Đề tài Statnamic testing of piles in clay

STATNAMIC TESTING OF PILES IN CLAY BY DUC HANH NGUYEN A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CIVIL AND STRUCTURAL ENGINEERING UNIVERSITY OF SHEFFIELD OCTOBER 2005 ii ABSTRACT A series of pile load tests have been carried out on an instrumented model pile installed in instrumented clay beds prepared in a 1-g calibration chamber under two stages of consolidation, i.e. one dimensional and triaxial consolidation. A variety of loading techniques (Constant Rate of Penetration at different rates, Maintained Load and Statnamic) have been applied during the model pile tests. On the basis of these tests, in conjunction with data from previous studies, shear rate effects in clay, i.e. the enhancement of soil shear resistance under high rates of shearing are highly non-linear. The available non-linear power laws for rate effects were applied to the test results to predict the static load-settlement curve from rapid load pile tests. It was found that these models can give a good prediction of the ultimate static pile capacity, but they overpredict the settlement at load below the ultimate value. Following this, an alternative method of deriving the static load- settlement curve from a rapid load pile test, a non-linear power law incorporating changing damping parameters, has been proposed. This method was used for the model pile tests and then it was calibrated for field load tests carried out on a full size instrumented pile installed in a stiff glacial till. A simple theoretical method, which was proposed by Randolph & Wroth (1978) to establish the relationship between the pile load and its settlement for static pile loads, was modified for static pile load tests and then developed for rapid pile load tests. The gradual decrease of the pile shaft resistance after its peak value to a residual pile shaft resistance, which is known as the softening effect, plus the changes of pore water pressures and the inertial behaviour of the soil around the pile were also reported and discussed. iii ACKNOWLEDGEMENTS The Author would like to express his deepest gratitude to his supervisors Prof. Bill Anderson and Dr. Adrian F.L. Hyde for their advice, encouragement and constant guidance throughout this research programme, and for their valuable time and efforts in shaping the framework of this thesis. Also, the Author take this opportunity to thank Prof. Bill Anderson and Dr. Adrian F.L. Hyde for their generosity in helping me when I had a difficulty in finance at the end of the study. The Author would like to thank technical staff at the University of Sheffield, particularly Mr. Paul Osborne and Mr. Mark Foster for their assistance throughout the experiments. Special thanks are due to Dr. Michel Brown for his guidance and advice on the laboratory experimental aspects of this work at the beginning of the research. Thanks are also due to academic staff in the Geotechnical Engineering Group for their friendship. Thanks are accorded to my friends for their assistance and sharing their experience. The Author would like to express his gratitude to David Lovegrove and his wife, for their support and encouragement throughout the study. I feel this country is much more beautiful with their friendship. Finally, grateful thanks are extended to the Vietnamese government for providing a full scholarship that enabled the Author to conduct this research. iv TABLE OF CONTENTS Page ABSTRACT ii ACKNOWLEDGEMENT iii TABLE OF CONTENTS iv LIST OF TABLES ix LIST OF FIGURES xi NOTATIONS AND ABBREVIATIONS xxiii CHAPTER 1 - INTRODUCTION 1.1 Background ……………………………………………………………………1 1.2 Research objectives……………………………………………………………2 1.3 Outline of thesis………………………………………………………………. 