Suction Measurements as Indicators of Sample Quality in Soft Clay

Soil samples removed from the ground during sampling possess a suction in their unconfined state. This suction may vary depending on the degree of disturbance induced during the sampling process. The objective of this work is to examine the feasibility of using suction measurements for sample quality assessment. A number of suction measuring techniques are reviewed and examined on samples of varying quality from two well-characterized soft clay sites, Onsøy in Norway and Ballinasloe in Ireland. Most of the techniques tested gave comparable results, although the cell pressure loading method provided the most variable measurements. The Japanese and University of Massachusetts Amherst suction probe techniques provide relatively quick and consistent suction measurements, requiring less than half an hour to stabilize. In terms of sample quality the Sherbrooke block samples consistently exhibit higher suctions than the 76 mm, 54 mm, and continuous soil samplers for the Onsøy test site. Suctions measured on the Japanese 75 mm samples are similar to those measured on the block samples. The 5° displacement sampler provides the highest suctions on the Ballinasloe samples. It is observed that the quality of samples indicated by suction measurements is similar to that inferred from the normalized change in void ratio (Δe/e₀) criterion.