COUPLING EFFECTS OF INITIAL SHEAR STRESS AND LOADING RATE ON STRENGTH BEHAVIORS OF SATURATED SOFT CLAY

Undrained triaxial compressive tests are carried out on Hangzhou saturated soft clay to investigate the coupling effects of initial shear stress and loading rate on the monotonic characteristics of soft clay. It is observed that the shear strength decreases and the total strength increases as the initial shear stress increases. When the initial shear stress is 60 kPa,the shear strength decreases about 60%. The pore water pressure decreases with the increase of initial shear stress. When the initial shear stress is 60 kPa,the pore water pressure reduces about 50%. As the increase of loading rate,the strength increases and pore water pressure decreases. The stress-stain curve shows the strain-hardening characteristic without initial shear stress. However,it turns to be strain-softening with the increase of initial shear stress. Empirical equations for the peak strength and pore water pressure considering the coupling effects of initial shear stress and loading rate are proposed respectively by introducing the normalized peak shear stress parameter s and pore water pressure parameter ΔP . It is observed that with the increase ofnormalized strain rate,s increases and ΔP decreases. The relationships between s, ΔP and normalized strain rate show linearity with a semi-log scale. In such a case,the effect of initial shear stress on s and ΔP is not significant.