Microsoft Word Thesis Draft 2019 07 02 i ABSTRACT The radial (horizontal) coefficient of consolidation (cr) is a key parameter which impacts the total consolidation of the PVD improved grounds In prac[.]
ABSTRACT The radial (horizontal) coefficient of consolidation (cr) is a key parameter which impacts the total consolidation of the PVD-improved grounds In practice, the cr value can be interpreted from field tests and laboratory tests A radial consolidation test (RCT) might be conducted using incremental loading (IL) method with either a central drain (CD) or a peripheral drain (PD) The key goals of the research are: (1) to design and manufacture a multi-directional flow consolidometer (VCT, RCT-PD, RCT-CD) using incremental loading method; (2) to make a comparative study on the cr values obtained from the RCTIL using a PD and a CD; (3) to make a comparative study on the cr values derived from RCT-based method and CPTu-based method A desk study is carried out to secure the following: (1) a literature review on equipment used for the test and existing methods used to evaluate the cr value; (2) graphical design of a multi-directional flow consolidation cell Sampling and CPTu dissipation tests are carried out at sites Besides the basic physical lab tests, the RCT IL with a CD and a PD will be performed using the designed consolidation cell under same condition test Overall, the ratio of kr/kv is approximately equal the ratio of cr/cv The cr, PD & cr, CD are double to triple higher than cv The cr, CD values are about 1.5 times larger than figures of cr, PD Finally, the cr values determined from CPTu-based method are doubled higher than cr values obtained from RCT-based method The reliability of the new device is confirmed Moreover, the results of cr values in the case of both PD and CD obtained by interpreting with traditional method like square root time method is more reliable than non-graphical method The limitation of the study is that the amount of data is still limited so it is still not enough to fully confirm the reliability of the multi-directional flow consolidation cell In the future, the author intends to perform more consolidation and permeability tests to ensure that the new designated consolidation can be applied in routine performance i ACKNOWLEDGEMENTS I would like to express my sincere appreciation for the lecturers of Master of Infrastructure Engineering Program for their help during my undergraduate at Vietnam Japan University (VJU) My thesis supervisor Dr Nguyen Tien Dung for his enthusiasm, patience, advice and constant source of ideas Dr Dung has always been available to reply to my questions His support in professional matters has been priceless Special gratitude is given to LAS- XD 442 lab and the staff at Institute of Foundation and Underground, Golden Earth Inc for their kindly support for performing the laboratory work And finally, I want to spent my thank to my parents and friends for their unflinching support in the tough time Their support, spoken or unspoken, has helped me complete my master thesis ii TABLE OF CONTENTS ABSTRACT i ACKNOWLEDGEMENTS ii TABLE OF CONTENTS iii LIST OF FIGURES vii LIST OF TABLES ix LIST OF ABBREVIATIONS xi CHAPTER 1: INTRODUCTION 1.1 Background 1.2 Consolidation 1.2.1 Settlement with Prefabricated Vertical Drains (PVD) 1.3 Problem statement 1.4 Objectives and scope of present study CHAPTER 2: LITERATURE REVIEW 2.1 Fundamentals of One Dimensional Consolidation 2.1.1 Consolidation Theory with Vertical Drainage 10 2.1.2 Consolidation Theory with Horizontal Drainage 11 2.2 Consolidation Tests in Laboratory 15 2.2.1 Vertical oedometer consolidation test 15 iii 2.2.2 Horizontal Consolidation Test 16 2.3 Determination of Coefficient of Consolidation 17 2.3.1 Analysis of Time-Compression Curve 17 2.3.2 Graphical Method 18 2.3.2 Non-graphical Method 21 2.4 Falling Head Permeability Test 24 2.5 The piezocone penetration test (CPTu) 26 2.5.1 Introduction 26 2.5.2 Pore-water Dissipation Tests 27 2.5.3 Coefficient of Consolidation 28 CHAPTER 3: METHODOLOGY 32 3.1 Introduction 32 3.2 Radial Consolidation Test 33 3.2.1 Design of the equipment 33 3.2.2 Manufacture of the equipment 35 3.2.3 Testing procedure 37 3.2.4 Analysis procedure 38 3.3 Vertical consolidation test 38 3.3.1 