Numerical analysis of stability of underground openings through loading/unloading of in-situ stress fields

By treating the stability of underground openings as a nonlinear system, application of loading/unloading response ratio (LURR) theory is studied, and a new loading/unloading approach is put forward through increase/reduction of in-situ stress fields. Based on the RFPA2D Basic software and physical model tests, a plane strain numerical model is established to study mechanical behavior under multistage loading/unloading, and three response parameters including crown subsidence, horizontal convergence and acoustic emission are studied. The numerical results show that LURRs of these parameters float around 1.0 under not too large load, and the surrounding rocks are stable. With the increase of load, LURRs of crown subsidence and horizontal convergence increase slowly. While the surrounding rocks are close to failure, LURRs present acute fluctuation. It should be noted that LURRs of horizontal convergence at different locations don’t present the same fluctuation amplitude. The acoustic emission doesn’t mean that the distinct change of LURR is close to failure. However, it can indicate the damage evolution of the surrounding rocks. The above-mentioned achievements can be utilized in prediction of progressive instability.