/ d

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27 running a second TDR test on the soil in the mold. Eliminati ng these steps results in a significant reduction in the time require d to perform the field test. The procedure for conducting the fiel d test is summarized as follows: 1) Prepare the soil surface by leveling the ar ea (typically 300 mm by 300 mm) to be tested. Removal of the top inch of so il is recommended provided that the soil surface is wet form a recent rain or is dried out from extreme exposure. The leveled surface should be free of voids. If voids exist, they should be filled and smoothed accordingly. 2) Place the spike driving template such th at it is centered on the prepared soil surface. The template should be in the cl osed position with the retaining pin fully seated. Check to ensure that the template is in full contact with soil surface. If any gaps are present between the template and the soil, remove the template and further smooth the surface. 3) Use the brass hammer to drive the thr ee outer spikes through the holes in the template and into the soil (Figure 3-16). Once the outer three spikes are driven, drive the fourth and final central spike. Ch eck to ensure that a ll of the spike heads are fully seat and touching the template surface. If large particles within the soil matrix cause the spike to deviate from th e vertical position, remove all the spikes and select a new test location. Figure 3-16. Driving Spikes th rough Template into Soil. Source: TDR Manual.

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28 4) Remove the retaining pin from the driving template. Pry the template open to expose all four TDR spike heads (Figure 3-17). Opening the template must be done carefully to ensure that the spikes are not disturbe d. This step is crucial because air gaps between the field probe s and the surrounding soil affect the TDR signal. 5) Place the coaxial head on top of the spikes such that each stud is centered on its respective field probe (Figur e 3-18). Slide and/or rotate the coaxial head to facilitate good contact with the probes. Figure 3-18. Placement of Coaxial Head (CH) on Spikes. Source: TDR Manual. Figure 3-17. Removal of the Template. Source: TDR Manual.

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29 6) Connect the CS TDR100 to the coaxial head using the coaxial cable provided with the equipment. Ensure all cable connector are clean and free of dust. 7) Take a TDR reading using the TDR measur ement system and software to obtain water content and dry density. The field testing procedure outlined above can be completed in 3-5 minutes by an experienced technician. It s hould noted that the water conten t and dry density obtained in step seven are not valid until the laboratory test data and soil specific constants are determined and entered into the a ppropriate TDR program fields.

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30 CHAPTER 4 – EVALUATION OF TDR CONSTANTS Introduction In order to determine water content and dry density of compacted fills using the One-Step TDR Method, a series of soil spec ific calibration constants must be obtained prior to field testing. There are a total of six soil specific constant (a, b, c, d, f, and g) that need to be found. Soil constants “a” and “b” are parameters that relate the gravimetric moisture content to the so il dielectric constant. Constants “c” and “d” relate the gravimetric moisture conten t to the bulk electrical conducti vity of the soil. Finally, constants “f” and “g” relate the dielectric constant to the bulk electri cal conductivity. These soil constants may vary widely de pending on soil composition and site specific conditions. This chapter presents experiment al results from a study to determine the typical range of TDR constant s for Florida sands by performi ng a series of TDR tests in the calibration mold for several soils obtaine d at local constructi on projects between Tampa and Orlando. Also presented are th e results from a parametric study on the calibration constants. Calibration Constants “ a ” and “ b ” A study by Siddiqui and Drnevi ch (1995) and Siddiqui et al (2000) utilized a relationship (Eqn. 4-1) betw een gravimetric water content and soil dry densities to determine soil constants “a” and “b.” bw a Kd w a (4-1) Where Ka is the apparent dielectric constant, w is the density of water, d is the dry density of the soil, and w is the gravimetric water content.

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31 The process for obtaining th e TDR calibration constants “a” and “b” was discussed in detail in Chapter 3. By substituting the volumetric water content, (Eqn. 42) into Equation (4-1), the calibration equati on can be converted into one for volumetric water content as given in Equation (4-3). w dw (4-2) b a Kw d a (4-3) When the volumetric water content ( ) is zero Eqn. (4-3) reduces to: d w s aK a (4-4) Where Ka,s is the apparent dielectric constant of the dry soil. Soil constant “a” is thus termed the refraction i ndex of the soil solids that is normalized by the soil dry density. Typical values of “a” range from 0.7 to 1.85 (Yu and Drnevich, 2004). When the volumetric water content ( ) is 100 percent Eqn. (4-3) reduces to: w aK b, (4-5) Soil constant “b” is defined as the refr action index of the pore fluid. Typical values of Ka,w measured by TDR are close to 81 at 20C. This yields a “b” value of about 9 (Yu and Drnevich, 2004).

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32Calibration Constants “ c ” and “ d ” Yu and Drnevich (2004) argue that the el ectrical conductivity from the pore fluid is typically the dominating factor in the de termination of the bulk electrical conductivity of soil. As a result, the amount of pore fl uid present in the soil generally dominates the bulk electrical conductivity of the soil. This phenomenon is also noted in the measurement of the apparent dielectric cons tant (Sihovola, 1999). Using this analogy, Yu and Drnevich (2004) proposed a calib ration relationship for bulk electrical conductivity similar to the Si ddiqui and Drnevich (1995) re lationship for soil apparent dielectric constant. The proposed calibr ation relationship can be expressed as: dw c ECd w b (4-6) where ECb is the bulk electrical conductivity. Equa tion (4-6) is used in conjunction with the procedure outlined in Chapter 3 to determine constants “c” and “d.” If Equation (4-6) is expressed in terms of volumetric water c ontent the following expr ession is obtained: d c ECw d b (4-7) When the volumetric water content is zero: s d wEC c (4-8) The calibration constant “c” is related to surface conduc tance of the soil particles normalized by dry density (Yu and Drnevich, 2004). When the volumetric water content is 100 percent: bEC d (4-9)

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33 The calibration constant “d” accounts for the effect of soil type and pore fluid properties (Yu and Drnevich, 2004). Calibration Constants “ f ” and “ g ” The apparent dielectric c onstant and bulk electrical conductivity are typically viewed as independent measurements obt ained from the TDR waveform; however several studies (Malicki et al., 1994, Hilhorst, 2000, White et al., 1994) have shown that good linear relationships exist between the a pparent dielectric c onstant and bulk soil electrical conductivity. Yu and Drnevich ( 2004) point out that the two independent equations (4-1) and (4-6) are both functions of water content and dry density of the soil. As a result, Yu and Drnevich (2004) suggest that the apparent dielectric constant (Ka) and bulk electrical conductivity (ECb) must be related to one another. By combining Equations (4-1) and (4-6) the followi ng expression can be obtained: a w d bK b d b d a c b EC (4-10) The soil calibration factor “g” is related only to the slopes of the calibration curves for apparent dielectric constant and for electrical conductivity and is given by: b d g (4-11) The soil calibration factor “f” is related to all four cal ibration constants as well as the soil dry density and is given by: w db ad bc f (4-12)

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34 If Equation (4-10) is expressed in te rms of Equation (4-11) and (4-12) the following expression is obtained: a bK g f EC (4-13) Calibration Testing Program In an effort to determine the typical ra nge of TDR soil constants for Florida sands an experimental program was employed where a series of TDR tests were run in the calibration mold. Basically soils were collect from several locations within the state and brought back to the university soils lab. Once the soils were secured in the lab they were dried and classified in accordance with ASTM 422 and ASTM D2487. After classifying the soil, TDR calibration procedures were performed in accordance with ASTM D6780. The ultimate goal of this testing program was to find standard calibration constant based on soil type, project location, or possible the combination of both. Calibration Test Results In total, some 40 soils were classified and calibrated. This yielded nearly 250 individual calibration points. Table 4-1 provides a summary of the result obtained form the testing program. Figure 4-1, 4-2, a nd 4-3 depict the result graphically. Results and Discussion for “a” and “b” The Siddiqui and Drnevich (1995) relati onship was used to determine the soil constants “a” and “b”. The process relied on performi ng the TDR method on a particular soil in the mold at different moisture contents. In this case the soil dielectric constant in the mold Ka is measured as an output from the TDR software. The wet density is readily measured since the mold’s volume and weight are both known quantities. The moisture content can be determined by the oven-dry method, AS TM D2216. The two unknowns in this equation (Eqn. 4-1) ar e, therefore, the constants “a” and “b”. If the left hand side of the equation is plotted against the moisture content, the results co uld be regressed to a

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35 straight line with a slope equal to the constant “b” and an intercept equal to the constant “a”. The results of all tests are plotted on a single graph (Figure 4-1). Values of 0.98 and 8.55 were determined for constants “a” and “b” respectively. The correlation factor, or R-value, for the trend line used for all the data was 0.973, i ndicative of a strong correlation. Table 4-1. TDR Soil Cons tants for Florida Sands.

