Effect of sample disturbance on Gmax of Holocene clay deposits

This paper describes the effect of soil sample disturbance on small strain shear modulus (G(max)) of soft Bangkok clay samples retrieved by using different types of sampling methods and also the other soils from two different sites. Two types of sampling technique were employed, one using fixed piston sampler, driving mechanically at a constant rate (FP) and the other one using floating piston type of samples driven manually (ST). Though the samples were collected at the same site within 5-6 m periphery, ST samples were found continuously lower in stiffness than those of FP series that were closer to in-situ soil stiffness. Reconstituted samples (RC) from the similar soil came to represent the lowermost stiffness boundary. In examining the plot of G(max) against effective vertical stress (sigma(v)'), all of the three sample types (FP, ST and RC) fall in a pretty similar slope at normally consolidated (NC) portion, most of them overlapping. The further YNU series of tests using Ariake clay, Japan and Louiseville clay, Canada confirms the above conclusion referring the negligible effect of sample disturbance on the G(max) behavior at NC state. With the increase in the degree of disturbance, the slope of (log G(max)-log sigma(v)') plot (m) at pre-yield region goes on increasing, reaching ultimately to NC slope at maximum disturbance. The correlation between m and compression coefficients is also drawn from the available data.