2 CHAPTER 2 - LITERATURE REVIEW 2.1 Introduction……………………………………………………………………4 2.2 Static load testing methods…………………………………………………….5 2.2.1 Maintained load test……………………………………………………...5 2.2.2 Constant rate of penetration test………………………………………….6 2.2.3 Osterberg load cell test…………………………………………………...7 2.3 Rate effects…………………………………………………………………….8 2.3.1 Rate effect studies using triaxial tests and torsion tests………………….9 2.3.2 Rate effect studies using direct shear tests……………………………...11 2.3.3 Rate effect studies using penetrometer and shear vane tests…………...13 2.3.4 Rate effect using a model instrumented pile in a clay bed……………...15 2.3.5 Results from field studies……………………………………………….16 2.4 Dynamic pile load tests……………………………………………………….18 2.4.1 The stress wave propagation equation………………………………….19 2.4.2 Pile dynamic resistance…………………………………………………20 v 2.4.3 Static pile capacity……………………………………………………...22 2.4.3.1 Case method of analysis……………………………………..……23 2.4.3.2 Signal matching method…………………………………………..23 2.4.4 Dynamic load test advantages and disadvantages………………………26 2.5 Statnamic load test……………………………………………………………26 2.6 Statnamic data interpretation…………………………………………………28 2.7 Quake values for shaft and toe resistances and the softening effect………….32 2.8 The changes of pore water pressure during pile installation and the subsequent loading stages…….............……………………………………..…………...37 2.9 Summary……………………………………………………………………...40 CHAPTER 3 - TESTING EQUIPMENT AND PROCEDURES 3.1 Introduction…………………………………………………………………..56 3.2 The calibration chamber……………………………………………………...57 3.3 Boundary effects……………………………………………………………...58 3.4 Bed preparation……………………………………………………………….60 3.4.1 Clay slurry preparation………………………………………………….60 3.4.2 Consolidometer…………………………………………………………61 3.4.3 Clay bed instrumentation……………………………………………….62 3.4.4 1-D consolidation……………………………………………………….63 3.4.5 Triaxial consolidation…………………………………………………..65 3.4.6 Pile installation………………………………………………………….68 3.5 Instrumented model pile……………………………………………………...69 3.5.1 Pile tip component……………………………………………………...69 3.5.2 Pile shaft sleeve component………………………………...…………..71 3.5.3 Actuator - Pile connection………………………………………………72 3.5.4 Pile shaft load cell performance…………………………………...……73 3.6 Servo-hydraulic loading system……………………………………………...73 3.7 Logging and control system………………………………………………….75 3.8 Instrumentation calibration…………………………………………………...76 3.9 Testing procedure…………………………………………………………….78 3.9.1 Constant rate of penetration tests……………………………………….78 3.9.2 Statnamic tests………………………………………………………….79 vi 3.9.3 Maintained load tests…………………………………………………...80 3.10 Bed dismantling……………………………………………………………..80 CHAPTER 4 - TESTING PROGRAMME 4.1 Introduction…………………………………………………………………101 4.2 Clay bed preparation and transducer locations……………………………..102 4.3 Constant rate of penetration tests (CRP tests)………………………………103 4.4 Statnamic tests (STN tests)………………………………………………….104 4.5 Maintained load tests (ML tests) …...………………………………………105 CHAPTER 5 - BED PROPERTIES 5.1 Introduction…………………………………………………………………114 5.2 Clay bed 1-D consolidation…………………………………………………114 5.3 Clay bed isotropic triaxial consolidation................…………………………117 5.4 Performance of the calibration chamber during the pile load tests…………117 5.5 Bed properties after the testing programme…………………………………119 CHAPTER 6 – PILE TEST DATA AND DISCUSSION 6.1 Introduction…………………………………………………………………139 6.2 Typical results of the pile load tests………………………………………..139 6.3 Pile shaft resistance results and models for the pile shaft resistance………..140 6.3.1 Non-linear models……………………………………………………..141 6.3.2 A new non-linear model for pile shaft rate effects…………………….145 6.3.3 Pile shaft softening effect……………………………………………...150 6.3.4 Repeatability of the static pile shaft resistances……………………….152 6.4 Pile tip resistance results…………………………………………………….153 6.5 Application of the proportional exponent model to the pile total load……...157 6.6 A simple theoretical approach for the load transfer mechanism……………158 6.6.1 Available models for load transfer…………………………………….158 vii 6.6.2 Modifications to the existing models for load transfer for static pile load tests and a new model for rapid load pile tests….............