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36 Sallam et al. (2004) determined the calibration parameters “a” and “b” encountered in common soils in the state of Florida. A final recommendation of “a” = 1 and “b” = 8.5 was made. Soils tested in the study echo their results. Results and Discussion for “c” and “d” The Yu and Drnevich (2004) relationship was used to determin e the soil constants “c” and “d”. Again, the process relied on pe rforming the TDR method on a particular soil in the mold at different moisture c ontents. In this case the bulk electrical conductivity in the mold ECb is measured as an output from the TDR software. Just as before, by knowing the volume and weight of th e mold in conjunction with the moisture content the dry density was determined. Th e two unknowns in this equation (Eqn. 4-6) are, therefore, the constants “c” and “d”. If the left hand side of the equation is plotted against the moisture content, the results could be regressed to a strai ght line with a slope equal to the constant “d” and an intercept equal to the constant “c”. The results of all tests are plotted on a single gr aph (Figure 4-2). The results show a definite distinction Figure 4-1. Individual Calib ration Points for Obtaining “a” and “b”. y = 8.554x + 0.977 R2 = 0.973 0.5 1 1.5 2 2.5 3 0.0%5.0%10.0%15.0%20.0%25.0% Water Content (%)sqrt(Ka)*rw/r d Soil Type A-1-b Soil Type A-3 Soil Type A-2-4

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37 between the soil types A-1-b and A-2-4. The delineation between the two soil types is represented by the solid black line. The slopes or “d” values of the A-1-b soils are all below the delineation line. Th e slopes for the A-2-4 soils are all above the delineation line. This is predominantly due to the dependence of “d” on the pore fluid conductivity of the soil being tested. Finer grained sa nds (A-2-4) are more conductive than coarser sands (A-1-b). The more conductive the soil the higher the measured value of the bulk electrical conductivity thus the higher the valu e of the soil constant “d” and vise versa. Values for “d” obtained from this study ranged from 0.146 to 0.632 for A-1-b soils, from 0.235 to 0.801 for A-3 soils, and from 0.269 to 0.466 for A-2-4 soils. The result from this study also showed that the values of “c” ranged between 0.0036 and 0.0593 for Florida sands. However it appears that calibration constant “c” may have a unique value at zero water conten t. In an effort to study this observation several soils were dried and test at zero water content. Table 4-2 summarizes the findings. Figure 4-2. Individual Calib ration Points for Obtaining “c” and “d”. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.0%5.0%10.0%15.0%20.0%25.0% Water Content (%)sqrt(ECb)*rw/r d Soil Type A-1-b Soil Type A-3 Soil Type A-2-4

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38 The results presented in Table 4-2 show that the variation in soil constant “c” is quite small with a standard deviation of 0.002. The average value of 0.01 is recommended in the absences of a soil specific constant for “c”. Results and Discussion for “f” and “g” The values for both “f” and “g” are dependent on the values of “a”, “b”, “c”, and “d” (see Eqns 4-11 and 412). Soil constant “g” varies systematically with pore fluid conductivity as does constant “d”. This was expected as “g” is a function of “d” and “b”. Since “b” is largely unaffected by pore flui d conductivity, the variation of “g” is attributed to changes in “d.” As was the case for “d” there appears to be a demarcation between the finer sands and the coarser sa nds. For Florida sands, values of “f” range from -0.0923 to 0.0285, and values of “g” ranged from 0.021 to 0.0836. Table 4-2. Calibration of TDR Soil Constant “c”.

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39 Parametric Study on So il Calibration Constants The overall objective of this calibration study was to provide guidance for proper selection of TDR soil calibration constants. One aspect of this effort was to perform a parametric study of the calibration factors us ing the TDR software. The testing program discussed above showed that Florida sands have a typical range of values for each of the six constants respectively. In this parametric study, only a single dimension was varied while maintaining the remaining parameters at constant values. Due to the fact that “a” and “c” are fairly well defined for Florida sands, this effort was limited in scope to soil parameter “b” and “d”. Plots showing the influence of parameters on water content and dry density are presented in Figures 4-4 and 4-5. Effects of “b” on Water Content and Dry Density The values of “b” were varied such that they were in the range of typical values found in the previous study discussed above. It can be seen fro m Figure 4-4 that both Figure 4-3. Individual Calib ration Points for Obtaining “f” and “g”. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.51.01.52.02.53.0 sqrt(Ka)*rw/rdsqrt(ECb)*rw/r d Soil Type A-1-b Soil Type A-3 Soil Type A-2-4

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40 the water content and the dry density can vary as much as five percent when the calibration constant “b” is varied by a factor of 0.3. A study done by Sallam et al. (2004) reported similar results. Effects of “d”on Water Content and Dry Density Just as in the case of “b” the values of “d” were varied such that they were in the range of typical values found in the previous study discussed above. It can be seen from Figure 4-5 that the water content is more sensitive to a change in “d” than the dry density. However it should be pointed out that changing the value of “d” by a factor of 0.1 affects the dry density reading by nearly 20%. Th is is a significant fi nding in terms of how calibration factors can affect fi eld readings. More simply put if the calibration constants found in the lab are not in agr eement with what is found in th e field, density readings will be severely altered. Figure 4-4. Parametric Study on Soil Constant “b”. -15.0% -10.0% -5.0% 0.0% 5.0% 10.0% 15.0% 20.0% -1.00-0.80-0.60-0.40-0.200.000.200.400.600.801.00 b% change Wc, %ge Dry Dens., %ge

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41 Summary Investigation into the soil specific TDR calibration constants proved to be valuable. Soil constants “a” and “b” were found to behave cons istently with previous studies. It appears that soil constant “c” is a unique point for a given soil and it may be possible to catalog values based on soil type. Soil constant “d” was demonstrated to change systematically with pore fluid conductiv ity as previous research had indicated. Soil constants “f” and “g” change with the pore fluid c onductivity of the soil since they are calculated from constant “a”, “b”, “c”, and “d”. Constant “g” behaves, in general, similar to constant “d.” It is also noted that for a calibration plot of the dielectric constant and the bulk electri cal conductivity there may exis t a unique point at the dry condition for a particular soil at which true ca libration lines intersect. Also a parametric study on the calibration constants revealed that both the wate r content and the dry density are greatly affect with little va riation of the soil constant “d”. Figure 4-5. Parametric Study on Soil Constant “d”. -50.0% 0.0% 50.0% 100.0% 150.0% 200.0% -0.25-0.2-0.15-0.1-0.0500.050.10.15 d% change Wc, %ge Dry Dens., %ge

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42 CHAPTER 5 – TDR COMPARED TO TRADITIONAL METHODS Introduction The advances in TDR technology that le d to the development of the one-step TDR method have been the focus of previous chapters. Due to the recent nature of these developments a testing program has been implemented to compare the one-step method with traditional methods. In April of 2004, a report on the Two-Step TDR Method was submitted to the state by the University of S outh Florida (Sallam et al., 2004). The report detailed a field study that was carried out in conjunction with the Florida Department of Transportation (FDOT) to evaluate the rela tive accuracy of the ASTM TDR two-step method. The testing program included a series of side by side tests with the TDR twostep method and the nuclear, sand cone and dr ive sleeve methods. In keeping with this testing regime a similar study was conducted to evaluate the One-St ep TDR Method. For purposes of this study, the nuclear method was selected to assess th e accuracy of the TDR one-step method. This method was selected ba sed on its widespread use across the state. The drive sleeve and the sand cone methods disc ussed in chapter two were not considered in this particular study since they do not reflect the st ate of practice. The nuclear method is only used in pract ice for rock base materials, not for embankment or subgrade soils. Because the nu clear moisture measurement uses the back scatter method and has a limited depth of measurement, the speedy moisture method is often used for embankments and subgrades. In the context of the comparative study outlined in this chapter, all three methods speedy, nuclear, and TDR moistures were addressed. The oven dry moisture content wa s taken in order to get the most accurate baseline.

