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Recommended Practice for Soft Ground Site Characterization: Arthur Casagrande Lecture

A soft ground condition exists whenever construction loads a cohesive foundation soil beyond its preconsolidation stress, as often occurs with saturated clays and silts having SPT blow counts that are near zero. The paper recommends testing programs, testing methods and data interpretation techniques for developing design parameters for settlement and stability analyses. It hopes to move the state-of-practice closer to the state-of-the-art and thus is intended for geotechnical practitioners and teachers rather than researchers. Components of site characterization covered include site stratigraphy. | Recommended Practice for Soft Ground Site Characterization Arthur Casagrande Lecture Práctica Recomendada para la Caracterización de Sitios en Terreno Blando Conferencia Arthur Casagrande by Charles C. Ladd Hon. M. ASCE Edmund K. Turner Professor Emeritus Department of Civil and Environmental Engineering Massachusetts Institute of Technology Cambridge MA USA ccladd@mit.edu and Don J. DeGroot M. ASCE Associate Professor Department of Civil and Environmental Engineering University of Massachusetts Amherst Amherst MA USA degroot@ecs.umass.edu prepared for 12th Panamerican Conference on Soil Mechanics and Geotechnical Engineering Massachusetts Institute of Technology Cambridge MA USA June 22 - 25 2003 April 10 2003 Revised May 9 2004 Table of Contents List of Tables.iii List of Figures.iv ABSTRACT.1 1. INTRODUCTION.2 2. GENERAL METHODOLOGY.4 3. SOIL STRATIGRAPHY SOIL CLASSIFICATION AND GROUND WATER CONDITIONS.5 4. UNDISTURBED SAMPLING SAMPLE DISTURBANCE.6 4.1 Sources of Disturbance and Procedures to Minimize.6 4.2 Radiography.10 4.3 Assessing Sample Quality.10 5. IN SITU TESTING.14 5.1 Field Vane Test.14 5.2 Piezocone Test.16 5.3 Principal Recommendations.22 6. LABORATORY CONSOLIDATION TESTING. 23 6.1 Fundamentals.23 6.2 Compression Curves.24 6.3 Flow Characteristics.27 6.4 Principal Recommendations.27 7. UNDRAINED SHEAR BEHAVIOR AND STABILITY ANALYSES.29 7.1 Review of Behavioral Fundamentals.29 7.2 Problems with Conventional UUC and CIUC Tests.34 7.3 Strength Testing for Undrained Stability Analyses.35 7.4 Three Dimensional End Effects.39 7.5 Principal Recommendations.39 8. LABORATORY CONSOLIDATED-UNDRAINED SHEAR TESTING.40 8.1 Experimental Capabilities and Testing Procedures.40 8.2 Reconsolidation Procedure.42 8.3 Interpretation of Strength Data.46 8.4 Principal Recommendations.50 9. SUMMARY AND CONCLUSIONS . 51 10. ACKNOWLEDGMENTS.52 REFERENCES.53 ii List of Tables Table 1.1 Clay Properties for Soft Ground Construction.3 Table 2.2 Pros and Cons of In Situ vs. .