The Theoretical And Methodical Research On Surface Settlement And Pipeline Deformation Due To Construction Disturbance In Metro Tunnel Construction

With the development of municipal construction, construction disturbances have more and more influences on the environment. This paper takes as a topic: the influence of surface settlement and pipeline deformation due to construction disturbance in Metro tunneling and as the background of Beijing Metro construction. That makes emphasis on the regularity of surface settlement and deformation in spite of many factors on surface settlement. The studies have focus on two important factors: stress state and water content and the both of them have effects on soil properties. We attempt to have shown the reason of layer losses and surface settlement due to tunneling construction.Firstly, the author has researches on basic engineering properties of soil layers in tunneling construction, especially in the relationship between the changes of matric suction (negative pore water pressure) and soil strength data. The results have obviously shown on the control of soil strength to matric suction in the different suction. According to unsaturated soil strength theory presented by Fredlund, we have taken lead in establishing a formula of soil strength in Beijing area's layers taking into consideration matric suction and the relationship between water content and matric suction. The change of water content is also a kind of disturbance from board angles. We still lack in systematic researches of its regularity although ones have recognized that the changes of water content have effects on soil strength. This paper studies the change pattern of soil strength in the different water content as an example of silty clay soil in Beijing area. The results have shown that the changes of water content in the scope of 10-20% have greatly influences on soil strength. So in the project design, it is necessary to give actual watei content in the computation of soil strength value. This paper discussed about the changes of stress state on effect of soil properties. The reason of surface settlement and layer losses is that the stress state is not primeval one in and after tunneling construction. Therefore it is necessary to select strength data in actual stress path in making tunnel deformation and stability analysis with continuous media mechanics. The testing and analysis have shown the tunneling construction disturbance makes the soil strength change and tends to be lower in all. Thus, we should take into fully consideration construction disturbance influences on soil strength in real project practice. Surface settlement is due to layer losses and the layer losses are due to the changes ofstress state and water content. It is necessary to probe into the principle, but to pay more attention to the aftermath of layer losses - surface settlement and its regularity. This paper has focused on discussing about the regularity of surface settlement in tunneling construction. Tunneling construction is divided into two methods: shielding and mining. The empirical formula of curve of surface settlement and the settlement scope are given respectively in term of theoretical analysis and measurement results. The conclusion is of great significant in design and construction in Beijing metro. In tunneling construction, the changes of stress state and water content lead to surface settlement and it causes the deformation of ground pipeline. It is difficult to measure it. This topic makes attempt to make spatial relationship between tunnel construction and pipeline through surface settlement to control pipeline deformation indirectly, that is, surface deformation value is deducted reverse by allowable deformation value. That means that we take maximum settlement value as an objective value, that is, to control surface settlement is to control pipeline deformation. Its research paths are to make decision of computational method of maximum surface settlement and settlement pattern firstly; then to establish the relationship between maximum surface settlement and ground pipeline deformation and strain, to get maximum surface settlement in term of th...