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43Testing Program The widespread use of the nuclear method by engineering practitioners allows for ready access to a large amount of data. Th e nuclear method is commonly implemented at a variety of job sites across the state of Flor ida. TDR measurements can easily be taken simultaneously with routine nuclear gauge te sting using the TDR method. Samples were collected from all testing locations and were taken to the laborator y to obtain a baseline oven dry water content. Due to the lack of a baseline method for measuring in-situ soil dry density, the nuclear moist density was used as a baseline with the dry density backcalculated from the oven dry moisture content. This, of course, is ne ither accurate nor an unbiased measure; however it wa s the method most readily availa ble at the early stages of the research. Test Results A series of side-by-side tests were carried out at several locations throughout Florida using the speedy moisture, nuclea r gauge and the TDR one-step method. Calibration values were determined using the calibration procedures outlined in chapter three. These unique calibration constants were used for field TDR measurements. A summary of test locations and soil types for the nuclear to TDR comparison is displayed in Table 5-1. Testing was carried out at two highway projects. Seve ral tests were run at each location. All samples tested were comm on construction soils encountered in Florida (A-3 sands). Table 5-1. Testing Locations and Information. Location County/City No. of TDR No. of Speedy No. of Nuclear Soil Type(s) I-4 Tampa 3 3 6 A-3 US 301 Hillsborough 10 30 30 A-3 Table 5-2 and 5-3 disp lays the TDR, speedy a nd nuclear water content measurements recorded at each test site al ong with the oven dry baseline water content measured in the laboratory. The percent erro r and absolute error was then calculated by

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44 comparing the field water content measuremen ts to the baseline water content values. The data from Table 5-2 is di splayed graphically in Figures 5-1 and 5-2. Data points for speedy, nuclear and TDR testing was plotted along with a 1:1 line. Table 5-2. Speedy Water Content Comparison Results. Location Test Oven wc TDR wc Speedy wc % Error TDR % Error Speedy Absolute TDR Absolute Speedy I-4 1 5.3 6.5 6.7 23.6% 27.4% 1.24% 1.44% I-4 2 3.8 4.4 4.6 16.4% 21.7% 0.62% 0.82% I-4 3 4.3 5.1 4.9 17.8% 12.0% 0.77% 0.52% US 301 1a 9.3 9.0 7.4 -3.2% -20.4% -0.30% -1.90% US 301 1b 9.2 8.3 -9.8% -0.90% US 301 1c 9.5 8.6 -9.5% -0.90% US 301 2a 6.5 6.8 7.3 4.6% 12.3% 0.30% 0.80% US 301 2b 8.3 6.9 -16.9% -1.40% US 301 2c 6.5 7.6 16.9% 1.10% US 301 3a 4.7 5.8 4.8 23.4% 2.1% 1.10% 0.10% US 301 3b 5.9 5.8 -1.7% -0.10% US 301 3c 7.3 4.6 -37.0% -2.70% US 301 4a 6.4 6.7 6.8 4.7% 6.2% 0.30% 0.40% US 301 4b 5.4 6.5 20.4% 1.10% US 301 4c 5.1 5.8 13.7% 0.70% US 301 5a 8.1 6.7 9.2 -17.3% 13.6% -1.40% 1.10% US 301 5b 5.3 6.0 13.2% 0.70% US 301 5c 6.7 7.3 9.0% 0.60% US 301 6a 6.6 6.9 3.5 4.5% -47.0% 0.30% -3.10% US 301 6b 7.9 8.0 1.3% 0.10% US 301 6c 6.3 6.4 1.6% 0.10% US 301 7a 10.5 9.7 10.1 -7.6% -3.8% -0.80% -0.40% US 301 7b 10.0 5.6 -44.0% -4.40% US 301 7c 8.0 3.6 -55.0% -4.40% US 301 8a 7.6 6.9 7.3 -9.2% -3.9% -0.70% -0.30% US 301 8b 7.2 7.6 5.6% 0.40% US 301 8c 7.2 7.6 5.6% 0.40% US 301 9a 7.6 8.1 8.0 6.6% 5.3% 0.50% 0.40% US 301 9b 7.9 8.3 5.1% 0.40% US 301 9c 8.3 8.5 2.4% 0.20% US 301 10a 8.3 8.0 8.3 -3.6% 0.0% -0.30% 0.00% US 301 10b 9.0 8.1 -10.0% -0.90% US 301 10c 7.5 8.0 6.7% 0.50%

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45 Table 5-3. Nuclear Water Content Comparison Results. Location Test Oven wc TDR wc Nuclear wc % Error TDR % Error Nuclear Absolute TDR Absolute Nuclear I-4 1 5.3 6.5 5.6 23.6% 6.5% 1.24% 0.34% I-4 2 3.8 4.4 4.0 16.4% 5.8% 0.62% 0.22% I-4 3 4.3 5.1 3.5 17.8% -19.2% 0.77% -0.83% US 301 1a 9.3 9 10.1 -3.2% 8.6% -0.30% 0.80% US 301 1b 9.2 7.9 -14.1% -1.30% US 301 1c 9.5 9.2 -3.2% -0.30% US 301 2a 6.5 6.8 6 4.6% -7.7% 0.30% -0.50% US 301 2b 8.3 6.1 -26.5% -2.20% US 301 2c 6.5 6.4 -1.5% -0.10% US 301 3a 4.7 5.8 5.1 23.4% 8.5% 1.10% 0.40% US 301 3b 5.9 4.7 -20.3% -1.20% US 301 3c 7.3 6.5 -11.0% -0.80% US 301 4a 6.4 6.7 5.5 4.7% -14.1% 0.30% -0.90% US 301 4b 5.4 4.3 -20.4% -1.10% US 301 4c 5.1 4.2 -17.6% -0.90% US 301 5a 8.1 6.7 7.8 -17.3% -3.7% -1.40% -0.30% US 301 5b 5.3 4.7 -11.3% -0.60% US 301 5c 6.7 6.2 -7.5% -0.50% US 301 6a 6.6 6.9 7.1 4.5% 7.6% 0.30% 0.50% US 301 6b 7.9 7.9 0.0% 0.00% US 301 6c 6.3 5.5 -12.7% -0.80% US 301 7a 10.5 9.7 11.1 -7.6% 5.7% -0.80% 0.60% US 301 7b 10.0 10.8 8.0% 0.80% US 301 7c 8.0 6.9 -13.8% -1.10% US 301 8a 7.6 6.9 6.4 -9.2% -15.8% -0.70% -1.20% US 301 8b 7.2 7.1 -1.4% -0.10% US 301 8c 7.2 6.5 -9.7% -0.70% US 301 9a 7.6 8.1 7.1 6.6% -6.6% 0.50% -0.50% US 301 9b 7.9 6.9 -12.7% -1.00% US 301 9c 8.3 8.2 -1.2% -0.10% US 301 10a 8.3 8 8.1 -3.6% -2.4% -0.30% -0.20% US 301 10b 9.0 7.9 -12.2% -1.10% US 301 10c 7.5 6.1 -18.7% -1.40%

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46 Figure 5-2. Nuclear Versus ASTM TDR Water Content. 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 0.02.04.06.08.010.012.014.0 Oven Dry Moisture (%) TDR and Nuclear Moisture (%) TDR Nuclear 1:1 line Figure 5-1. Speedy Versus ASTM TDR Water Content. 0.0 3.0 6.0 9.0 12.0 15.0 0.02.04.06.08.010.012.014.0 Oven Dry Moisture (%) TDR and Speedy Moisture (%) TDR Speedy% 1:1 line

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47 Table 5-4. Dry Density w ith Speedy Comparison Results. Location Test Oven d TDR d Speedy d % error TDR % error Speedy Absolute TDR Absolute Speedy I-4 1a 112.1 103.9 110.5 -7.3% -1.4% -8.20 -1.60 I-4 1b 115.7 114.2 -1.3% -1.50 I-4 2a 105.9 102.1 105.2 -3.6% -0.7% -3.80 -0.70 I-4 2b 109.7 108.9 -0.7% -0.80 I-4 3a 108.6 102.8 108.0 -5.3% -0.6% -5.80 -0.60 I-4 3b 111.4 110.9 -0.4% -0.50 US 301 1a 111.9 109.6 113.9 -2.1% 1.8% -2.29 1.98 US 301 1b 112.1 113.0 0.8% 0.93 US 301 1c 110.7 111.6 0.8% 0.92 US 301 2a 110.2 106.1 109.4 -3.8% -0.7% -4.13 -0.82 US 301 2b 106.8 108.2 1.3% 1.40 US 301 2c 107.5 106.4 -1.0% -1.10 US 301 3a 109.1 104.6 109.0 -4.1% -0.1% -4.47 -0.10 US 301 3b 106.3 106.4 0.1% 0.10 US 301 3c 108.3 111.1 2.6% 2.80 US 301 4a 111.3 105.1 110.9 -5.6% -0.4% -6.18 -0.42 US 301 4b 112.1 111.0 -1.0% -1.16 US 301 4c 109.4 108.7 -0.7% -0.72 US 301 5a 109.9 105.9 108.8 -3.6% -1.0% -4.00 -1.11 US 301 5b 105.4 104.7 -0.7% -0.70 US 301 5c 109.5 108.9 -0.6% -0.61 US 301 6a 108.3 106.2 111.5 -1.9% 3.0% -2.06 3.24 US 301 6b 107.0 106.9 -0.1% -0.10 US 301 6c 111.2 111.1 -0.1% -0.10 US 301 7a 112.6 110.8 113.0 -1.6% 0.4% -1.78 0.41 US 301 7b 112.3 117.0 4.2% 4.68 US 301 7c 113.1 118.0 4.2% 4.81 US 301 8a 110.8 106.2 111.1 -4.1% 0.3% -4.58 0.31 US 301 8b 109.7 109.3 -0.4% -0.41 US 301 8c 107.1 106.7 -0.4% -0.40 US 301 9a 112.8 108.1 112.4 -4.2% -0.4% -4.73 -0.42 US 301 9b 113.3 112.8 -0.4% -0.42 US 301 9c 114.5 114.3 -0.2% -0.21 US 301 10a 111.2 108.0 111.2 -2.9% 0.0% -3.17 0.00 US 301 10b 109.4 110.4 0.8% 0.91 US 301 10c 112.5 111.9 -0.5% -0.52

