A methodology to model slip lines as strong displacement discontinuities within a continuum mechanics context is presented. The loss of hyperbolicity of the IBVP is used as the criterion for switching from a classical continuum description of the constitutive behaviour to a traction-separation model acting at the discontinuity surface. A version of the element-free Galerkin (EFG) method is employed where the slip line is represented as a set of slipped particles. The representation of the slip line as set of cohesive segments promises to remove difficulties in the propagation of the slip line. Two-dimensional examples are studied using the Drucker–Prager material model.