Effect of OCR on sampling disturbance of cohesive soils and evaluation of laboratory reconsolidation procedures

Abstract

The paper presents the results of an experimental investigation of sampling disturbance in cohesive soils through single-element triaxial tests on resedimented Boston blue clay (RBBC). The first part of the paper discusses the effect of the overconsolidation ratio (OCR) (1–8) of the soil on postdisturbance compression and undrained shear behavior. The results demonstrate that sensitivity to disturbance decreases markedly with OCR. It is also found that for the medium-sensitivity soil tested, the estimate of the preconsolidation pressure is not significantly affected by OCR. The second part of the paper discusses laboratory reconsolidation procedures. For OCR1 RBBC, the recompression method is not effective in recovering the stress–strain behavior of the soil and, for greater disturbance, provides an increasingly unsafe estimate of the strength. For OCR4, provided the reconsolidation path reproduces the path that occurred in the field, this procedure succeeds in recovering the intact stress–strain–strength behavior of the soil. SHANSEP reconsolidation was investigated for normally consolidated RBBC only. For modest levels of disturbance, this is an effective means of evaluating both the stress–strain and the strength behavior of the soil. For greater levels of disturbance, the stress–strain behavior is not fully recovered, but the method continues to provide conservative estimates of the undrained strength.Key words: sampling disturbance, clays, overconsolidation ratio, undrained strength, recompression, SHANSEP.