Limit Analysis Of The Scope Of Collapse For Tunnel Constructed In Rock

Collapse is the most common disaster in tunnel constructions. It causes not only project delays, loss of property, but also casualties. So it’s very practically significant to reduce the occurrence of collapses, propose some reasonable and targeted advices of the collapse, determine the tunnel support pressure and study on the stability of surrounding rock through the research of the development and the scope of the collapse.According to former studies of other researchers, this thesis divided the tunnel collapse into3modes:local landslides, arched landslides and penetrated landslides. And we chose the last two modes, whose collapse surface is symmetrical to the y axis to research the scope of collapse associated with H-B criterion based on the Greenberg extremum principles, the variational methods and the theory of limit analysis. And then, the results derived were studied to analysis the influence of different value of the parameters to the shape of the collapse surface. And the rationality and practicability of the results were verified through the comparison of the heights of collapse block derived by the results in this thesis and the empirical formula in the Railway tunnel specifications respectively.The main achievements of this thesis are:(1) We made a brief introduction of Greenberg extremum principles, and made some transformation. We got the principles in the forms of rates.(2) We derived the solutions of the collapsing shape for rectangular and circular section tunnel with penetrated and arched landslides respectively, and got a parse expressions and three equations.(3) We transformed the solution into one associated with M-C criterion according to the connection between the H-B criterion and M-C criterion. After the comparison with the result that H. Lippmann made in1971, we proved the correctness of the theory(4) We derived the height of the collapse according to the result of the arched collapse of the rectangular section tunnel. And the rationality and practicability of the results were verified through the comparison of the heights of collapse block derived by the results in this thesis and the data in the Railway tunnel specifications respectively.