Study Of Land Subsidence Induced By Urban Subway Tunnelling On Complicated Conditions

It is predicted that a great deal of urban metro engineering will be constructed at early-middle period in the 21st century based on flourish metro engineering foreground nowadays, and at one time many geotechnical problems will also come forth. Large land subsidence value induced by metro tunneling can lead to that road surface, buried pipelines and buildings and so on are damaged. Furthermore, bad economic loss and social effect can be brought about. As a result, it is an urgent realistic problem that land subsidence induced by tunneling is forecasted and controlled so as to ensure the safety of close-by building and buried pipeline.As far as complicated geologic condition with weak watery strata, complex construction condition with multi-tunnel system and complex environmental condition with adjacent to building and pipeline are concerned, difficulty and risk of construction are very great and the mechanism of ground settlement and its distribution are also very complex. It is revealed by domestic and overseas data and literatures that research on it is poor, so theoretical study is very weak compared to flourish metro engineering. Relative study in this dissertation is carried out combined with Shen-zhen metro engineering and multi-research techniques are used, on the one hand, so as that results acquired are reliable and reasonable, on the other hand, they can be verified each other and learn from other's strong point offset one's weak point.It is very important that construction process of excavation and support and mechcnical effect of supporting structure are simulated reasonably as far as land subsidence induced by tunneling is forecasted. Thus relative problems are firstly study particularly in this dissertation. To study of land subsidence on complex multi-tunnel system engineering, in virture of nonlinear characteristic of construction routle in underground engineering, mathematical model of optimal excavation sequence aiming to land subsidence is built on basis of dynamic programming theory. Futhermore, control model of contruction effect on land subsidence by tunnelling is also built and construction measure and strategy are also optimized in order to ensure land subsidence by excavation is less than settlement control standard. And then construction processes of complexmulti-tunnel system engineering are simulated by means of 3-D nonlinear FEM and subsidence induced by tunnelling is also study by centrifugal test. Thus land subsidence values and its spatial distribution are forecasted. So as to study of rheology effect of land subsidence induced by tunnelling in soft-weak rock surroundings, 3-D elasto-viscoplastic FE expressions are analyzed and 3-D elasto-viscoplastic FE program is developed and excavation process of subway running tunnel engineering is simulated and space-time distribution of ground settlement is predicted. To study of the effect of groundwater on land subsidence, based on seepage-stress coupling theory, land subsidence distribution induced by tunnelling is analyzed with precipitation or losing water around tunnel cutting face, at one time, VOF (Volume of Fluids) method is used to simulated movement boundary of underground water. To know the effect induced by tunnel excavation on neighborhood pipeline, numerical simulation and centrifugal test are carried out and the safety of pipeline during excavation is predicted by means of given criterion. And the control standard of land subsidence on pipeline is study and its value used as measure object is given out. At one time, the effect induced by tunnelling on building is analyzed.Because results acquired in the dissertation by means of numerical simulation and test are basically consistent with the results by spot measuring, analysis theory and method concerned in the dissertation is reasonable, and prediction before construction is almost right is also proved. Thus theoretical basis and guidance are provided to real engineering, at the same time, a series of key techniques and problems are solved. Valuable design, constructio...