Numerical model for the zonal disintegration of the rock mass around deep underground workings

• A numerical method is proposed to model the generation and evolution of deep rock zonal disintegration.
• The mechanical damage is modeled through a decrease in the multi-step elastic modulus.
• The element failure criteria are developed based on the maximum tensile stress criterion and strain energy density theory.
• The excavation unloading time directly determines the morphology of zonal disintegration.

Deep underground excavation can produce zonal disintegration in the surrounding rock under certain conditions. This phenomenon has mainly been studied in a qualitative manner using in situ investigations or laboratory experiments. Researchers have also derived analytical solutions, which resulted in the formation conditions for zonal disintegration. However, the analytic solutions developed to date are not suitable for practical engineering applications because of the stringent model requirements and complicated boundary conditions. To investigate the mechanism of zonal disintegration, a numerical method is proposed to model the phenomenon. The following concepts are incorporated into FLAC3D via its built-in FISH. First, coal mine (or tunnel) excavation is considered as a dynamic process. Second, the element failure criteria are developed based on the maximum tensile stress criterion and strain energy density theory. Third, the mechanical damage is modeled through a decrease in the multi-step elastic modulus, i.e., the nonlinear stress–strain behavior is approximated by the multi-linear elastic softening model. Two practical cases with zonal disintegration are simulated using the proposed method. Both simulations predict the same number of fractured zones at the same location as those obtained through in situ monitoring.