Effect of initial water content on undrained shear behaviour of reconstituted clays

Isotropically consolidated undrained triaxial compression shear tests were performed on three reconstituted clays to investigate the effect of initial water content w(0) on undrained strength behaviour. The values of w(0) were adjusted within the range of 1.0-2.0 times the liquid limit. The predominant clay mineral is identified as illite for the considered clays, based on a semi-quantitative analysis of the X-ray diffraction patterns. The laboratory tests show that the stress-strain curve in terms of deviator stress against axial strain and the effective stress path in terms of deviator stress against effective mean stress are significantly affected by w(0). The undrained strength ratio R-su*, defined as the ratio of the undrained shear strength S-u* to the isotropic consolidation stress, varies with w(0) within a wide spectrum, ranging from 0.28 to 0.60 for the three reconstituted clays investigated. The relationship between void index I-v and S-u* changes with R-su*, and becomes identical to the intrinsic strength line proposed by Chandler when R-su* 0.33. It is also evidenced from the laboratory tests that the value of S-u* depends on both the water content and the liquid limit.