ORIENTATION OF SHEAR BANDS IN FRICTIONAL SOILS

The elastoplastic Mohr-Coulomb (MC) model is shown to overestimate the inclination of shear bands in granular materials. An extended Mohr-Coulomb (EMC) model is proposed to get a more accurate analytical expression for the average orientation of shear bands in soils. The EMC model uses an additional plastic mechanism that softens the transverse modulus and promotes strain localization similar to the vertexlike model of Rudnicki and Rice. Its mathematical structure is simple enough to derive analytical expressions for the plastic modulus and shear-band orientation at the onset of strain localization. The paper also introduces the concept of postcritical localization to account for the scattering of experimental data on the orientation of shear bands in soils. The concept of delayed localization and the EMC model allows us to retrieve the conservative lower and upper bounds of Roscoe and Mohr-Coulomb and to determine more accurate bounds for the average orientation of shear bands in frictional soils.