Study On The Stability Of Surrounding Rock Mass With The Tunnels In Xipan & Pantian Expressway

Stability of Surrounding Rock mass with the tunnels is a important research contents. To accurately understand it is the basis of rock engineering design,taking reasonable measures and ensuring safety. There is a mature theoretical system for stability of surrounding rock evaluation, but for the concrete projects, particularly in the western mountainous areas with complex geological conditions, because of the diference of the influencing factors and weight of it, to establish the methods system and analysis the evaluation result must be researched specially.Based on previous research results, the author makes study of the tunnels in Xipan & Pantian expressway. Then analysis the stability of surrounding rock mass with global deformation, and evaluate the infection by faults,level layered structure and structure planes. The final results obtained as below.(1) Geological conditions in the engineering area were investigated, and it is considered that the failure model to be plastic deformation,collapse,flaking and fall-block.(2) Latest findings about rock mass classification are applied to grading the rock mass. On the basis of monitoring data, mechanical parameters are analyzed by the method of inversion.(3) Based on the conceptual model of rock mass structure in the engineering area, Flac3D is used to simulate stress, strain and plastic zone distribution and dynamic characteristics of the rock mass with fundamental theories and methods of rock mass modeling. The excavation sequence and support utility of lining structure are simulated in order to provide basic data and theory for evaluating systematically the stability and supporting designs of the tunnels. The final results obtained as below.①III grade surrounding rock with excellence self-stable ability, and elastic deformation is the main model. It is suitable for constructing with whole section excabation and shotcrete add bolt support.②IV grade surrounding rock with stated self-stable ability, and elastic-plastic deformation is the main model. It is suitable for constructing with whole or step section excabation and shotcrete add bolt,mesh reinforcement and grid steel frame (choice) support.③V grade surrounding rock with bad self-stable ability, and there are elastic-plastic deformation,relaxation deformation,rheological and so on when excavated. Before excavating, It is suitable for advance pre-support and pre-reinforcement. And the construct methods is suitable for whole or step section excabation and shotcrete add bolt,mesh reinforcement and grid steel frame or section steel arch center support.(4) Flac3D,3DEC and Unwedge are used to analysis the structure effect of stability of surrounding rock. Particularly evaluate the infection by faults,level layered structure and structure planes.①Fault rock has obvious impact on the stability of the tunnel, different occurrences of faults and occurring sites have different influence degree in surrounding rock stability of the tunnel. So fault zones should be strengthened in construction.②The stability of horizontal layered rock is determined by its layered structure. Because shearing,sliding,tension of the rock surface are the main factors that can cause the deformation of surrounding rock., it should be strengthened and supported in order to improve the structure of the rock mass.③It is easy to appeared unstable blocks in III and more than III grade surrounding rock , and some IV grade surrounding rock by good integrity of 2～4 structural plane. So we must Predict the blocks according to structural plane characteristics of production, and attention it when constructing.