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48 Table 5-5. Dry Density with Nuclear Comparison Results. Location Test Oven d TDR d Nuclear d % error TDR % error Nuclear Absolute TDR Absolute Nuclear I-4 1a 112.1 103.9 111.7 -7.3% -0.4% -8.20 -0.40 I-4 1b 115.7 114.7 -0.9% -1.00 I-4 2a 105.9 102.1 105.8 -3.6% -0.1% -3.80 -0.10 I-4 2b 109.7 109.7 0.0% 0.00 I-4 3a 108.6 102.8 109.4 -5.3% 0.7% -5.80 0.80 I-4 3b 111.4 112.1 0.6% 0.70 US 301 1a 111.9 109.6 111.1 -2.1% -0.7% -2.29 -0.81 US 301 1b 112.1 113.4 1.2% 1.35 US 301 1c 110.7 111.0 0.3% 0.30 US 301 2a 110.2 106.1 110.8 -3.8% 0.5% -4.13 0.52 US 301 2b 106.8 109.0 2.1% 2.22 US 301 2c 107.5 107.6 0.1% 0.10 US 301 3a 109.1 104.6 108.7 -4.1% -0.4% -4.47 -0.42 US 301 3b 106.3 107.5 1.1% 1.22 US 301 3c 108.3 109.1 0.8% 0.81 US 301 4a 111.3 105.1 112.2 -5.6% 0.9% -6.18 0.95 US 301 4b 112.1 113.3 1.1% 1.18 US 301 4c 109.4 110.4 0.9% 0.95 US 301 5a 109.9 105.9 110.2 -3.6% 0.3% -4.00 0.31 US 301 5b 105.4 106.0 0.6% 0.60 US 301 5c 109.5 110.0 0.5% 0.52 US 301 6a 108.3 106.2 107.7 -1.9% -0.5% -2.06 -0.51 US 301 6b 107.0 107.0 0.0% 0.00 US 301 6c 111.2 112.0 0.8% 0.84 US 301 7a 112.6 110.8 112.0 -1.6% -0.5% -1.78 -0.61 US 301 7b 112.3 111.5 -0.7% -0.81 US 301 7c 113.1 114.3 1.0% 1.16 US 301 8a 110.8 106.2 112.0 -4.1% 1.1% -4.58 1.25 US 301 8b 109.7 109.8 0.1% 0.10 US 301 8c 107.1 107.8 0.7% 0.70 US 301 9a 112.8 108.1 113.4 -4.2% 0.5% -4.73 0.53 US 301 9b 113.3 114.3 0.9% 1.06 US 301 9c 114.5 114.6 0.1% 0.11 US 301 10a 111.2 108.0 111.4 -2.9% 0.2% -3.17 0.21 US 301 10b 109.4 110.6 1.0% 1.12 US 301 10c 112.5 113.9 1.3% 1.48

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49 Figure 5-4. Nuclear Vers us ASTM TDR Dry Density. 100 104 108 112 116 100102104106108110112114116 Nuclear/Oven Dry Density (pcf)TDR and Nuclear Dry Density (pcf) TDR Nuclear 1:1 line Figure 5-3. Speedy Nuclear Ve rsus ASTM TDR Dry Density. 100 102 104 106 108 110 112 114 116 118 120 102104106108110112114116118 Nuclear/Oven Dry Density (pcf)TDR and Nuclear/Speedy Dry Density (pcf) TDR Speedy 1:1 line

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50 Table 5-3 and 5-4 summarizes the corresponding ASTM TDR dry density measurements, dry density back calculated using the wet nuclear density and the speedy moisture content, and dry density back calcu lated using the wet nuc lear density and the nuclear moisture content along with the dry de nsity back calculated using the wet nuclear density and the oven dry water content. Th e values were compared and percent and absolute error were calculated. All data points for both the nuclear and ASTM TDR tests were plotted in Figures 5-3 and 5-4 along with a 1:1 line. Water Content Measurement Discussion The water content measurement comparis on displayed in Table 5-2 shows the absolute error for both the ASTM TDR and nuclear methods varied similarly (TDR varied between -0.01 and 0.01 while the nucl ear varied between -0.02 and 0.01). The speedy moisture was slightly more variable with a range of -0.04 and 0.01. A graphic representation of scatter for speedy, nuclear and TDR methods compared to the oven dry method is displayed in Figures 51 and 5-2. It can be seen in both view graphs that the TDR one-step method shows less scatter than both nuclear and speedy moisture content when compared to the baselin e oven dry water content. The study performed by Sallam et al. (2004) indicate d that the TDR two-step method is likely to under predict water content, but this trend was not apparent in the one-step method. Based on current data there is not sufficient evidence to say that the TDR one-step met hod either under or over predicts the moisture content. The ASTM TDR measurements have a higher correlation coefficient with the oven dry measurements th an the nuclear or the speedy measurements (0.897 for the TDR method compared to 0. 857 for the nuclear method and 0.334 for the speedy moisture). Dry Density Discussion Due to the fact that the baseline dry de nsity was calculated from a combination of the nuclear moist density and the oven dry moisture content the results should not be viewed as an unbiased assessment of the abso lute accuracy of the TDR method. Because the nuclear method represents cu rrent engineering practice, th e results presented in this

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51 chapter simply represent a comparison be tween TDR and the st andard engineering practice. If the true accuracy of the TDR method is needed the use of an independent point of reference for dry density is needed. This issue is addressed in more detail in Chapter 6. However, the results presente d above indicate that TDR dry density was consistently below the nuclear baseline va lue. In other words the TDR dry density provided a more conservative measurement than its nuclear counterpart. In addition, the results indicate that TDR measurements exhi bit more scatter than their nuclear gage counterpart, possibly due to the reasons cited above. Measurement Variability Study In an effort to study the variability of moisture content and dry density within a given site a series of field test were performed using the nuclear gage method on a compacted subgrade. Measurements of wate r content and density were taken every 20 feet for a 100 foot by 25 foot section of comp acted subgrade. Water content for each of the test locations were also determined by oven drying (ASTM D 2216). A summary of oven dry measurements and the nuclear gage de nsities are displayed in Table 5-6. The results from the field test for water content and dry density are plot ted in Figure 5-5 and 5-6 respectively. It can be seen from the site variability st udy that the site itself varies by 33 percent from the maximum to the minimum water cont ent measurements. In this particular study the maximum and minimum values were re corded only twenty f eet apart. It is evident that the spatial variab ility within the site is highe r than the difference between typical TDR and oven dry moisture recorded in Figures 5-1 a nd 5-2. For dry density the site varied by nearly 4.2 percent from the maximum to the minimum dry density measurements. Just as in the case of wate r content variability, both the maximum and minimum values were recorded only twenty feet apart. The spatial variability within the site is almost equal to the difference between typical TDR and nuclear densities recorded in Figures 5-3 and 5-4. This is a very valuable finding in terms of evaluating the implementation of the one-step TDR method. It can be argued that since the “erro r” in TDR measurement is

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52 smaller than the spatial variability within th e site, TDR is a reliable estimator of in-situ water content and dry density; however, more testing would be needed to certify the validity of this conclusion. Table 5-6. Testing Locations and Measurements. Test Position x y Oven Dry (%) Dry Density (pcf) 0 3 7.8 116.7 0 22 7.6 112.0 20 3 8.3 112.2 20 22 7.8 114.5 40 3 7.7 113.7 40 22 7.0 114.8 60 3 7.1 113.5 60 22 8.2 113.5 80 3 6.6 113.4 80 22 8.1 113.8 100 3 8.8 112.4 100 22 8.1 115.8 maximum 8.8 116.7 minimum 6.6 112.0 average 7.8 113.9 standard deviation 0.631 1.407 Figure 5-5. Water Content Variability Within a Site. 0 ft 20 ft 40 ft 60 ft 80 ft 100 ft 3 ft 22 ft 6.0 6.5 7.0 7.5 8.0 8.5 9.0 Oven Moisture (%)

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53 Summary Side-by side measurements comparing th e TDR method to the nuclear method for water content measurement on Florida construc tion soils indicate that the One-Step TDR Method displays less scatter th an the speedy and nuclear gaug e and as a result is likely more accurate with th e proper selection of calibration constants “a”, “b”, “c”, “d”, “f”, and “g”. It thus appears that the TDR method is more reli able than the nuclear and speedy method. This statement is an echo of the 2004 report which featured a field study on the ASTM TDR two-step method. Dry dens ity results were inconclusive, due to the lack of a comparative baseline. However, a comparison of the data scatter between methods is similar. In general the TDR dry density readings are mo re conservative than the other accepted method. Figure 5-6. Dry Density Va riability within a Site. 0 ft 20 ft 40 ft 60 ft 80 ft 100 ft 3 ft 22 ft 108.0 110.0 112.0 114.0 116.0 118.0 Nuclear Dry Density w/oven (pcf)

