Tunnel Spray Anchor Retaining Structure Load Mechanism And Applied Research

Cross-harbour tunnel does not occupation of land, does not hinder the navigation, does not affect the ecological environment, is one kind of extremely safe all-weather channel. At present, the world has been completed and planned for the construction of cross-harbour tunnel has 20 multi-strip, are mainly located in Japan, the United States, Western Europe, Kowloon of Hong Kong. In recent years, with the rapid development of economic and construction technique, China have the ability to build cross -harbour tunnel. At present in China, there are xiang'an in Xiamen and Jiaozhou Bay in tsingdao cross-harbour tunnel under construction.This article is in the background of the surrounding rock with grades IV in a cross-harbour tunnel, the main contents and conclusions are:(1) With finite element method software ABAQUS, a 3D elasto-plastic finite element model is established, the interaction between concrete lining, bolt and surrounding rock are considered, the time effect of rock excavation are considered. It is concluded that the stresses focus on the the arch lumbus, arch feet, the shear failure is easy to take place at these areas, we must take enough attention during construction. The displacement at arch vault, arch bottom are larger, and it is prone to collapse, and need support timely after excavation. It can be considered to build inverted arch in order to limit the vertical displacement at arch bottom. There is plastic zone at arch lumbus, resulting in the surrounding rock here has lost stability, and it's prone to collapse. There is stresses focus on the the arch lumbus of lining, and it's easily subjected to plastic failure. Most bolts under tensile stress(only a little under compressive stress), the maximum stress nearly 70 MPa. The safety factor of shotcrete linning and rock bolts meet the requirements.(2) By changing the support parameter(bolts length, bolts interval and coefficient of load releasing), It is concluded that by changing bolts length have slight effects on the surrounding rock stress, surrounding rock displacement and plastic zone of surrounding rock. Changing bolts interval have slight effects on the surrounding rock stress, but decreasing bolts interval can reduce the horizontal displacement of the arch lumbar and plastic zone of surrounding rock. Increasing the coefficient of load releasing can reduce some surrounding rock. However, some displacement and plastic zone of surrounding rock has increased. Increasing the bolts length, decreasing the bolts interval as well as increasing the coefficient of load releasing will reduce lining stress and bolts axial tensile stress. (3) By using strength reduction technique, analysis for safety coefficient of stability of surrounding rock with primary shotcrete lining and rock bolts under the four limit state criteria, Including divergence of the computation, displacement of characteristic points, the running-through of the plastic zone of the surrounding rock and the running-through of the plastic zone of the shotcrete and a great amount of rock bolts yielding. It is concluded that the apperance of divergence of the computation may precede by displacement of characteristic points, the rapid increase displacement of characteristic points are not significantly, it is can be considered the safety coefficient of them are the same. The safety coefficient of the running-through of the plastic zone of the surrounding rock and the running-through of the plastic zone of the shotcrete and a great amount of rock bolts yielding are less than the divergence of the computation and displacement of characteristic points. Therefore, the plastic zone is a necessary condition for the destruction, but not sufficient condition. We should also consider whether it has unlimited development of plastic deformation. For the criterion of divergence of the computation and displacement of characteristic points, changing bolts lenght and interval have slight effects on them. For the criterion of the running-through of the plastic zone of the surrounding rock, increasing the bolts length can increase the safety coefficient, but changing bolts interval has slight effects on it. For the criterion of the running-through of the plastic zone of the shotcrete and a great amount of rock bolts yielding, increasing the bolts length and decreasing the bolts interval both can increase the safety coefficient.