…...160 6.6.3 Application of the models to static pile load tests.……………………167 6.6.4 Application of the models to rapid load pile tests…..…………………168 6.6.5 Quake value for the pile shaft resistance of a rapid load test………….170 6.7 A comparison between maintained load tests and CRP tests……………….172 6.8 Pore water pressures around the pile during pile load tests…………………173 6.8.1 Pore water pressures during CRP tests at a rate of 0.01mm/s…………174 6.8.1.1 Pore water pressures at the pile shaft……………………………174 6.8.1.2 Pore water pressures around the pile shaft………………………175 6.8.1.3 Pore water pressures at the pile tip………………………………176 6.8.1.4 Pore water pressures below the pile tip………………………….176 6.8.2 Pore water pressures during maintained pile load tests……………….177 6.8.3 Pore water pressure regime during rapid load pile tests………………178 6.8.3.1 Pore water pressures at the pile shaft……………………………178 6.8.3.2 Pore water pressures around the pile shaft………………………178 6.8.3.3 Pore water pressures at the pile tip………………………………179 6.8.3.4 Pore water pressures below of the pile tip……………………….179 6.9 Clay bed inertial behavior…………………………………………………...179 CHAPTER 7 - FIELD LOAD TESTS 7.1 Introduction……………………………………………......................……..254 7.2 Ground conditions………………………......…………..…………………..254 7.3 Pile tests………………….........................…………………………………255 7.4 Prediction of the pile static capacity using the Unloading Point Method…..255 7.5 Application of the analyses to field tests…….....…………………….……..257 CHAPTER 8 - CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER WORK 8.1 Introduction……………………..........……………………………………..269 viii 8.2 Main conclusions…………………………………………..………………..269 8.3 Recommendations for further studies…………..…………………………...273 REFERENCES………………………………………………………………….275 ix LIST OF TABLES Table 2.1 Damping parameters in Dayal and Allen study Table 2.2 Case damping coefficient for different soil types Table 3.1 Speswhite kaolin properties as supplied by the manufacturers Table 3.2 Silica sand properties as supplied by the manufacturers Table 3.3 Silica flour silt properties as supplied by the manufacturers Table 3.4 Material for one clay bed Table 3.5 Material properties Table 4.1 Testing programme for Bed 1 Table 4.2 Testing programme for Bed 2 Table 4.3 Testing programme for Bed 3 Table 4.4 Testing programme for Bed 4 Table 4.5 Testing programme for Bed 5 Table 5.1 Volume of water expelled during 1-D consolidation Table 5.2 3-D consolidation degrees of Beds 1 to 5 Table 5.3 Undrained shear strengths of Bed 1 determined by hand vane tests Table 5.4 Undrained shear strengths of Bed 2 determined by hand vane tests Table 5.5 Undrained shear strengths of Bed 3 determined by hand vane tests Table 5.6 Undrained shear strengths of Bed 4 determined by hand vane tests Table 5.7 Undrained shear strengths of Bed 5 determined by hand vane tests Table 5.8 Moisture contents of Bed 1 Table 5.9 Moisture contents of Bed 2 x Table 5.10 Moisture contents of Bed 3 Table 5.11 Moisture contents of Bed 4 Table 5.12 Moisture contents of Bed 5 Table 5.13 Shear strengths from undrained triaxial tests Table 6.1 Static pile shaft resistance of Beds 2 to 5 Table 6.2 Pile tip loads for tests in Bed 1 Table 6.3 Pile tip loads for tests in Bed 2 Table 6.4 Pile tip loads for tests in Bed 3 Table 6.5 Pile tip loads for tests in Bed 4 Table 6.6 The influence of initial effects in the calculation for the pile settlement Table 7.1 Soil properties from laboratory tests for Grimsby clay Table 7.2 Grimsby soil description xi LIST OF FIGURES Figure 2.1 O-Cell Figure 2.2 Schematic arrangement