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54 CHAPTER 6 – SLURRY RE PLACEMENT METHOD Introduction One of the main issues currently impeding the accurate evaluation of the TDR accuracy (and other methods) is the lack of a standard against which to measure the density. TDR measurements cannot be evalua ted against sand cone, nuclear gage, or speedy moisture since the accuracy of these me thods remains, in itself, in question. While oven dry measurements are broadly accep ted as the “standard” for water content, no such method is available fo r in-place density. In order to compare the methods to a baseline, it is necessary to accurately determ ine the moisture content and in-place density of the tested material. Sand cone measurements are highly sensitive to densification of the standard sand. Nuclear density gages that rely on back scatter to measure moisture content are representative of the water content within only the top few inches of soil. The use of a reliable method for in-place density m easurement is, therefore, a crucial step in evaluating the accuracy of the TDR method. Principle The proposed slurry replacement method is used to determine soil density in the field. The principle behind the slurry repl acement method is very similar to the sand cone method in that a soil sample is excavated manually and its weight W measured. The only difference being that the volume V of the excavated soil is determined form the volume of bentonite slurry required to fill the hole rather than fine sand. The bulk unit weight and dry unit weight d of the in-place soil is given by: V W and 100 (%) 1 wd (6-1)

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55 Where w is the water content (%), which is determined in the laboratory using the oven dry method. The volume of the bentoni te slurry is determ ined by measuring its weight, at a known density wh ich is calibrated in its c ontainer prior to the test. Equipment The equipment developed for the new slurry replacement test includes: 1) Slurry replacement apparatus which consis t of a three liter glass bottle with a PVC ball valve attachment. 2) Clear plastic base plat e measuring 1515 inch. 3) One-gallon, plastic, air-tight c ontainer to collect soil samples. 4) Tools to dig a small hole in the field. 5) Balance with a capacity of 10 kg and a mi nimum readability of 1.0 g. A rugged field scale with leveling capab ilities is recommended. 6) Bentonite slurry mixed to an appropriated consistency. 7) Oven capable of maintaining a temperature of 230 9F (110 5C) or other equipment according to SD 108. 8) Miscellaneous: Small pick, hammer, ch isels, spoons, pans or other suitable containers for drying moisture samples, buckets, plastic bags and paint brush. Figure 6.1 shows the assembly of the e quipment necessary for determination of the field unit weight. Figure 6-1. Assembly of Equipment for Slurry Replacement.

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56Equipment Fabrication and Calibration The equipment for the slurry replacem ent method was fabricated in the USF machine shop. The design called for a one inch hole to be centered on a inch clear acrylic base plate measuring 1515 inch. Th e base plate specification also called for 16 3 inch holes to be drilled out in each of the four corners. Further specifications called for the modification of a three-quarter inch CP VC threaded nipple such that it could be inserted into the opening of th e glass bottle. The threaded nipple was then fixed to the glass bottleneck with a one minute instant-mix epoxy. Equipment calibration included determini ng the exact volume the glass jar that had been modified with a threaded nipple attachment. The glass jar was calibrated utilizing the water-filling met hod. The empty jar was weighed and recorded and then filled with tap water and once again weighed. The temperature of the water was also recorded so that density corre ctions could be applied. K nowing the empty weight along with the water filled weight and the corresponding water temperature, volume can be determined. This calibration process was repe ated three times to ensure accuracy. The volume of the calibrated glass jar was found to be 3055 cm3. Slurry Viscosities for Different Sand Gradations In order to accurately determine the volume of the soil excavation, provisions must be made by controlling the viscosity of the fluid (bentonite-cement slurry) to ensure that it does not permeate out of the hole and into the surrounding soil matrix. In an effort to set forth some standard slurry viscosity recommendations based on soil type and grade, a series of tests were ran usi ng trial-and-error on several different slurry mixes and sands. The testing process can be summarized as follows: 1) A 5.5 inch diameter acrylic test cel l with graduated marking was filled approximately half way with a sel ected sand grade (Figure 6-2). 2) Bentonite slurry was prepared in a ble nder and was carefully poured onto the sand surface (Figure 6-3). 3) The slurry level inside the test cell was then monitored for the next hour (Fig 6-4).

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57 Figure 6-4. Slurry Level Monitoring. Figure 6-3. Test Cell with Slurry on Top of Sand. Figure 6-2. Test Cell Filled with Sand.

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58 Table 6-1 displays the preliminary re commendations for various grades of sand based on the testing program outlined above. Table 6-1. Slurry Mix Ratios Based on Soil Type. Sieve Number Bentonite to Water Ratio Soil Description(s) Passes Retained 1:45 Fine grain sand 30 65 1:40 Fine grain sand 30 65 1:35 Medium grain sand 20 30 1:30 Medium grain sand 20 30 1:25 Coarse grain sand 6 20 1:20 Coarse grain sand 6 20 Testing Procedure The slurry replacement testing method can be summarized as follows: 1) At the location where the density is to be determined, level off the ground surface (Figure 6-5) and position th e hole size template such that it is centered on the leveled surface. Trace around the template with a screwdriver to mark the hole diameter. Remove the template and dig a hole with an opening size equal to that traced on the ground. The volume of th e excavated hole should not exceed 3000 cm3, the full capacity of the sl urry replacement jar. 2) Carefully place all the soil removed from the hole into the on gallon moisture can. Close the cap tightly so as not to lose any moisture (Figure 6-6). 3) Measure the weight Wf of the full jar on the field scale. 4) Center the base plate on the hole. Turn the slurry replacement apparatus upside down with the valve in the cl osed position. Slowly open the valve to ensure that all the slurry goes directly through the fill hole (Figure 6-7). Close the valve when the slurry makes contact with th e base plate. Measure the weight We of the partially empty jar using the field scale.

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59 Figure 6-7. Pour Slurry Through Base-plate Hole. Figure 6-6. Soil Excavation Process. Figure 6-5. Level and Smooth the Soil Surface.

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60 5) Bring all the equipment back to the laboratory. Determine the weight of the gallon container plus moist soil fr om the field (without the cap), Wsoil. 6) Place the moist soil from the field in the oven to dry for 24 hours. Calculate the moisture content and the dry unit weight. The procedure outlined above is time-cons uming, but gives an accurate value of density, and is thus an extremely valuable to ol in evaluating the accu racy of the various other methods. Calculations The following are the required calculations for determination of dry unit weight of field compaction by the slurry replacement method. 1) Calculate the unit weight of slurry. jar f slurryV W (6-1) 2) Calculate the volume of the hole in the field. slurry vavle e f fieldW W W V (6-2) 3) Calculate the moist field unit weight field can soil can field tV W W (6-3)

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61 4) Calculate the moisture content in the field. 100 (%) can dry can dry can wet can cW W W W w (6-4) 5) Calculate the dry unity weight in the field. 100 (%) 1, c field t field dw (6-5) Experimental Verification of Measurement Accuracy In order to properly eval uate the error in the result obtained from the slurry replacement method, a comparison must be made between the slurry method measurements and a calibrated soil volume. To consummate this task a testing program was employed where slurry replacement m easurements were taken under controlled laboratory conditions using two different types of ca librated control volumes. Concrete Control Volume Assembly The concrete control volume test was used to measure the accuracy in which the slurry replacement method could predict volume. The fabrica tion of the concrete control volume was a several part process. First, fo rmwork was constructed out of three-quarter inch plywood. The internal dimensions of the formwork measured 61515 inch. Once the formwork was completed, two 60 pound bags concrete where mixed and placed into the formwork. After the conc rete was allowed to cure for about an hour at room temperature a six inch diameter hole approxi mately 5 inches deep was excavated from the center of the concrete volume. Once the concrete had fully hardened, the formwork was removed and a two part fiberglass e poxy was applied to the top surface of the

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62 concrete control volume (Figure 6-8). Th e application of the epoxy was done to create a water-tight seal thus prevent moisture seepag e into the concrete por es. After sealing the concrete void with the epoxy its volume was de termined using the water-filling technique discussed previously. The volume was found to be 975 cm3. Concrete Control Volume Tests A series of slurry replacement tests were performed in order to calibrate the slurry replacement volume measurements agains t a pre-known volume. The tests were performed in the concrete c ontrol volume previously described. Figure 6-9 shows an assembly of the equipment use for volume calibration. Figure 6-9. Concrete Contro l Volume Test Equipment. Figure 6-8. Concrete Control Volume.

