Initial simulations of empty room collapse and reconsolidation at the waste isolation pilot plant

Room ceilings and walls at the Waste Isolation Pilot Plant tend to collapse over time, causing rubble piles on floors of empty rooms. The surrounding rock formation will gradually compact these rubble piles until they eventually become solid salt, but the length of time for a rubble pile to reach a certain porosity and permeability is unknown. This paper details the initial model development to predict the porosity and fluid flow network of a closing empty room. Conventional geomechanical numerical methods would struggle to model empty room collapse and rubble pile consolidation, so three different meshless methods, the Immersed Isogeometric Analysis (IGA) Meshfree Method, Reproducing Kernel Particle Method (RKPM), and Conformal Reproducing Kernel (CRK) method, were assessed. First, each meshless method simulated gradual room closure, without ceiling or wall collapse. All methods produced equivalent predictions to a finite element method reference solution, with comparable computational speed. Second, the Immersed IGA Meshfree method and RKPM simulated two-dimensional empty room collapse and rubble pile consolidation. Both methods successfully simulated large viscoplastic deformations, fracture, and rubble pile rearrangement to produce qualitatively realistic results. Finally, the meshless simulation results helped identify a mechanism for empty room closure that had been previously overlooked.