Mechanics Response Anslysis Of Surrounding Rock On Weak Rock Station Tunnel With Large Span

Design and construction of large span tunnel are perfect day by day along with the development of the transportation business. But still keep existing some problems.Some general construction methods, such as full face method or partial excavation method, are not safe enaugh for excavating entrance segment of long span tunnel. So some reasonable construction methods are needed. They can be selected by experience and particular engineer geology condition. And then decide how much area of every partical excavation face, the distance of every bench, and deside withch additional auxiliary methods are also needed.Especially along with the construction of long span station tunnel, the mode of stress history and distributing, dynamic prediction of relaxation dimension of surrounding rock, and evolutionary process of plastic, zone etc., are not researched and generalized by other study currently. But they are very important for design and safe construction of long span station tunnel, so they are the problems need to be resolved immediately.The paper mainly relys on the three lanes long span and station tunnel of He Luo mountain on Da Li railway from Da Li to Li Jiang. The cross section area of the tunnel is more than 240 square meters. The paper represents some general construction methods of long span tunnel which are mostly used currently. A 3-D model of the tunnel is established with ANSYS. And numerical simulation is carried out by FEM. Along with the field monitor and measureation, the mode of stress history and distributing, evolutionary process of plastic zone, and the evolutionary process of displacement of surrounding rock are mainly studied under the construction of bench excavation. In addition, the appropriate distance of every bench is analysis and generalized. Some conclusion is in follow. The construction of bench excavation with appropriate distance of every bench is feasible in construction of long span station tunnel in weak rock. It can control the deformation, stress distributing, plastic zone of surrounding rock effectively. The mode of stress history and distributing characteristic and evolutionary process of plastic zone are generalized. Longitudinal influence scope of excavation of every bench is presented. The appropriate distance of bench is about 0.5B-0.8B(B- the span of tunnel). There will be some certain reference meaning to similar engineering with above mentioned conclusion.In addition, centrifugal test and numerical simulation are verified each other by the comparision of their results..