of a Osterberg test Figure 2.3 Balderas-Meca’s test apparatus arrangement Figure 2.4 Damping coefficient, α, versus axial strain for monotonic consolidated undrained triaxial tests at different rates. (β=0.20; OCR=1) Figure 2.5 Half steel tube with semi-circular soil sample Figure 2.6 The shear device for the study of pile-soil interfaces Figure2.7 Penetrometer and soil container in experimental set-up Figure 2.8 (a) Schematic of the test arrangement (b) geometry of penetrometer for side friction tests Figure 2.9 Undrained peak strength measured from vane tests Figure 2.10 Slow and quick-penetration tests Figure 2.11 Shaft resistances and pile movements Figure 2.12 Wave propagation in a bar produced by an impact load Figure 2.13 Idealization of a pile as an elastic rod with soil interaction at discrete nodes Figure 2.14 Model of downward and upward waves due to soil interaction Figure 2.15 Smith Model for pile and soil Figure 2.16 Randolph & Deeks model for pile shaft and soil Figure 2.17 Randolph & Deeks model for pile tip and soil Figure 2.18 A typical statnamic loading-time relationship Figure 2.19 Statnamic device Figure 2.20 Forces acting on a pile during statnamic loading Figure 2.21 Unloading point method xii Figure 2.22 Load Settlement response Figure 2.23 Shaft quake values compared with the pile diameter Figure 2.24 Ramberg-Osgood model for the relationship of shaft resistance and displacement Figure 2.25 Idealised softening behaviour for a pile in clay Figure 2.26 Chandler & Martins’ test apparatus Figure 2.27 Strain Path Method to deep penetration in clays Figure 3.1 Strain distributions during pile installation according to the strain path method Figure 3.2 Pumping slurry to the consolidometer Figure 3.3 The consolidometer Figure 3.4 Miniature Druck Transducer Figure 3.5 Transducer arrangement in the calibration chamber Figure 3.6 Hole arrangement at the bottom plate Figure 3.7 The accelerometer and its protection Figure 3.8 1-D consolidation in the laboratory Figure 3.9 Schematic diagram of 1-D consolidation Figure 3.10 Loading plate and its o-rings in the laboratory Figure 3.11 Calibration chamber volume change units Figure 3.12 Removing the consolidometer after the finish of 1-D consolidation Figure 3.13 The calibration chamber sand retaining ring and its arrangement Figure 3.14 The triaxial calibration chamber membrane and drainage sand layer at the top of the clay bed Figure 3.15 The calibration chamber top plate and its attached membrane Figure 3.16 Top plate arrangement during 3-D consolidation Figure 3.17 Schematic diagram of 3-D consolidation xiii Figure 3.18 Using the casing tube and auger to make a hole in the bed for pile installation Figure 3.19 Schematic diagram of 3-D consolidation after pile installation Figure 3.20 Schematic diagram of the instrumented model pile Figure 3.21 The pile tip load cell Figure 3.22 The pore water transducer at the pile tip Figure 3.23 The pile shaft load cell Figure 3.24 The pore water transducer at the pile shaft Figure 3.25 Schematic diagram of the connection between the loading system and the pile for CRP and Statnamic tests Figure 3.26 The connection between the loading system and the pile for CRP and Statnamic tests Figure 3.27 Typical calibration results of a pore water pressure transducer Figure 3.28 Input loading pulse and actual loading pulse for a statnamic load test Figure 3.29 Schematic diagram of the connection between the loading system and the pile for maintained load tests Figure 3.30 The connection between the loading system and the pile for maintained load tests Figure 3.31 The clay bed when the tests had finished Figure 3.32 Carrying out hand vane tests and taking the samples for triaxial tests Figure 4.1 Transducer arrangement for Bed 1 Figure 4.2 Transducer arrangement for Bed 2 Figure 4.3 Transducer arrangement