This talk presents an implicit solver for non-associative plasticity problems based on the semi-smooth Newton method, using a formulation of a second order cone complementarity problem. The proposed method, derived from the Implicit Standard Material (ISM), is compatible with various spatial discretisation techniques, in particular the Material Point Method (MPM) and the Finite Element Method (FEM). \\[2mm] From footing simulation to slope stability analysis, geomaterials are often described by a nonassociative elasto-plastic model, that are usually simulated with the return mapping algorithm. The goal of this work is to propose an alternative approach, developing a monolithic solver capable of solving the plastic constitutive equation, the potential hardening and the Coulomb friction with unilateral contact, avoiding, in particular, the difficult computation of the consistent tangent operator. Inspired by the ISM framework, the constitutive equations are written as differential inclusion and a semi-smooth Newton method is used to solve the constitutive law within an implicit time scheme. In the first part, the IGM framework is developed, then the spatial discretisation (FEM or MPM) is derived before the non-smooth solver is presented which shows a quadratic convergence, even for large time steps, or load-increments. The method is demonstrated using a footing problem and simulations of complex phenomena such as debris flows or landslide initiation are being developed.