Field evaluation of deformation characteristics of a lacustrine clay deposit using seismic piezocone tests

Abstract

The use of the seismic piezocone test (SCPTU) in geotechnical site investigation offers direct field measurement on stratigraphy and soil behaviour. Compared with some traditional investigation methods such as drilling, sampling and field inspecting method or laboratory test procedures, SCPTU can greatly accelerate the field work and hereby reduce corresponding operation cost. This paper presents the methods review to predict the constrained modulus ( M) and to measure small strain shear modulus ( G max) from SCPTU data. The capacity of current interpretation methods to predict the constrained modulus ( M) was evaluated for Lixia River lagoonal soils. Several sites in Lixia River area were selected for this study. In each site, SCPTU tests were performed and the soundings of cone tip resistance ( q c), sleeve friction ( f s), pore pressure ( u 2), and shear wave velocity ( V s ) were recorded. The predicted M values obtained from the SCPTU interpretation methods were compared with the reference values determined from the laboratory consolidation tests. Results of this study showed that the Sanglerat method was able to predict M better than the other methods. Two new correlations were also developed to predict M from the corrected cone tip resistance ( q t) and the net cone tip resistance ( q n). Small strain shear stiffness can be tentatively estimated in the absence of direct measurement of shear wave velocity. The reliable result was obtained using an association between G max, q t and pore pressure parameter B q . Compared to field downhole wave velocity measurements, SCPTU can lead to a more reliable measurement of maximum stiffness profile with depth. The stress–strain–strength response of the clays was evaluated by the maximum shear stiffness and undrained shear strength.