Shear Strength Behaviour of Overconsolidated Clays

Abstract

It is generally understood that there exists a hysteresis loop between the normally consolidated and overconsolidated effective stress Mohr-Coulomb-failure envelopes, the size of hysteresis loop being a function of the past maximum consolidation pressure. Research findings of different investigators in this regard are at variance. This paper presents the results of an experimental investigation on two remoulded clays in CIU compression tests, varying both maximum past consolidation pressure and the overconsolidation ratio. Test data is analysed in terms of Mohr-Coulomb as well as Hvorslev failure envelopes. Test results show that the effective stress Mohr-Coulomb failure envelopes are uniquely defined independent of overconsolidation ratio, past maximum pressure and the failure condition such as the peak deviator stress, peak effective principal stress ratio and the peak porewater pressure. When the failure is denfined at a strain level lower than that of the peak stress condition, unique effective stress parameters ( c ' and ϕ ') equal to the peak stress values are observed at pre-peak strains (ε ≃ 6 percent) even bofore the peak stress conditions are reached (ε a ≃ 15 percent). From the view point of Hvorslev criterion, the shear strength of the two remoulded soils is essentially through ϕ e ' and it is independent of maximum past pressure.