Shear band development characteristics in silty soil under coupled confining pressure and strain rate

The shear localisation behaviour of silty soil significantly influences the evolution of engineering hazards such as slope instability. Traditional shear band theory cannot fully quantify the coupling effect of confining pressure and strain rate, limiting its accurate predictive ability for soil failure behaviour. This study uses triaxial shear tests combined with PIVLab technology to investigate the coupled influence of confining pressure and strain rate on the formation, evolution and geometric characteristics of shear bands in silty soil. The results show that increasing confining pressure significantly inhibits soil dilatation, leading to a change in stress-strain response from softening to hardening. Furthermore, the evolution pattern of the shear band changes from a multi-branch/wedge-shaped pattern under low confining pressure to a single concentrated pattern under high confining pressure, exhibiting an ‘aggregation effect’. Increasing strain rate enhances the apparent strength and localisation of the soil by strengthening particle inertia and suppressing structural rearrangement. The classic Perzyna viscoplastic constitutive model is modified by introducing a dynamic yield function that couples confining pressure and strain rate. A nonlinear empirical model capable of accurately predicting the dip angle of the shear band is established, quantifying the influence of confining pressure and strain rate on theoretical reference values.