Testing procedure 38 3.3.2 Analysis of Time-Compression Curve 38 3.4 Permeability test 39 3.4.1 Equipment of permeability test 39 3.4.2 Testing procedure 39 iv 3.4.3 Analysis procedure 40 3.5 CPTu dissipation test 41 3.5.1 Equipment 41 3.5.2 Testing procedure 42 3.5.3 Analysis procedure 42 3.6 Results verification and comparison 42 CHAPTER 4: TEST RESULTS & DISCUSSIONS 43 4.1 Introduction 43 4.2 Summary of test performed 43 4.3 Comparison of cr,PD and cv 46 4.3.1 Square root time method 46 4.3.2 Non-graphical method 47 4.3.3 Inflection point method 48 4.4 Comparison cr,CD and cv 49 4.4.1 Square root time method 49 4.4.2 Non-graphical method 50 4.4.3 Inflection point method 51 4.5 Comparison cr,PD and cr, CD 52 4.5.1 Square root time method 52 4.5.2 Non-graphical method 53 4.5.3 Inflection point method 54 4.6 Horizontal coefficient of consolidation (cr) from CPTu 55 4.6.1 Estimate cr value from monotonic dissipation curves 55 v 4.6.2 Estimate cr value from non-standard dissipation curves 59 4.7 Test verification 61 4.8 Comparison cr,PD, cr,CD vs cr, CPTu 62 CHAPTER 5: CONCLUSIONS & RECOMMENDATIONS 65 REFERENCES 68 vi LIST OF FIGURES Figure 1.1: Soil phase diagram (Das, 2008) Figure 1.2: Primary consolidation (Das, 2008) Figure 1.3: Typical oedometer settlement (Das, 2008) Figure 1.4: Settlement damage Figure 1.5: Drainage with and without drains Figure 2.1: Mechanism of consolidation Figure 2.2: Uv versus Tv relationship (Head, 1986) 11 Figure 2.3: Schematic diagram of an RCT with central drain and peripheral drain 11 Figure 2.4: (a) Scheme of arrangement of the consolidation test in the triaxial apparatus, with drainage towards the cylindrical surface; (b) Cylindrical element of the sample 12 Figure 2.5: Distribution of pore pressures within the soil sample related to r and t 13 Figure 2.6: Schematic of oedometer test (Head, 1986) 15 Figure 2.7: Schematic of the apparatus used for conducting radial consolidation test 16 Figure 2.8: Rowe cell test under equal strain loading, horizontal outward drainage 17 Figure 2.9: Shapes of consolidation curve gained from oedometer test 18 Figure 2.10: Theoretical curve linkage square-root time factor to degree of consolidation for vertical drainage (Taylor, 1942) 20 Figure 2.11: Consolidation curve relating square-root time factor to for drainage radially outwards to periphery with equal strain loading (Head, 1986) 21 Figure 2.12: (a) Theoretical Ur-log Tr curve for n = 5; (b) (dUr/d log Tr)-log Tr plot showing the inflection point (Sridhar and Robinson, 2011) 23 Figure 2.13: Falling-head permeability test (Das, 2017) 24 Figure 2.14: Principal sketch of horizontal and vertical trimming of samples from determining vertical and horizontal coefficient of permeability 25 Figure 2.15: Overview of the cone penetration test per ASTM D 5778 procedures 27 Figure 2.16: Strain path solution for CPTu1 dissipation tests (The and Houlsby, 1991) 30 Figure 2.17: Strain path solution for CPTu2 dissipation tests (The and Houlsby, 1991) 30 Figure 2.18: "Non-standard" dissipation curve ( Chai et al., 2012) 30 Figure 3.1: Equipment for radial consolidation test with peripheral drainage 33 vii Figure 3.2: Flow chart of the study 34 Figure 3.3: Equipment for radial consolidation test with central drainage 35 Figure 3.4: Manufacture of the equipment for radial consolidation with PD 36 Figure 3.5: Manufacture of equipment for radial consolidation test with CD 36 Figure 3.6: Radial consolidation with peripheral drain and central drain setup 37 Figure 3.7: Equipment of falling head permeability test 39 Figure 3.8: Falling head permeability test setup 40 Figure 3.9: The typical and complete electrical CPT system 42 Figure 4.1: Comparison of cv and cr,PD obtained from square root time method at 400 kPa & 800 kPa 46 Figure 4.2: Comparison of cv and cr,PD obtained from non-graphical method at 400 kPa & 800 kPa 47 Figure 4.3: Comparison of cv and cr,PD obtained from inflection point method at 400 kPa & 800 kPa 48 Figure 4.4: Comparison of cv and cr,CD obtained from square root time method at 400 kPa & 800 kPa 49 Figure 4.5: Comparison of cv and cr,CD obtained from non-graphical method at 400 kPa & 800 kPa 50 Figure 4.6: Comparison of cv and cr,CD obtained from inflection point method at 400 kPa & 800 kPa 51 