UNDRAINED BEHAVIOUR OF OVERCONSOLIDATED SATURATED CLAYS DURING SHEAR

Abstract

A laboratory investigation is made on the undrained behaviour of two heavily overconsolidated saturated clays during shear. The effect of heavy overconsolidation on undrained behaviour of saturated clays is markedly different as compared to that for low degree of overconsolidation and it is function of clay type. The strength envelope is highly nonlinear for heavily overconsolidated clays at low stress levels. Increase of q_f/σ_c' is much pronounced at high overconsolidation rations. The pore water pressure parameter A at failure is very much dependent on the type of clay and the stress system used. For the first time development of shear stress, pore water pressure with strain and OCR is discussed. The pore water pressure parameter A increasing with strain at low OCR values converges to a low strain-independent value at a critical OCR value for each clay and then decreases with strain for high OCR values leading to a steady, strain-independent, A value. Tangent modulus values are given as a function of OCR and confining pressure for use in analysis of foundation engineering problems in the clay deposits under undrained condition. The investigation provides valuable information in the much needed high OCR range of low stress levels where very little data is available.