A possible prediction method to determine the top concealed karst cave based on displacement monitoring during tunnel construction

The existence of concealed karst caves can cause major displacement and even large deformation of surrounding rock during karst tunnel excavation. As such, these concealed caves pose a large threat to the stability of surrounding rock and represent major hidden threats to safe tunnel construction. Here we report on our investigation of a possible method to predict the top of a concealed karst cave based on displacement monitoring during tunnel construction. Displacement laws of monitoring sections were analyzed and compared to a case study without karst caves after the tunnel was excavated once. Numerical calculation was carried out to verify the proposed method. The impacts of a number of factors were studied by taking into account the effects of displacement fields, such as tunnel depth, the surrounding rock grade, the size of the karst cave, the distance between the tunnel and the karst cave and the depth–span ratio of the karst cave, on the stability of surrounding rock in tunnels. Compared with the case study without karst caves, the surrounding rock deformation affected by the top karst cave during tunnel excavation is discussed, and simulation results were found to be consistent with those predicted by the proposed method. These research results can provide a new concepts for comprehensive forecasting techniques of the concealed karst cave.