Mechanism And Safety Thickness Prediction Of Water Inrush For Overlying Water-filling Karst Cave In Tunnels And Engineering Applications

With great development of tunnels and underground engineerings, karst disasters are gradually important. The water inrush of karst cave with water is one of the morst serious geological disasterts during the construction of tunnels. Water inrush can easily make the construction period extended, instruments destructed and casually increased. For the facts mentioned above, the methods of theoretical analysis, numerical calculation and software design are accepted to analyze the minimum safety thickness between karst cave and tunnel. These analysis is supposed to provide favorable application value for tunnel construction. The main contents are as follows:(1) The occurrence regularity of karst cave and disaster-pregnant mode are summarized. Based on the existing related literature summary and analysis, the geological occurrence regularity of karst cave with water and water filling rule are summed up. By the factor summary of capacity of water inrush and destruction channel, a preliminary analysis of the disaster-pregnant mode have been accomplished. The destructive force of karst cave with water is often attached with its capacity of water inrush and the formation of destruction channel. Based on the failure mode of karst cave with water, the disaster-pregnant identification is summarized from the foreboding information of geology, mechanics and geophysical field.(2) A three dimensional numerical model of tunnel with water-filling karst cave is establish, and the criterion of minimum safety thickness between karst cave and tunnel is initially proposed. With the large-scale numerical calculation software Ansys 10.0, a three dimensional numerical model of tunnel with water-filling karst cave is establish. A series of physical and mechanical parameters are set to form a multi-level calculation cycle. The seepage model of FLAC3D is used for convergence calculation of tunnel excavation. Through the numerical simulation, the mechanics information of tunnel surrounding rock, under the condition of karst cave with water, can be revealed. Also, the the minimum safety thickness between karst cave and tunnel can be obtained.(3) A software system of prediction for the minimum safety thickness based on the results of numerical calculation is designed. The Microsoft Visual C++ platform is used to design a software system including the prediction of the minimum safety thickness and water inrush warning. Based on the results of numerical calculation, simple regression and multiple regression are accepted to establish the prediction mathematical model of the minimum safety thickness between karst cave and tunnel. Furthermore, the evaluation for level of surrounding rock has its own module. The level of surrounding rock is conducted by the Analytic Hierarchy Process and the expert scoring principle, which comprehensively considers the subjectivity and objectivity. Two engineering cases are applied in the software system, and the results have high consistency by comparing with the excavation.