[UCI]I804:21031-200000181361 Thes s for the e ree of o tor of h oso h o so to s s of st e oft e os ts o s er o st r e s h r e t e to h e e rt e t of e eer The r te hoo o to ers t e r r o so to s s of st e oft e os ts o s er o st r e s h r e t e to 연직배수재가 설치된 연약지반의 지반 수 sor rof Te h e thes s s tte rt f f e t of the re re e t for the e ree of o tor of h oso h e rt e t of e eer the r te hoo o to ers t e r r h e 의 공학박사 학위 주 심 공학박사 김 진 만 위 원 공학박사 김 태 형 위 원 공학박사 신 호 성 위 원 공학박사 안 재 훈 위 원 공학박사 김 윤 태 o so to s s of st e oft e os ts o s er o st r e s h r e t e to ssert t o h e ro e (Chairman) Kim, Jin Man (Member) Kim, Tae-Hyung (Member) Shin, Hosung (Member) Ahn, Jaehun (Member) Kim, Yun-Tae e r r TABLE OF CONTENTS TABLE OF CONTENTS. i LIST OF SYMBOLS AND UNITS. xiii SUMMARY IN KOREAN. xv LIST OF FIGURES .xvii LIST OF TABLES .xxii CHAPTER 1: INTRODUCTION .2 Purpose and application of vertical drains .3 Overview of PVD-improved construction works .4 Objectives and the scope of study .5 Organization of the thesis.
10 CHAPTER 2: LITERATURE REVIEW .1 History and Development of Vertical Drains .2 Parameters related to PVDs performance .1 Equivalent drain diameter .2 Mandrel Size and Shape.4 Drain spacing and influence zone .5 Soil disturbance caused by PVD installation and discharge capacity .3 Soil disturbance effect .1 Soil disturbance generation .2 Analytical models of soil disturbance .3 Estimation of the smear zone properties .4 Difference between experimental and field permeability in smear zone .1 Definition of discharge capacity of drain .2 Discharge capacity requirement of prefabricated vertical drains .1 Discharge capacity from drain resistance approach .2 Discharge capacity based on the discharge in the PVD.3 Discharge capacity reduction with depth and time .5 Theory of vertical consolidation .2 One-dimensional consolidation test .3 Calculation of the ultimate consolidation settlement .4 Secondary consolidation settlement .6 Theory of radial consolidation with vertical drain .2 Analytical solution considering smear zone effects .3 Analytical solution considering discharge capacity reduction effects .7 Large (finite) strain theory for radial consolidation .1 Large strain governing equation with radial flow .2 Relationship between large-strain effect and vertical strain .8 Plane strain consolidation model of PVD-installed deposit .1 One-Dimensional drainage elements (1-D drainage element) .2 Macro-element formulation (Sekiguchi et al.3 kve method (Chai et al.4 Modelling PVD in plane strain by solid element .1 Method of Shinsha et al.2 Method of Indraratna and Redana (1997) .3 Method of Kim and Lee (1997) .9 Finite element method in consolidation .1 Morh-Coulomb model .2 Soft soil model.1 Isotropic states of stress and strain 1' 2' 3' .2 Yield function for triaxial stress state 2' 3' . 67 CHAPTER 3: AN ANALYTICAL MODEL FOR CONSOLIDATION OF PVD- INSTALLED DEPOSIT CONSIDERING SOIL DISTURANCE .2 A simple analytical solution for an axisymmetric unit cell with soil disturbance71 3.1 A nonlinear distribution of hydraulic conductivity and compressibility .3 Analysis results and comparisons .3 Application to field behavior.4 Summary and conclusion. 95 CHAPTER 4: RADIAL CONSOLIDATION OF PVD-INSTALLED DEPOSIT iii WITH DISCHARGE CAPACITY REDUCTION USING LARGE STRAIN THEORY .2 A large-strain radial consolidation equation for PVD-installed deposits .3 Effects of various parameters on consolidation behavior .1 The discharge capacity reduction factor .2 Disturbance degree of hydraulic conductivity .3 The Cc/Ck ratio .4 Initial effective stress of a soft deposit.4 Application to a test embankment .1 A test embankment at Saga Airport .2 A consolidation test of large block sample .5 Summary and conclusions. 120 CHAPTER 5: CONSOLIDATION BEHAVIOR OF PVD-INSTALLED DEPOSIT CONSIDERING DISCHARGE CAPACITY REDUCTION WITH DEPTH .2 Analytical models of axisymmetric unit cell with a varied discharge capacity123 5.1 Varied discharge capacity with a nonlinear distribution .2 Comparison of solutions .3 A proposed k've method considering a varied discharge capacity .4 Verification of analytical models with varied discharge capacity with numerical analysis .5 Summary and Conclusion.