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63 The testing procedure can be summarized as follows: 1) 4000 mL of a 1:40 bentonite slurry mix wa s prepared and poured into the glass slurry replacement bottle. Special care was taken to make certain the bottle was filled exactly to the top. The weight of the full slurry bottle was then measured and recorded. 2) The clear acrylic base plate was placed on the concrete control volume and the ball valve was attached to the slurry bottle. 3) Slurry was poured into th e void through the centrally located hole in the base plate. After the slurry made contact with the base plate the jar was again weighed. 4) Calculations were then conducted to de termine the volume of the slurry used during the testing process. The volume of slurry used was then compared to the known void volume. Soil Control Volume Assembly A calibrated box with a four inch extens ion collar attachment (Figure 6-10) was designed and built to provide controlled conditions for slurry replacement testing. The control box, measuring 16 inch, was constructed using three-quarter inch plywood, fastened together with wood glue and ceramic screws. To prevent moisture absorption into the plywood, the box was lined with fiberglass strips and epoxy resin (Figure 6-11) creating an internal coating. Special attention was given to the corner connections by doubling-up two layers of fibe rglass insulation (Figure 6-12). The box was then filled with water and set aside for several days to make certain it was completely sealed and water tight. Figure6 10.ControlBoxwithExtensionCollar.

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64 The fiberglass installation process can be summarized as follows: 1) The inners surfaces were prepared by ensuring they were dust free and dry. 2) The fiberglass mats were cut into strips consistent with the internal dimensions of the box walls. 3) A two part epoxy resin was then mixed in accordance with the manufacturers specifications. 4) A thick layer of epoxy coating was applied to the inner surfaces with a two inch synthetic bristle brush. 5) The fiberglass strips were then positione d appropriately and pressed into the resin-coated surface. 6) A second layer of resin was then applie d over the top of the fiberglass strips. 7) Steps three through six were repeated un til the all the intern al surfaces were completely insulated. 8) The epoxy resin was allowed to harden and cure in accordance with the manufacturers specifications. 9) The box was then filled with water and set aside to en sure there were no leaks. Figure 6-12. Control Box Corner Detail. Figure 6-11. Fiberglass Resin, Material, and Tools.

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65Soil Control Volume Test The box was calibrated utilizing the wate r-filling method. The clean, dry, empty box was weighed and recorded. The box was th en filled with tap water and once again weighed. The temperature of the water was also recorded so that density corrections could be applied. Knowing the empty weight along with the wate r filled weight and corresponding water temperature, volume can be determined. This calibration process was repeated three times to ensure accuracy The volume of the calibrated control box was found to be 2.2917 ft3. Slurry Replacement Calibration Test A series of slurry replacement tests ha ve been performed on different sands in order to calibrate the slurry replacement m easurements against a pre-known density. The tests were performed in contro l box previously described. The testing procedure can be summarized as follows: 1) Each sand type was thoroughly mixed with water and covered for several hours to ensure an even distribution of moisture (Figure 6-13). 2) The compaction procedure consisted of the soil specimen being compacted in six layers, each approximately equal in thickne ss. A square, steel tamping plate (88 inches) was use to compact the soil (Figure 6-14). The under-compaction Figure 6-13. Soil Mixed with Water.

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66 process, as proposed by Ladd (1978), wa s used to produce a homogeneous soil volume (density) that could be used fo r comparative purposes. The number of tamps increased from 20 for the first layer to 25 for the last layer. 3) Following compaction of the six and final layer, the extension collar was removed and the soil specimen was carefully trimme d such that the soil surface was even with the top of the box (Figures 6-15, 6-16, and 6-17). Figure 6-15. Compacted Soil with Extension Collar Removed. Figure 6-16. Trimming the Excess Soil. Figure 6-14. Compacting the Soil in the Box.

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67 4) With the use of an over-head hoist, the fully compacted control box was placed onto a scale for weighing (Figure 6-18). Figure 6-18. Lifting the Soil Filled BoxUsingtheOver headHoist. Figure 6-17. Control Box Filled with Soil and Trimmed Flush.

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68 5) The weight of the soil filled box was th en determined using a 1000 lbs capacity scale with a readability of lb. Knowing the internal volume of the box, the weight of the empty box, and the weight of the box compacted with soil the wet density can be calcula ted (Figure 6-19). 6) A slurry replacement test was run inside the box, as a field measurement following the testing procedur e outlined above (Figure 6-20 ). Calculations were then performed to obtain th e dry density of the soil. 7) The oven dry moisture content was then determined for the soil in the in the control box. Knowing the so il wet density form step five and the water content the dry density of the soil in the box can be calculated. The absolute and normalized errors for the dry density measurements can be calculated as follows: 100 ) ( _, actual dry fromTDR dry dryError Absolute (6-6) 100 _, , fromTDR dry actual dry fromTDR dry dryError Normalized (6-7) Figure 6-19. Weighing the Box After Filling

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69 Experimental Verification Results and Discussion The final results are summarized in Tabl e 6-2. The results indicate that the accuracy in density measurements are typica lly less than 2% provided the proper slurry mix ratio is used. All data points for the soil control volume tests were plotted in Figure 6-21 along with a 1:1 line as well as a 1:1 line 2%. (a) Clear Plastic Template Placed Directly Over Hole. (b) Weighing the Full Slurry Bottle (c) Hole Filled to the Top with Bentonite Slurry Mixture. (d) Weighing the Slurry Bottle After Filling the Hole. Figure 6-20. Slurry Replacement Procedure Used for Soil Control Volume Calibration.

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70 Table 6-2. Results of Slurry Replacement Calibration Test.

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71 Field Testing Program A series of side-by-side test s (Figure 6-22) were carried out at two locations in the Tampa area using the nuclear gauge, TDR one-s tep method, and the slurry replacement method. TDR calibration values for were de termined using the cal ibration procedures outlined in chapter three. These unique cal ibration constants were used for all site specific TDR measurements. Figure 6-22. Side-by-Side Testing Figure 6-21. Slurry Replacement Density Versus Actual Density. 90 95 100 105 110 115 12 0 9095100105110115120 Actual Dry Density (pcf)Slurry Replacement Dry Density (pcf ) 1-25-C 1-30-C 1-35-C 1-30-M 1-35-M 1-40-M 1-45-M 1-30-F 1-45-F 1-50-F 1:1 line 1:1 line +2% 1:1 line -2%

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72Field Test Result and Discussion A summary of the test locations and soil types for the nuclear and One-Step TDR comparison is displayed in Table 6-3. Te sting was carried out a highway interchange project and a pipeline backfill site. Several tests were run at each location. All samples tested were common construction soils en countered in Florida (A-3 sands). Table 6-3. Testing Locations and Information. Location No. of TDR No. of Nuclear No. of Slurry B/W ratio Soil Type(s) Airport 5 5 5 1/30 A-3 (96% pass #60) USF-1 5 0 5 1/30 A-3 (87% pass #60) USF-2 2 0 2 1/45 A-3 (87% pass #60) Table 6-4 summarizes the corresponding dr y density back calculated using the wet nuclear density and the nuclear moisture content, TDR one-step dry density, along with the slurry replacement dry density measurements. The values were compared and percent and absolute error were calculated. All data points for both the nuclear and TDR one-step tests were plotted in Fi gures 6-23 along with a 1:1 line. Table 6-4. Dry Density Comparison Results.

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73 The results indicate that both TDR and nuclear gage underestimated the dry density when compared to the slurry repla cement method. However these results should be viewed with caution. As reported in Table 6-3 a 1:30 bentonite to water ratio was used at each site. This slurry ratio was se lected because site specific soil information at the time of the test was unknown. After the tests were performed, samples were brought back to the lab and a sieve analysis was conduc ted. The results showed that the both the airport and USF sites were comprised of fine grain sand, thus the a ppropriate slurry ratio was not used for the tests. It is known from the soil control volume test that when inappropriate slurry viscosities are used th at the dry density can be over estimate by as much as 5%. It is therefore hypothesized that the 1:1 line in Figure 6-23 should be shifted down by a factor of 5% to account for the use of the wrong slurry viscosity. In an effort to validate the proposed hypot hesis three more tests were conducted at the same USF site utilizing the appropriate sl urry mix for fine grain sands (1:45). The results are plotted in Figure 6-24 along with the original density data points and the Figure 6-23. Nuclear and TDR Density Versus Slurry Replacement Density. 90 95 100 105 110 115 120 9095100105110115120 Slurry Replacement Dry Density (pcf)TDR and Nuclear Dry Density (pcf) Nuclear TDR 1:1 line 1:1 line -5%

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74 shifted 1:1 line. The results indicate that the hypothesis is valid. It can be seen that the three new data points (denoted by the open squares) fall within the same range as the original data. The results also give an indication the TDR density measurements may be more accurate than the nuclear gage readings. Further observation shows that the nuclear gage readings typically over estimate the dry density. These finding could have huge implications in terms of quality control issues for passing and failing a compacted fill project. In order to certify the validity of this conclusion more testing would be needed. In an effort to provide the exit user of the slurry replacement method with a means of determining which slurry viscosity is appropriate for their respective sand type a relationship between the bentonite to water ratio and the effective particle size D10 was developed (Figure 6-25). The relationship was developed directly from the result of the soil control volume test which provided an id ea of the appropriate slurry viscosity per sand type. Figure 6-24. Hypothe sis Validation Plot. 90 95 100 105 110 115 120 9095100105110115120 Slurry Replacement Dry Density (pcf)TDR and Nuclear Dry Density (pcf) TDR (old) TDR (new) Nuclear (old) 1:1 line 1:1 line -2% 1:1 line +2%

