Site Characterization for Cohesive Soil Deposits Using Combined In Situ and Laboratory Testing

The paper presents recommendations for conducting geotechnical site characterizations to obtain design parameters for settlement and stability analyses. It focuses on relatively uniform, saturated cohesive soil deposits with near zero Standard Penetration Test blow counts and soft ground conditions, which means that construction will load the foundation soil beyond its preconsolidation stress. The site characterization program should select an appropriate combination of in situ tests for soil profiling (identify soil types and their relative state) and laboratory tests on undisturbed samples for strength-deformation-flow properties. Although the tools, procedures, and interpretation methods needed to conduct a reliable site characterization program are well developed, general practice often ignores this knowledge. Thus a prime objective of the paper is to provide recommendations for moving practice closer to the state of the art. Components of site characterization covered include site stratigraphy, drilling and undisturbed sampling, in situ testing, and laboratory consolidation and strength testing. Key recommendations include: fixed piston sampling using drilling mud and tubes with an appropriate geometry, piezocone testing for determination of site stratigraphy, radiography of sample tubes, debonding of samples from tubes, evaluation of sample quality, CRS testing to measure consolidation behavior, and anisotropic or K₀ consolidated strength tests to measure undrained shear strength behavior.