Study On Failure And Criteria Of Tunnel Structure

The surrounding rock is destroyed by repeated geological act, and the destroyed rock masses are disturbed or destroyed another time, the rule of destruction is different from that of complete material. The rule of destruction and deformation is controlled by the structure of rock mass, and the deformation and destruction of rock mass cannot be decided by the criteria of general materials. At present, the difficulty of the study of tunnel include five factors, first, the unclear model, second, the indistinct criteria, third, all of the problem that we are facing being limited information, the forth, limited knowing of destruction mechanism, the fifth, much indefinites.At the moment, the basic theory of loading mechanics is always used to search the problem of rock mass failure, but unloading and loading have different stress road and different destruction effect, so there are much difference in destruction mechanics and deformation between unloading and loading mechanics, if loading mechanics is used to study the destruction property of tunnel excavation and its stability, the result which agree to real engineering cannot be obtained. The comparison of loading mechanics and unloading mechanics shows that the unloading mechanics is more close to real engineering.The paper uses catastrophe theory to construct the models of the key supporting rock mass that made of different kinds of rock, and discusses the critical requirement of fail. On the critical condition, if the system has small disturbance, the whole stable system will fail. On stable condition, strong disturbance can make the system fail ahead of time. Combining gray theory and catastrophe theory, the gray energy catastrophe model is brought out according to the critical value of energy. The real example shows that the critical value is unique. The analytical process of rock mass fail shows that the process of fail of the rock mass is the process that dissipation structure is formed, and that self-organization of surrounding rock is built during the process. The phenomena of bifurcation and chaos emerge during the process of development of surrounding rock system. The analysis of buckle theory shows that the result of elastic-buckle is much bigger than that of non-line buckle. The result of non-line buckle is close to the real engineering. When there is original stage support only, the load ratio of surrounding rock gets more and more bigger with the increasing of crust stress, correspondingly, the load ratio of initial stage support gets smaller. When the initial stage support and the second support act each other,the load ratio of surrounding rock is more than fifty percent, and it has little change with the increasing of crust stress. The whole analysis of the surrounding rock and support shows that the bottom arch of liner and the feet of liner have serious stress concentration, so do the sidewalls and the foot of a wall of the surrounding rock. The criteria of the permissive limit displacement and the changing ratio of displacement are studied to judge stability of whole analysis of surrounding rock and liner, so do the acceleration of displacement and speed ratio of deformation. For the real engineering, all the criteria are relative in quantity. Generally, synthetical judgment is utilized to distinguish the stability of the tunnel.