Cone Penetration Testing in Geotechnical Practice. Tom Lunne Peter K. Robertson John J.M. Powell

Transcription

1 Cone Penetration Testing in Geotechnical Practice Tom Lunne Peter K. Robertson John J.M. Powell BLACKIE ACADEMIC & PROFESSIONAL An Imprint of Chapman & Hall London Weinheim New York Tokyo Melbourne Madras

2 PREFACE ACKNOWLEDGEMENTS SYMBOL LIST CONVERSION FACTORS GLOSSARY v ix xi xii xvi xxii 1. INTRODUCTION Purpose and scope General description ofcpt and CPTU Role of CPT in site investigation Historical background Mechanical cone penetrometers Electric cone penetrometers Thepiezocone 7 2. EQUIPMENT AND PROCEDURES Cone penetrometer and piezocone. 8? 2.2 Pushing equipment On land Over water Depth of penetration Test procedures Pre-drilling, on land testing Verticality Reference measurements Rate of penetration Interval of readings Depth measurements Saturation of piezocones Dissipation test Data acquisition Calibration of sensors Maintenance Choice of capacity of load cells Precision and accuracy Summary of performance checks and maintenance requirements CHECKS, CORRECTIONS AND PRESENTATION OF DATA Factors affecting measurements and corrections Pbre water pressure effects on q c and fs Filter location Effect of axial load on pore water pressure readings Temperature effects Inclination Calibration and resolution of errors Effect of wear

3 vi Correction for CPTU zeroed at the bottom of a borehole Presentation of results Measured parameters Derived parameters Additional information Checks on data quality STANDARDS AND SPECIFICATIONS ISSMFE International Reference Test Procedure for Cone Penetration Test (CPT) Swedish Geotechnical Society (SGF): Recommended Standard for Cone Penetration Tests (1993) Norwegian Geotechnical Society (NGF): Guidelines for Cone Penetration Tests (1994) ASTM: Standard Test Method for Performing Electronic Friction Cone and Piezocone Penetration Testing of Soils (1995) Dutch Standard: Determination of the Cone Resistance and Sleeve Friction of Soil. NEN5140 (1996) Recommendations INTERPRETATION OF CPT/PIEZOCONE DATA General factors affecting interpretation Equipment design In situ stresses Compressibility, cementation and particle size Stratigraphy Rate of penetration Pore pressure element location Soil stratigraphy Soil classification Interpretation in fine-grained soils State characteristics Soil unit weight Overconsolidation ratio In situ horizontal stress Strength characteristics Undrained shear strength Sensitivity Effective stress strength parameters Deformation characteristics Constrained modulus Undrained Young's modulus Small strain shear modulus Flow and consolidation characteristics Coefficient of consolidation Coefficient of permeability (hydraulic conductivity) Interpretation in coarse-grained soils State characteristics Relative density (density index) State parameter Overconsolidation ratio In situ horizontal stress Strength characteristics Effective stress strength parameters Deformation characteristics Young's modulus Constrained modulus Small strain shear modulus Available experience and interpretation in other material Intermediate soils (clayey sands to silts) Penetration behaviour Typical results and classification Undrained shear strength Effective stress strength parameters Constrained modulus Small strain shear modulus Coefficient of consolidation General experience Peat/organic silt Underconsolidated clay Chalk Calcareous soils Soil classification Undrained shear strength Relative density Effective stress strength parameters Pile side friction Cemented sands Snow Permafrost and ice Identification of permafrost/ ice layers Special procedures for penetration tests in frozen soil Determination of creep parameters General comment Gas hydrates Residual soils Mine tailings Sawdust and wood choppings Dutch cheese Slurry walls 116

4 vii Volcanic soils Fuel ash Loess soil Lunar soil Examples of unusual behaviour Limiting negative pore pressures due to cavitation Negative pore pressure measurement with filter on the cone Effect of the weight of rig on shallow test results The use of non-standard equipment or procedures Cone size and scale effects Cone penetrometer geometry Length of the cylindrical portion behind the cone included in q c Reduced area behind the cone Non-standard position and area of friction sleeve Cone apex angle Rate of penetration Set-up tests Applying water during penetration Vibratory cone penetrometer Statistical treatment of data Definitions Sources of uncertainty and variability of soil properties Statistical treatment Site investigation strategy and Bayesian updating techniques Recommendation Software application DIRECT APPLICATION OF CPT/CPTU RESULTS Correlations with SPT Deep foundations Axial capacity Factor of safey Settlement Skirt penetration resistance Shallow foundations Bearing capacity Settlement Ground improvement - quality control Liquefaction Liquefaction definitions Application of CPT for liquefaction assessment Cyclic softening Flow liquefaction Minimum undrained shear strength Recommendations for liquefaction evaluation 1 7. ADDITIONAL SENSORS THAT CAN BE INCORPORATED Lateral stress measurements Equipment Typical results Interpretation Cone pressuremeter Equipment Testing procedure Interpretation Seismic measurements Equipment and procedures Typical results and interpretation Electrical resistivity measurements Principles for measurement Equipment and procedures Typical results and interpretation Heat flow measurements Radioisotope measurements Equipment, measurement principles and procedures Typical results Discussion on soil density measured byndt Acoustic noise GEO-ENVIRONMENTAL APPLICATIONS OF PENETRATION TESTING Objectives of a geo-environmental site investigation CPT technology for site characterization Geo-environmental penetrometer logging devices Temperature Electrical resistivity and conductivity Dielectric measurements ph sensors Redox potential Gamma and neutron sensors Laser induced fluorescence Geo-environmental penetrometer sampling devices Liquid samplers Vapour samplers Solid samplers Sealing and decontamination procedures Future trends Summary 203

5 viii 9. EXAMPLES Normally consolidated soft alluvial n, ~, c, ~ na clay, Bothkennar, UK 218 J 9.1 Example profiles Marine, lightly overconsolidated clay, Onsay, Norway Organic clay, lightly overconsolidated, 10. FUTURE TRENDS 223 Lilla Mellosa, Sweden Overconsolidated Yoldia (Aalborg) 10.1 Recent developments 223 clay, Aalborg, Denmark Future developments Overconsolidated clay till, Cowden, UK 208 REFERENCES Sand over silty clay, McDonald's Farm, Vancouver, BC Overconsolidated dense sand, APPENDICES 249 Dunkirk, France 210 APPENDi X A: ISSMFE REFERENCE TEST Normally consolidated very silty clay, PROCEDURE 249 Pentre, UK Worked examples 213 APPENDIX B: SWEDISH STANDARD FOR CONE Loose to medium dense sand, Massey TESTING Tunnel site, Canada 213 APPENDIXC: CALIBRATION CHAMBER Very dense overconsolidated sand, TESTING OF SANDY SOILS Sleipner, North Sea Stiff overconsolidated Gault clay, Madingley, UK 2 INDEX 305