Tunnel Through The Inclined Rock Sand And Gravel Numerical Analysis Of The Construction Process

Rail transit system has entered a period of rapid development in China, the subway that large capacity, fast punctuality, comfort, safety, save land, reduce pollution and so on to the day-to-day travel, living and lifestyle have brought many benefits, quickly becomes a modern urban transport. With the subway tunnel construction in full swing, a variety of complex geological problems, such as crossing the cave, high strength of granite, the muddy soil with high water table and a large amount of water, the sand and gravel layer and so on, become one of the problems to be solved by people. Sand and gravel layer structure that is loose and uneven distribution has strong discrete features. Now, people use the shield law and mining method excavation to research diagonally across the flat or all throught geological structure of the sand and gravel layer tunnel,but oblique this geological conditions study is not ripe, uneven ready Experiences. Based on a subway tunnel engineering example, rock stability, forepolling measures, shallow excavation methods and the collapse reasons diagonally across the sand and gravel layer tunnel are studied by using the finite element software.First, the theory and method used is expounded, such as the constitutive relation of the surrounding rock material and advanced small pipe, just arching, bolt and shotcrete mechanism of action and the construction points. Then the three-dimensional numerical model of the subway tunnel through the sand and gravel layer is builded. Just arching and bolt structure use elastic material simulation, advanced small pipe, surrounding rock, shotcrete structure use D-P materials simulation and boundary conditions constraint by boundary displacements. Using full-face method simulate the tunnel in the presence or absence of advanced small pipe and have the advanced small pipe role, whether the anchor existence of the two conditions excavation and using step method simulats tunnel excavation process. Tunnel surrounding rock displacement field, stressfield, variation of the plastic zone and the supporting force variation are comparatived. A variety of simulated conditions during tunnel excavation, the tunnel diagonally across the sand and gravel layer of the collapse reasons are analysed.Through this study knows that the advanced small pipe can effectively control the stress and plastic zone of surrounding rock and plays an important role during tunnel excavation. The bolt that length of3.5m reinforcement is analysed and the results show that the stress of tunnel surrounding rock is smaller than no bolt case stress, but it change little. In addition, the results of the full-face method excavation and the step method excavation is comparative. It can be seen that the stress of the surrounding rock caused by the application of full-face method excavation is smaller than step method excavation. In this case full-face method excavation is recommended. It not only can reduce the disturbance to the surrounding rock but also improve construction speed. Advanced small pipe and the initial shotcrete can effectively reduce the displacement of the tunnel arch and the larger displacement resaults in the thickest part of the sand and gravel layer.The plastic zone first appears in the sand and gravel layer and weak weathered rock, which is due to the two relatively large difference stiffness. The tunnel collapse mainly due to loose sand and gravel layer structure, uneven distribution, overall strength and low cohesion.