Figure 4.7: Comparison of cr,PD and cr,CD obtained from square root time method at 400 kPa & 800 kPa 52 Figure 4.8: Comparison of cr,PD and cr,CD obtained from non-graphical method at 400 kPa & 800 kPa 53 Figure 4.9: Comparison of cr,PD and cr,CD obtained from inflection point method at 400 kPa & 800 kPa 54 Figure 4.10: Strain path solution for monotonic dissipation tests at 11 & 17m 57 Figure 4.11: Strain path solution for monotonic dissipation tests at 18.5 & 20.5m 58 Figure 4.12: Dilatory dissipation curve at 8.5m 59 Figure 4.13: Dilatory dissipation curve at 9.5 & 11.3 m 60 Figure 4.14: Results of test verification which compares the ratios between kr/kv with cr/cv 61 Figure 4.15: Comparison between cr,CPTu with cr,PD obtained from square root time method at 400 kPa 64 viii Figure 5.1 Comparison between results obtained from square root time, non-graphical and inflection point method at 400 kPa 67 Figure 5.2: Comparison between results obtained from square root time, non-graphical and inflection point method at 800 kPa 67 ix LIST OF TABLES Table 4.1: Laboratory and in-situ tests done 44 Table 4.2: Soil profile of borehole BH08 55 Table 4.3: Estimate cr value from modified time factor, T* 56 Table 4.4: Estimate cr values from “non-standard” dissipation curves 59 Table 4.5: Coefficient of permeability obtained from permeability tests 62 Table 4.6: Comparison cr,PD and cr,CD obtained by square root time method with cr,CPTu 63 x Figure 2.10: Theoretical curve linkage square-root time factor to degree of consolidation for vertical drainage (Taylor, 1942) 20 Figure 2.11: Consolidation curve relating square-root time factor to for drainage radially outwards to periphery with equal strain loading (Head, 1994) 2.3.2 Non-graphical Method Robinson (Robinson & Allam, 1998) proposed the inflection point method that the point of inflection, which is the point where the slope is maximum in an Ur- logTr plot, happen at a degree of consolidation of 63.2 % as shown in Figure 2.13(a) and Figure 2.13(b) The time, t63.2, matching to the point of inflection can be derived from a plot of (dS/dlogt) versus t plot, from which cr can be determined The inflection point method explained above can be simply plotted to derive the time corresponding to the point of inflection from a set of S-t data from a conventional consolidation test, without performing a graphical construction Robinson and Allam (Robinson & Allam, 1998) suggested a non-graphical matching method for interpreting the time corresponding compression data The settlement (S) collateral t is expressed as 21 S S0 U r S100 S0 (2.22) Where S0 and S100 are the settlement corresponding to the beginning and end of primary consolidation Substituting Eq (2.12) in Eq (2.22), we get 8Tr S S0 S100 S0 1 exp F n (2.23) A minimum of approximately consolidation curve are sufficient to calculate the values of S0, S100 and cr However, a non-linear regression may be implemented for obtaining better results 22 Figure 2.12: (a) Theoretical Ur-log Tr curve for n = 5; (b) (dUr/d log Tr)-log Tr plot showing the inflection point (Sridhar & Robinson, 2011) 23 2.4 Falling Head Permeability Test Figure 2.14 shows a schematic drawing of a falling head test setup For practical engineering purposes, the coefficient of permeability of clay is often depicted from one dimensional incremental loading oedometer compression tests (IL tests) The vertical coefficient of consolidation cv is obtained from the vertical compression modulus Mv and the vertical hydraulic conductivity kv (Larsson and Saăllfors, 1986): kv cv wav cv w 1 e Mv (2.24) where ɣw is the unit weight of water Applying the standard procedures for oedometer testing of clays, only the properties in the vertical direction are evaluated (Mv, kv and cv) Figure 2.13: Falling-head permeability test (Das & Sobhan, 2008) 24 However, in projects using prefabricated vertical drains (PVDs), consolidation is mainly carried out by the horizontal flow through the soil towards the drains, so it is preferable to conduct tests allowing for evaluation of horizontal coefficient of permeability kr and the horizontal coefficient of consolidation cr Figure 2.15 described method for trimming horizontal soil specimen to conduct permeability test In other expression, cr is