Mechanism And Control Measures Of Collapse Of Mountain Tunnel

Collapse frequently occurres in the construction of mountain tunnel, which leads to great economic loss and heavy casualties. With the rapid development of the economy and construction of expressways, the cost of collapse treatment increases year by year. It has great realistic significance to do research on the mechanism and control measures of collapse of mountain tunnel.By means of numerical simulation and theoretical analysis, combining with geological survey and in-site monitoring, the mechanism and prevention measures of tunnel collapse were studied, and a method of collapse prediction was explored. The sensitivity of influence factors of tunnel collapse was studied by analytical hierarchy process. The pressure-arch theory of collapse scope was studied and pressure-arches in various stress fields were analyzed. New effective methods of surrounding rock classification and a early-warning model of instability risk were put forward. Here, the influence of fault fracture zone on surrounding rock stability and optimized treatment schemes of collapse in such a zone were researched. At the same time, the mechanical rules of double-lining in creeping surrounding rock were studied. Meanwhile, the mechanism and prevention measures of collapse at tunnel exit were analyzed. Based on catastrophe theory, the influence of rainfall on collapse which occurred in shallow tunnel was discussed in the thesis. A method was put forward to evaluate the safety and stability of lining at tunnel exit, and a method of time and space prediction of collapse in loose wall rock of tunnel exit was proposed. Finally. the main results and new ideas of this study are as follows:(1) The main factors of collapse are analyzed. The conclusion is presented that the properties of surrounding rock and groundwater are the most important influence factors of collapse. Tunnel collapses are systemically classified according to the occurrence position.(2) Based on the pressure-arch theory, pressure-arch lines in different stress fields are computed. The research shows that pressure-arches in different stress fields are different. which is related to judge criterion. Considering the engineering safety. the judge criterion that the minimum principal stress is tensile stress should be selected to analyze pressure-arch.(3) Based on the delphi-ideal point method and set pair analysis, new surrounding rock classification models are established, which can provide evidence for evaluating the risk of tunnel collapse. An efficacy coefficient method is applied to evaluate the stability of surrounding rock, and an early-warning model of instability risk for tunnel surrounding rock is established.(4) Optimized construction scheme of tunnel collapse in fault fracture zone is presented. Based on viscoelastic infinite element theory, the rules of double-lining in creeping surrounding rock are studied, which can provide experiences and references for lining design in fault fracture zone.(5) Collapse at tunnel exit is caused by instability of tunnel face and loose rock together with soil mass collapse at tunnel roof. The primary support should be constructed timely and advanced support is necessary. Cusp-catastrophic models of shallow tunnel under rainfall action are established. The instability criterions are derived when surrounding rock is combined with different rock and soil mass. A method is presented to evaluate the working state of lining at tunnel exit.(6) A new model which is used to predict the occurrence time and position of collapse is established. Based on stress-transferring theory, the instability criterion and critical distance in loose wall rock of tunnel exit when collapse occures are derived. Based on the grey theory and synergetic theory, occurrence time of collapse can be predicted. The prediction model is highly accurate which has been proved by a practical project.