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 w0on undrained strength behaviour. The values of w0were 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 w0. The undrained strength ratio R*su, defined as the ratio of the undrained shear strength S*uto the isotropic consolidation stress, varies with w0within a wide spectrum, ranging from 0·28 to 0·60 for the three reconstituted clays investigated. The relationship between void index Ivand S*uchanges 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*udepends on both the water content and the liquid limit.