Main Factors Governing Residual Effective Stress for Cohesive Soils Sampled by Tube Sampling

Abstract

The residual effective stress (p'r) was measured for various clayey soils collected from various parts of the world, including Japan. All samples studied in this paper were retrieved by the same sampling method, i.e., using the Japanese standard sampler. However, measured p'r/σ'vo, where σ'vo is the in situ effective overburden pressure, considerably varied for different sites as well as with depth. This paper examines main factors governing the p'r value, focusing on location of the sample in the sampling tube; transportation of the soil samples; time duration between retrieval of the sample and extrusion of the sample from the sampling tube; overconsolidation ratio (OCR); clay content and plasticity index (Ip). In addition, the p'r values are correlated to the volume change generated when the in situ σ'vo is applied in the oedometer test, which is extensively used for assessment of the sample quality. The largest measured value of p'r was found at one third of the sample length from the cutting edge of the sampling tube. The effects of the transportation and the time duration from the sampling to the extrusion of the sample are not prominent for the p'r value. Any clear relations between p'r and Δe/eo are not found, where Δe and eo are the void ratio change caused by applying σ'vo and the initial void ratio, respectively. Among factors examined in this paper, OCR is the most effective factor: i.e., as OCR increases, p'r/σ'vo ratio increases for every studied site. However, when compared at different sites, the p'r/σ'vo ratio at the same OCR is considerably different. In spite of some exceptions, there exists a tendency that p'r/σ'vo ratio increases with the increase in the clay content as well as Ip.