Numerical simulation of rock behaviour through a discrete model

A common problem of excavation machinery based on mechanical actions is the unknown interaction of the cutting tools with various types of soils. Due to the involved non-linearities, the numerical analysis of such phenomena is very complex. To overcome these drawbacks some authors proposed to model the soil as a collection of spheres. In this paper we apply a strategy for soil modelling which is based on discretization of the soil with rigid disks and suitable contact models. The basic idea is to concentrate at the contact level the real mechanical behaviour of the soil. The goal is achieved by extending the general concept of contact as an unilateral constraint condition, through a suitable constitutive law: the contact laws have been implemented in the node-to-segment contact formulation within the framework of the penalty method. The aim of this work is to study the behaviour of some soils under different loading conditions, and to develop contact constitutive laws suitable for the discrete model. In order to carry out the proposed strategy a "macro" and a "micro" level are established, and macromechanical and micromechanical models are developed. In the micromechanical model the mutual contact interaction between two disks is studied, while the macromechanical model deals with the behaviour of a regular array of disks. The framework for the plastic behaviour of the contact element consists of a failure criterion; a one-dimensional, rate-independent elasto-plastic flow rule for normal and tangential force; two specific yield surfaces, and a hardening or softening law. In this paper we have focused our attention on the simulation of soils and rocks: a new constitutive contact law is developed and applied for the simulation of different soils with different testing conditions (such as uniaxial and shear tests).