for Bed 3 Figure 4.4 Transducer arrangement for Bed 4 Figure 4.5 Transducer arrangement for Bed 5 xiv Figure 5.1 Bed settlements during 1-D consolidation Figure 5.2 Pore water pressure distribution during 280 kPa 1-D consolidation of Bed 1 Figure 5.3 Pore water pressure distribution during 280 kPa 1-D consolidation of Bed 2 Figure 5.5 Pore water pressure distribution during 280 kPa 1-D consolidation of Bed 4 Figure 5.6 Pore water pressure distribution during 240 kPa 1-D consolidation of Bed 5 Figure 5.7 The final transducer locations of Bed 1 Figure 5.8 The final transducer locations of Bed 2 Figure 5.9 The final transducer locations of Bed 3 Figure 5.10 The final transducer locations of Bed 4 Figure 5.11 The final transducer locations of Bed 5 Figure 5.12 Fluctuation of top and side cell pressures during a rapid pile load test Figure 5.13 Changes of pore pressures in the clay bed due to the drop of the top cell pressure Figure 5.14 Changes of pore pressures in the clay bed due to the drop of the top cell pressure over a period of 200ms Figure 6.1 Load-settlement curves for a CRP test at a rate of 0.01mm/s (B2/7/CRP-0.01) Figure 6.2 Load-settlement curves and pile penetration and velocity with time for a CRP test at a rate of 200mm/s. (B2/6/CRP-200) Figure 6.3 Load, settlement, pile velocity, and pile acceleration variation with time for a statnamic pile load test (B2/9/STN-35) Figure 6.4 Load – settlement curve and load and settlement variation with time for a maintained load test (B2/13/MLT) Figure 6.5 Skin friction load cell values for tests B1/1/CRP-0.01 and B1/2/CRP-100 Figure 6.6 Skin friction load cell values for tests B2/4/CRP-0.01 and B2/7/CRP-100 xv Figure 6.7 Skin friction load cell values for tests B3/21/CRP-0.01 and B3/18/CRP-100 Figure 6.8 Skin friction load cell values for tests B4/5/CRP-0.01 and B4/2/CRP-100 Figure 6.9 Skin friction load cell values for tests B5/15/CRP-0.01 and B5/14/CRP-100 Figure 6.10 Application of Gibson and Coyle’s model for pile load tests in Bed 2 (B1/1/CRP-0.01 and B1/4/STN-15) Figure 6.11 Application of Randolph and Deeks’ model for pile load tests in Bed 1 (B1/1/CRP-0.01 and B1/4/STN-15) Figure 6.12 Application of Balderas-Meca’s model for pile load tests in Bed 1 (B1/1/CRP-0.01 and B1/4 /STN-15) Figure 6.13 Application of Gibson and Coyle’s model for pile load tests in Bed 2 (B2/12/CRP-0.01 and B2/10 /STN-38) Figure 6.14 Application of Randolph and Deeks’ model for pile load tests in Bed 2 (B2/12/CRP-0.01 and B2/10/STN-38) Figure 6.15 Application of Balderas-Meca’s model for pile load tests in Bed 2 (B2/12/CRP-0.01 and B2/10/STN-38) Figure 6.16 Application of Gibson and Coyle’s model for pile load tests on Bed 3 (B3/6/CRP-0.01 and B3/5/CRP-100) Figure 6.17 Application of Randolph and Deeks’ model for pile load tests in Bed 3 (B3/6/CRP-0.01 and B3/5/CRP-100) Figure 6.18 Application of Balderas-Meca’s model for pile load tests in Bed 3 (B3/6/CRP-0.01 and B3/5/CRP-100) Figure 6.19 Application of Gibson and Coyle’s model for pile load tests in Bed 4 (B4/5/CRP-0.01 and B4/2/CRP-100) Figure 6.20 Application of Randolph and Deeks’ model for pile load tests in Bed 4 (B4/5/CRP-0.01 and B4/2/CRP-100) Figure 6.21 Application of Balderas-Meca’s model for pile load tests in Bed 4 (B4/5/CRP-0.01 and B4/2/CRP-100) Figure 6.22 Application of Gibson and Coyle’s model for pile load tests in Bed 5 (B5/15/CRP-0.01 and B5/14/CRP-100) Figure 6.23 Application of Randolph and Deeks’ model for pile load tests in Bed 5 (B5/15/CRP-0.01 and B5/14/CRP-100) xvi Figure 6.24 Application of Balderas-Meca’s model for pile load tests in Bed 5 (B5/15/CRP-0.01 and B5/14/CRP-100) Figure 6.25 Application of Equation 6.6 for the ultimate pile shaft resistance (Bed 2) Figure 6.26 Application of Equation 6.6 for the ultimate pile shaft resistance (Bed 3) Figure 6.27 Application