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75 Summary A baseline dry density measurement procedur e was developed so that the absolute accuracy of the TDR method and that of other standard testing methods could be evaluated. Experimental verification of the methods accuracy under controlled laboratory conditions was conducted. Resu lts indicate that the method was accurate within 2%. A field testing program was empl oyed where several side -by-side field tests were performed to evaluate the One-Step TDR Method as well as the nuclear method against the baseline slurry-replacement measur ement. Results indicate that TDR may be more accurate. It also appears that the nucle ar gage readings will typically overestimate the dry density. Figure 6-25. Slurry Viscosity Ba sed on Effective Particle Size D10. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Bentonite-Water RatioEffective Size (D 10) 1/40 1/35 1/3 0 1/50 1/45

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76 CHAPTER 7 – SUMMARY, CONCLU SIONS, AND RECOMMENDATIONS Summary A brief review of time domain reflectom etry and its path to the field of geotechnical engineering was pe rformed. Also covered in some detail were the basic principles behind the One-Step TDR Method. Testing was carried out to evaluate the soil specific calibration of TDR constants. As a result, a greater unders tanding of the soil specific TDR constants has been achieved. The accuracy of the TDR one-step method was compared to that of current geotec hnical standard tes ting methods used by engineering practitioners. Also, an objectiv e and independent reference for measuring dry density was developed and served as a va luable tool in determining the absolute accuracy of the TDR and nuclear methods. This research has lead to a greater understanding of the One-Step TDR Method a nd will aid in its eventual widespread usage throughout the geotechnical field. Conclusions Investigation into the soil specific TDR calibration constants proved to be valuable. Soil constants “a” and “b” were found to behave cons istently with previous studies. It appears that soil constant “c” is a unique point for a given soil and it may be possible to catalog values based on soil type. For typical construction soils in Florida, and in the absence of soil-sp ecific calibration data, a value of 0.01 should be used for constant “c”. Soil constant “d” was demonstrated to change systematically with pore fluid conductivity as previous research had indicated. Soil constants “f” and “g” change with the pore fluid conductivity of the soil since they are calculated from constant “a”, “b”, “c”, and “d”. Constant “g” behaves, in general, similar to constant “d.” It is also noted that for a calibration plot of the di electric constant and the bulk electrical conductivity there may exist a un ique point at the dry conditio n for a particular soil at

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77 which true calibration lines intersect. Al so a parametric study on the calibration constants revealed that both the water conten t and the dry density are greatly affect with little variation of the soil constant “d”. This is a significant finding and further validates the need for a soil-specific field calibration to accurately determination of constant “d”. Several tests were performed side-byside using the One-Step TDR Method, nuclear gage, and speedy moisture. Data wa s compared for both moisture content and dry density measurement. Results indicate th at the TDR method displays less scatter than the nuclear method for moisture content measurement and may be more accurate with the proper selection of calibration constants. Dr y density results showed that the TDR onestep measurements displayed larger scatter but consistently yielded lower densities than the nuclear density/speedy moisture measuremen ts, and are therefore more conservative. Spatial analysis of the water content and dr y density within a give n site was studied. Results indicate that the site itself has a si gnificant variation rela tive to the variation between the various methods. A baseline dry density measurement procedur e was developed so that the absolute accuracy of the TDR method and that of ot her standard testing methods could be evaluated. A field testing program was empl oyed where several side -by-side field tests were performed to evaluate the One-Step TDR Method as well as the nuclear method against the baseline slurry-replacement measur ement. Results indicate that TDR may be more accurate. It also appears that the nucle ar gage readings will typically overestimate the dry density. Research carried out further validates the TDR method as a viable tool for geotechnical measurement. A greater understand ing of the soil specific constants used in conjunction with the one-step TDR method was also achieved. The results of studies carried out to evaluate the effects of por e fluid conductivity on calibration will be valuable to establishing the one-step TDR me thod as a reliable geotechnical measurement system.

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78Recommendations In the absence of soil-specific calibration information, a valu e of 1.00 should be used for soil constant “a” and a value of 8.50 for soil constant “b” for sandy construction soils (A3, A-1-b and A-2-4 soils) in the state of Flor ida. For A-2-4 soils, the percent fines must be below 15%. Also, a value of 0.01 should be used for soil constant “c” for both A-3 and A-1-b soils. The value of “d” can be determined by performing a single calibration test for the soil at a high value of water c ontent, typically between 20% and 25%. Table 7-1 presents a summary of the recommende d TDR calibration constants for use with Florida soils in the absence of a soil-specific calibration. Table 7-1. Recommended Values of TDR Calibration Constants. Lower values of c are associated with small percentages of fines, and vice versa. + Higher values of d are associated with high pore fluid conductivity (or high salt content), and vice versa Further routine evaluation relating to the one-step me thod should be focused on building a history of the range of each constant and its rela tion to soil classification and gradation. Testing soils with higher fines would be of use and is needed to validate the conclusions made herein for sands. The eval uation of measurement variability within a site must also be addressed in routine eval uations of TDR, nuclear and other methods. Also, a testing program involving the slurry replacement method, TDR one-step method and traditional methods would be of bene fit in validating the method’s accuracy. Soil Type a b c* d+ A-1-b 1.0 8.50 0.01 0.2 to 0.5 A-2-4 1.0 8.50 0.02 to 0.05 0.3 to 0.5 A-3 1.0 8.50 0.01 0.3 to 0.7

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79 REFERENCES Alharthi, A., and Lange, J. (1987), “Soil Wa ter Saturation: Dielectric Determination,” Water Resources Research, Vol. 23, pp. 591-595. Baker, J.M., and R.R. Allmaras. (1990), “S ystem for Automating and Multiplexing Soil Moisture Measurement by Time Domain Reflectometry,” Soil Science Society of America Journal, Vol. 54, No. 1, pp. 1-6. Dalton, F. N., Herkelrath, W. N., Rawlins, D. S. and Rhoades, J. D. (1984), “Time Domain Reflectometry: Simultaneous Measurem ent of Soil Water Content and Electrical Conductivity with a Single Probe,” Science, New Series, Vol. 224, No. 4652, pp. 989990. Dasberg, S. and Dalton, F. N. (1985), “Tim e Domain Reflectometry Field Measurement of Soil Water Content an d Electrical Conductivity,” Soil Science Society of America Journal, Vol. 49, pp. 293-297. Dirksen, C, and Dasberg, S., (1993), “Improved Calibration of Time Domain Reflectometry Soil Water Content Measurements,” Soil Science Society of America Journal, Vol. 57, pp. 660-667. Drnevich, V. P., Lin, C., Quanghee, Yi, Yu, X., Lovell, Janet, (2000), “Real-Time Determination of Soil Type, Water Conten t, and Density Using Electromagnetics,” Final report, FHWA/IN/JTRP-2000/20. Drnevich, V.P., Yu, X., and Lovell, J. ( 2002). “A new method for water content and insitu density determination.” Proceedings of the Great Lakes Geotechnical and Geoenvironmental Conference, Toledo, Ohio, May, 15p Drnevich, V. P., Yu, Xiong, Lovell, Janet, (2003), “Beta Testing Implementation of the Purdue Time Domain Reflectometry (TDR) Method for Soil Water Content and Density Measurement,” Final report, FHWA/IN/JTRP-SPR-2489. Drnevich, Vincent P., Yu, Xiong, Lovell, Janet and Tishmack, Jody, (2001), “Temperature Effects on Dielectric C onstant Determined by Time Domain Reflectometry,” Proceedings of the Second International Symposium and Workshop on Time Domain Reflectometry for Innovative Geotechnical Applications, Northwestern University, Evanston, Illinois, 2001.

