Sample Disturbance Effects in Silt

Abstract

This paper presents results of testing good-quality piston tube samples and parallel block samples from three silt sites in Ireland and Norway. Theoretical work and laboratory strain damage tests suggest that good-quality tube samples can be obtained provided the sampling process remains undrained and the tubes have a sharp cutting edge. Laboratory tests confirm that at two of the sites the piston tube samples are effectively equivalent to the block samples. However, at the third site densification of the piston tube samples occurred and the laboratory tests produced nonconservative design parameters. Given the uncertainties of the effects of piston tube sampling of the silts, it seems prudent to assess likely disturbance effects using parallel in situ tests, for example piezocone penetration testing (CPTU) or shear wave velocity testing. The CPTU pore pressure data can be used to assess the degree of drainage which is likely to have occurred during sampling, and shear wave velocity can be used to assess possible densification.