defined as a function of Mr and kr: kr cr war cr w 1 e Mr (2.25) Vertical trimming for determining Horizontal trimming for determining vertical coefficient of permeability horizontal coefficient of permeability Figure 2.14: Principal sketch of horizontal and vertical trimming of samples from determining vertical and horizontal coefficient of permeability Natural soils are usually anisotropic in which the hydraulic conductivity in horizontal direction (kh) is often larger than that in vertical direction (kv) This characteristic is due to the fact that soils are deposited in layers Table 2.4 shows typical ratios of kh/kv from some natural soil types The hydraulic conductivity (k) of any given soil is function of void ratio, grain size distribution, viscosity of water, and in-situ temperature In cases of 25 involving effective stress changes, the void ratio changes with the changes of effective stress Thus, k depends on changes of effective stress Range of possible field values of kh/kv for fine-grained soil are ranged from to (Jamiolkowski, Ladd, Germaine, & Lancellotta, 1985) If the soil compressibility is isotropic (i.e., M v M r ), the interrelationship between the horizontal and vertical permeability can be expressed as: cv cr kv k r (2.26) 2.5 The piezocone penetration test (CPTu) 2.5.1 Introduction The piezocone penetration test (CPTu) is an in-situ testing method used to identify the geotechnical characteristics of soils and evaluate subsurface stratigraphy, relative density, strength and equilibrium groundwater pressures By using ASTM and international standards, tip resistance (qc), sleeve friction (fs), and pore-water pressure (u) are derived at different depth, as described in Figure 2.16 26 Figure 2.15: Overview of the cone penetration test per ASTM D 5778 procedures (P.W Mayne, 2007) 2.5.2 Pore-water Dissipation Tests Dissipation testing monitors pore water pressures as they dissipate with time A fulldisplacement device such as a cone penetrometer evaluates the appearance of additional pore water pressures (Δu) locally around the head of probe In clean sands, the Δu will decay rapidly because of the high hydraulic conductivity of sands, whereas in clays and silts of low hydraulic conductivity the measured Δu will take a noticeable time to equilibrate The static pore-water will eventually record to u0 Thus, the obtained porewater pressures (um) are a combination of transient and hydrostatic pressures, such that: um u u0 27 (2.27) During the permanent stop, the rate at which Δu declines with time It can be monitored and used to depict the coefficient of consolidation and permeability of the soil media Dissipation readings are regularly plotted on log scales; therefore, in clays with low hydraulic conductivity it becomes impractical to wait for full equilibrium that corresponds to Δu = and um = u0 A standard of practice is to record the time to achieve 50% dissipation, designated t50 2.5.3 Coefficient of Consolidation 2.5.3.1 Monotonic Dissipation For these cases, the strain path method (Teh, 1991) may be used to determine ch from the expression: T *a I R ch t50 (2.28) where t = corresponding measured time during dissipation (usually taken at 50% equalization), T* = modified time factor, IR = G/su = rigidity index soil and a = probe radius The strain path solutions (Teh, 1991) are described in Figure 2.18(a) and (b) for both midface and shoulder type elements in the case of monotonic dissipation response, respectively For clays, the rigidity index (IR) is the ratio of shear modulus (G) and shear strength (su) and may be calculated from different means including: (a) measured triaxial stressstrain curve, (b) measured pressuremeter tests, and (c) empirical correlation One correlation based on the index: 28 Ir G f (2.29) where τf (= su in undrained case) is shear strength at failure, was originally suggested by Vesic (Vesic, 1973) and it was associated with the assumed elastic ideal plastic behavior of soil That is, G is a constant value until plastic failure happens However, in modern soil mechanics G has been well recognized to degrade nonlinearly with the increment of induced shear strains Around a penetrometer, G varies from the maximum value (G0) at some distance from the penetrometer to much smaller value (G