136 iv CHAPTER 6: AN EQUIVALENT PLANE STRAIN MODEL OF PVD- IMPROVED SOFT DEPOSIT CONSIDERING SOIL DISTURBANCE AND WELL RESISTANCE .2 Formulation of an equivalent 2-D model of PVD-installed deposit.1 Equivalent width of vertical drain in 2-D model .2 Equivalent horizontal permeability in 2-D model .3 Application to a test embankment .1 Test embankment on soft clay deposit in eastern China .2 Test embankment on soft clay in Malaysia .3 Comparison three-dimension (3-D) numerical simulation.4 Summary and conclusion. 165 CHAPTER 7: CONCLUSION AND RECOMMENDATIONS .1 An analytical model for consolidation of PVD-installed deposit considering soil disturbances .2 Radial consolidation of PVD-installed normally consolidated soil with discharge capacity reduction using large strain theory .3 Analysis of consolidation behavior of PVD-installed deposits considering a varied discharge capacity with depth .4 An equivalent plane strain model of PVD-installed Deposit .3 Recommendations for application in practice .4 Recommendations for future work. 203 vi LIST OF SYMBOLS AND UNITS a factor used to describe the hydraulic conductivity change (a = khw/kh) aw width of the prefabricated vertical drain (m) awx ratio of area in the axisymmetric model awpl ratio of the area in the equivalent 2-D plane strain model A dimensionless factor use to describe discharge capacity reduction degree with depth A1 dimensionless factor use to describe discharge capacity reduction degree with depth following Deng et al. (2013) A2 dimensionless factor use to describe discharge capacity reduction degree with depth following Deng et al.
(2013) Awpl areas of the drain in the equivalent plane strain model Asoilpl areas of the surrounding soil in the equivalent plane strain model b factor describe the ratio representing compressibility change (b = mvw/mv) bw equivalent plane-strain radius of the drain (m) B half width of plane strain unit cell (m) c cohesion of soil (kN/m2) Ck permeability index Cc compression index Cs swelling index vii Cd constant factor (= 3.54) in Chai et al. (2001)’s model Cf the hydraulic conductivity ratio between the field and laboratory values Cα secondary compression index ch coefficient of consolidation for horizontal drainage (m2/s) cv coefficient of consolidation for vertical drainage (m2/s) De diameter of influence zone (m) dw diameter of drain (well) (m) ds diameter of smear zone (m) e0 initial void ratio e current void ratio ef final void ratio ep void ratio at the end of primary consolidation f yield function of the Soft-Soil model Fn influence factors of PVD spacing Fs influence factors of smear zone Fr influence factors of well resistance Gs specific gravity H thickness of soil layer (m) Hdr drainage length (m) h head of water (m) viii i dimensionless hydraulic gradient k permeability coefficient of soil (m/s) kve equivalent vertical hydraulic conductivity in Chai et al. (2001) k've equivalent vertical hydraulic conductivity in author’s method ky vertical permeability coefficient in undisturbed zone (m/s) kh horizontal permeability coefficient in undisturbed zone (m/s) khp equivalent horizontal permeability coefficient in plane strain (m/s) khw horizontal permeability coefficient in disturbed zone at drain (m/s) kh(r) horizontal permeability coefficient in unit cell at radius r (m/s) ks horizontal permeability coefficient in smear zone (m/s) kw vertical permeability coefficient in drain (m/s) kw(t) vertical permeability coefficient in drain at time t (m/s) L PVD-improved length (m) mv volume compressibility coefficient of soil (kPa-1) mv(r) volume compressibility coefficient of soil at radius r (m2/kN) mvw volume compressibility coefficient of soil at drain (kPa-1) n ratio re/rw in axisymmetric condition OCR over consolidated ratio P(t) applied load at time t (kN/m2) PVDs prefabricated vertical drains ix q the radial flow of water in the soil mass qw drain discharge capacity (m3/s) qwo initial