Study On Ground Subsidence Due To Construction Of Metro Tunnel With Un-Pumping Construction Method

Land subsidence, the characteristic of which beng of long duration, in a wide area of influence and hard to take prevention and curation, is an environmental geologic phenomenon which appears as the fall of the elevation of local ground surface. Settlement of ground is mainly induced by exploitation of groundwater, construction of foundation and utilization of underground space.Tunnels in city subway project are constructed in the interior of rockmass. Driving of the tunnel will inevitably disturb the surrounding rock no matter how small the buried depth of the tunnel is. During the process of tunneling, the mechanical equilibrium state of the adjacent formation will change continuously. And also excavation will induce deformation of the adjacent rock towards the free face known as convergence deformation which causes settling of ground simultaneously. On the other hand, disturb of soil and discharge of underwater will induce consolidation settlement of ground as well. The increasing land subsidence will do harm to the building on the ground and the pipeline under the ground unless some measures are taken to restrict it. So, the problem of settlement of ground caused by construction of tunnel in city subway project is always an important research direction.There are two main problem regarding land subsidence that must be solved in this thesis. One is to propose the construction method by which the settlement of ground can be controlled efficiently. The other is to calculate the land subsidence induced by subway tunnel construction.Different construction method brings on different results of land subsidence for metro tunnels which are buried in soft soil with high water level in south of China. The most effective measures to restrict the settlement of ground are reducing disturbance of driving and diminishing the loss of ground water. Drainage method is the most universal techniques in the subway construction with shallow undermining method in our country. This method may provide a favorable condition which may insure the process of subway tunnel construction against water. However, to pump water by wells in drainage method may result in large-area subsidence of ground which may be 70-80 percentage of the total settlement of ground when tunneling in fluent plastic clay formation. Hence, both three dimensional numerical analysis method and centrifuge model test are used to study this problem. Non-drainage method characteristic by controlling the loss of ground water is developed. This method is also verified by the results of practical construction and field monitoring. This thesis adopts the FLAC^3D as compute tool which is a three dimensional...