EFFECT OF THE DAMAGE ZONE AROUND MINING EXCAVATIONS IN ROCK SALT BASED ON INTERNAL STATE VARIABLE TIME-DEPENDENT MODELLING

ABSTRACT: Evaluation of the stress and strain distributions around underground openings in mines of evaporites (rock salt, potash) is essential to determine optimal room and pillar dimensions, minimal distance between levels, and crown pillar thickness. The behavior of such low porosity soft rocks exhibits a strong time- and history-dependency when subjected to deviatoric loading. Observations indicate that the time-dependent inelastic (creep) deformations away from the walls (i.e. inside large pillars) can be ductile, while the rock near the openings often show a semi-brittle behavior with the emergence of a damage zone. This article focuses on the response of the damage zone around mining excavations in rock salt. The analysis is based on the effect of damage, which induces a reduction in stiffness and acceleration of the inelastic strain rate. The numerical investigation evaluates the geometry of the damage zone around underground excavations based on experimental data collected on rock salt. A time-dependent model with a strain-hardening (SH) internal state variable (ISV) and a damage component is used to simulate the response of mining excavations induced by the evolving stress state and related displacements.