discharge capacity of drain (m3/s) qre required drain discharge capacity (m3/s) Q average quantity of water discharge per unit time (m3/s) Qin(t) total flow that enters the drain at time t from the surrounding soil (m3/s) R radial of influence zone (m); R = re r radius in unit cell (m) rw radial of drain (m) rs radial of smear zone (m) re radial of influence zone (m) rm Radius of mandrel (m) rtr radius of transition zone (m) S vertical drain spacing/ settlement (m) Sf final primary consolidation settlement (m) S0(t) consolidation settlement at time t in convective coordinates (m) t time (s, day) Th dimensionless time factor for horizontal drainage Tv dimensionless time factor for vertical drainage u excess pore water pressure (kN/m2) x ur excess pore water pressure at radius r in the unit cell (kN/m2) u0 initial excess pore water pressure (kN/m2) ur average excess pore water pressure for the unit cell (kN/m2) uw average excess pore water pressure at drain (kN/m2) Uh radial (horizontal) consolidation degree (%) Uv vertical consolidation degree (%) V volume of the soil mass (m3) vr velocity of flow (at radius r) (m/s) vx velocity of flow (at distance x) (m/s) w water content x distance from center of the drain in plane strain unit cell (m) z depth (m) Greek Letters factor used in Indraratna et al. (1997)’s model 1 factor reflecting the smear zone effects in Deng et al.
(2013) 2 factor reflecting the well resistance effects in Deng et al. (2013) factor used in Indraratna et al. (1997)’s model sat unit weight of saturated soil (kN/m3) w unit weight of water (kN/m3) xi v vertical strain (%) f final vertical strain (%) * modified swelling index * modified compression index factor in Hansbo’s solution poison ratio height in convective coordinate (m) o(t) height in convective coordinate at time t (m) Pi number 1,2,3 ' terms of principal stresses v' effective stress vo' initial effective stress vp' Preconsolidation pressure friction angle (degree) dilatancy angle factor of discharge capacity reduction (1/time) xii Consolidation Analysis of PVD-Installed Soft Deposits Considering Soil Disturbance and Discharge Capacity Reduction Author: Ba-Phu Nguyen Department of Ocean Engineering, the Graduate School, Pukyong National University ABSTRACT Prefabricated vertical drains (PVDs) combined with preloading are frequently used to accelerate rate of consolidation and gain shear strength in soft soils. PVD discharge capacity reduction and soil disturbance caused by PVD installation are important factors in ground improvement design, these factors significantly affect the consolidation behavior of PVD-improved ground.
In this thesis, a numerical solution for radial consolidation of PVD-installed deposits, formulates a general expression for discharge capacity reduction with consolidation process, is proposed based on large- strain theory. The effects of soil disturbance, such as a nonlinear distribution for radial hydraulic conductivity, are captured. The proposed solution was applied to a test embankment at Saga Airport and an experimental test. The predicted results of consolidation behaviors were in good agreement with observed data in all cases of the verification.
In order to perform a multi-drain analysis in numerical model, equivalent plane strain models were proposed. An equivalent vertical hydraulic conductivity ( kve' method) is proposed to consider the effects of PVD discharge capacity reduction xiii with increased confining pressure. The proposed method was validated via a test embankment on a thick soft ground for construction site in Busan New Port. The results indicated that it is necessary to consider the PVD discharge capacity reduction with depth on consolidation analysis.
A nonlinear distribution of discharge capacity with depth is recommended to use in practice. To realistically simulate existence of PVD in soft ground, an equivalent plane strain model using solid element was further proposed.