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80 Fellner-Feldegg, J., (1969), “The Measurem ent of Dielectrics in Time Domain”. Journal of Physical Chemistry, Vol. 73, pp. 616-623. Feng, W., Lin, C. P., Deschamps, R. J. a nd Drnevich, V. P. (1999), “Theoretical Model of a Multisection Time Domain Reflectometry Measurement System,” Water Resources Research, Vol. 35, No. 8, pp. 2321-2331. Giese, K. and Tiemann, R. (1975), “Determination of the complex permittivity from thinsample Time Domain Reflectometry: Improved analysis of the syep response Wave form,” Adv. Mol. Relax. Processes, Vol. 7, pp. 45-59. Harison, J. A. (1989), “In -situ CBR Determ ination by DCP Testing Using a Laboratorybased Correlation,” Australian Road Research, Vol. 19, pp. 313-317. Heimovaara, T. J. (1993), “Design of Triple -Wire Time Domain Reflectometry Probes in Practice and Theory,” Soil Science Society of America Journal, Vol. 57, pp. 1410-1417. Heimovaara, T. J. and Bouten, W. (1990), “A Computer-Controlled 36-Channel Time Domain Reflectometry System for Monitoring Soil Water Contents,” Water Resources Research, Vol. 26, No.10, pp. 2311-2316. Herkelrath, W. N., Hamburg, S. P. and Mu rphy, Fred (1991), “ Automatic, Real Time Monitoring of Soil Moisture in a remote Fi eld Area with Time Domain Reflectometry,” Water Resources Research, Vol. 27, No. 5, pp. 857-864. Hilhorst, M. A. (2000), “A Pore Water Conductivity Sensor,” Soil Science Society of America Journal, Vol. 64, pp. 1922-1925. Kleyn, E. G. (1975), “The Use of the Dynamic Cone Penetrometer (DCP),” Transvaal Roads Department Report, No. L2/74. Krauss, J. D., (1984), “Electromagnetics ,” McGraw-Hill, New York. Ladd, C.C., 1978, “Preparing Test Sp ecimens Using Undercompaction,” Geotechnical Testing Journal, GTJODJ, Vol. 1, No. 1, pp. 16-23. Ledieu, J.P., Ridder, De., and Dautrebande A., (1986), “A Method for Measuring Soil Moisture Content by Time Domain Reflectometry ,” Journal of Hydrology, Vol. 88, pp. 319-328. Lin, C., Siddiqui, S.I., Feng, W., Drnevi ch, V., and Deschamp, R., (2000), “Quality Control of Earth Fills Using Time Domain Reflectometry (TDR)”, Constructing and Controlling Compaction of Earth Fills, ASTM STP 1384, D. W. Shankin, K. R. Rademacher, and J. R. Talbot. Eds., American Society for Testing and Materials, West Conshohocken, PA,2000.

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81 Malicki, M. A., Plagge, R. and Roth, C. H. (1996), “Improving the Calibration of Dielectric TDR Soil Moisture Determinati on Taking into Account the Solid Soil,” European Journal of Soil Science, Vol. 47, pp. 357-366. Malicki, M.A, Walczak, R.T., Koch, S. and Fluhler H. (1994). “Determining soil salinity from simultaneous readings of its electri cal conductivity and permittivity using TDR.” In. Proc. Symp. on TDR in Environmental, Infrastructure and Mining Applications, Evanston, IL. Spec. Publ. SP. 19-94, U.S. Dep. Of Interior Bureau of Mines, Washington DC., 328-336. Rhoades, J. D. and J. van Schilfgaarde (1976), “An Electrical Conductivity Probe for Determining Soil Salinity,” Soil Science Society of America Journal, Vol. 40, pp. 647651. Sallam, Amr M., White, Newel K. and Ashmawy, Alaa K. (2004), “Evalauation of the Purdue TDR Method for Soil Water C ontent and Density Measurement,” Final Report to the Florida Department of Transportation, Contract No. BC-353-30. April 2004. Siddiqui, S.I. and Drnevich, V.P., (1995), “Use of Time Domain Reflectometry for the Determination of Water Content and Density of Soil,” FHWA/IN/JHRP-95/9, Purdue University. Siddiqui, S.I., Drnevich, V.P. and Deschamps, R.J. (2000). “Time domain reflectometry development for use in ge otechnical engineering.” Geotechnical Testing Journal, 23(1), 9-20. Sihvola, A.H. (1999). “Electromagnetic Mi xing Formulas and Applications.” London: Institution of electrical engineers. Topp, G.C., Davis, J.L., and Annan, A.P. (1980), “Electromagnetic Determination of Soil Water Content and Electrical Conductiv ity Measurement Using Time Domain Reflectometry,” Water Resources Research, Vol. 16, pp. 574-582. Topp, G.C., Davis, J.L., and Annan, A.P. (1982), “Electromagnetic Determination of Soil Water Content and Electrical Conductivity Measurement Using TDR:II. Evaluation of Installation and Confi guration of Parallel Transmission Lines,” Soil Science Society of America Journal, Vol. 46, No. 4, pp. 678–684. White, Ian, Zegelin, Steven J. and Topp, G. C. (1994), “Effect of Bulk Electrical Conductivity on TDR Measurement of Wa ter Content in Porous Media,” USBM special publication SP 19-94, Washington, D.C.: U.S. Bureau of Mines, pp. 294-308.

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82 Yu, X. and Drnevich, V. P. (2004), “So il Water Content and Dry Density by Time Domain Reflectometry,” The Journal of Geotechnical and Geoenvironmental Engineering, ASCE, accepted for publication, to app ear in Vol. 130, Issue 9, September 2004. Zegelin, S. J., White, I. and Jenkins, D. R. (1989), “Improved Field Probes for Soil Water and Electrical Conductivity Measurement Using Time Domain Reflectometry,” Water Resources Research, Vol. 25, No. 11, pp. 2367-2376.

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83 BIBLIOGRAPHY Amente, G., Baker, John M. and Reece, C live F. (2000), “Estimation of Soil Solution Electrical Conductivity from Bulk Soil Electrical Conductivity in Sandy Soils,” Soil Science Society of America Journal, Vol. 64, pp. 1931-1939. Birchak, J.R., Gardner, C.G., Hipp, J.E., and Victor, J.M., (1974) “High Dielectric Constant Microwave Probes for Sensing Soil Moisture,” Proceedings IEEE, Vol. 62, pp. 93-98. Campbell, Jeffrey E. (1990), “Dielectric Prope rties and Influence of Conductivity in Soils at One to Fifty Megahertz,” Soil Science Society of America Journal, Vol. 54, pp. 332341. Clarkson, T. S., Glasser, L., Tuxworth, R. W., and Williams, G. (1977), “An appreciation of experimental factors in Time-Domain Sp ectroscopy,” Adv. Mol. Relax. Processes, Vol. 10, pp. 173-202. Mojid, M. A., Wyseure, G. C. L. and Ro se, D. A. (2003), “Electrical Conductivity Problems Associated With Time-Domaon Reflectometry (TDR) Measurement in Geotechnical Engineering,” Geotechnical and Geol ogical Engineering, Vol. 21, Is. 3, pp. 243-258. Nadler, A., Dasberg S. and Lapid, I. (1991) “Time Domain Reflectometry Measurements of Water Content and Electrical Conduc tivity of Layered Soil Columns,” Soil Science Society of America Journal, Vol.55, pp. 938-943. Noborio, K. (2001), “Measurement of Soil Water Content and Electrical Conductivity by Time Domain Reflectometry: A Review,” Computers and Electronics in Agriculture, Vol. 31, pp. 213-237. O’Connor, K., and Dowding, C., (1999), “GeoMeasurements by Pulsing TDR Cables and Probes” A book published by CRC Press LLC. Roth, C. H., Malicki, M. A. and Plagge R. (1992), “Empirical Evaluation of the Relationship Between Soil Dielectric Constant and Volumetric Water Content as the Basis for Calibrating Soil Moisture Measurements by TDR,” Journal of Soil Science, Vol. 43, pp. 1-13.

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84 Topp, G. C., Zeglin, S., and White, I. ( 2000), “Impacts of the Real and Imaginary Components of Relative Permittivity on Time Domain Reflectometry Measurements in Soils,” Soil Science Society of America Journal, Vol. 64, No. 4, pp. 1244-1252. Yanuka, M., Topp, G. C., Zegelin, S. and Zebc huk, W. D. (1988), “Multiple Reflection and Attenuation of Time Domain Reflectometry Pulses: Theoretical Considerations for Applications to Soil and Water,” Water Resources Research, Vol. 24, No.7, pp. 939-944.


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ABSTRACT: Traditional in-situ soil compaction monitoring methods are often limited in their application, thus quality control of compacted fills and roadway embankments remains a challenging problem. As a result, new methods are being developed to more accurately measure in-situ compaction parameters. Time domain reflectometry (TDR) is one such method. Several advances have been made over the past few years to further the use of TDR technology in water content and density measurement of compacted fill. The one-step method relies on the measurement of the apparent dielectric constant in conjunction with the bulk electrical conductivity, and correlates them through two soil-specific constants, f and g. The two measurements, together with other soil specific constants, are then used to back calculate the water content and density in a single step. However, questions remain regarding the accuracy and bias of TDR measurements in relation to other "established" in-situ procedures such as the nuclear gage and speedy moisture. Results from an experimental program to obtain calibration constants for typical sands used in roadway construction are presented. A number of side-by-side tests are performed to compare the measurements obtained using the TDR one-step method to those obtained form other methods. Conducting such side-by-side tests is a critical step in the progress and eventual widespread usage of the one-step method. In addition, all the results are compared against an independent measurement of the in-place density from a slurry-replacement method. The objective of the independent measurement is to provide a baseline for accurate and unbiased evaluation of TDR and other technologies.
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