The room-and-pillar excavation method is extensively used in the salt rock mining industry due to the inherent stability of salt rock. This example illustrates the practical use of PLAXIS 3D for the preliminary assessment of stability and time-dependent deformation in salt rock under square room-and-pillar mining conditions. In this example, a 3D model representing half the width of a vertical layer of the mine is constructed to simulate the entire mine, utilizing symmetry to save computing time.

Salt rock exhibits time-dependent deformation (creep) behavior, which can lead to stability issues when excavated deep underground. Therefore, this must be considered in stability analysis for salt mine design. To model this creep behavior, the Norton double power creep law with Mohr-Coulomb and Tension cut-off failure criteria (N2PC-MCT) is used in this exercise to simulate the time-dependent deformation and predict potential failure and damage of the salt rock structures. The strength factor is used to evaluate the stability conditions of the room and pillar structure in this exercise.