| At present, with the rapid growth of the population in the world, shortage of land resources is more and more. With the quickening pace of urbanization in China, the land resource is becoming more and more valuable. In order to make full use of the land resources, architects increase the height of buildings, the tall buildings and high-rise buildings come out; The development and utilization of underground space resources generate the underground buildings, subway and so on; The advent of Subway alleviate the high pressure of transportation on the ground greatly. The most useful method to construct subway is shield method which is used widely now, the mainly reason is that shield method has unique advantages which other methods don’t have in subway tunnel construction. Moreover, shield method also hasn’t high requirements of soil properties. However, there are always two sides to everything decided the shield method also has shortcomings. The ground settlement caused by shield construction and ground movement regularity is always the concerned problems in the process of tunnel design and construction. The main reason which causes appearance and function damage of buildings and structures is the surface subsidence which induced by subway tunnel construction, the economic loss is considerable each year. So the analysis of the surface subsidence regularity caused by tunnel shield construction is very urgent and necessary.The article based on the east stand～tsing lung station tunnel of Nanjing subway line4as the engineering background, and one passage soil features from the tunnel interval is selected to establish3-d numerical simulation model. Analysis the effect which induced by simulate the excavation on surface subsidence. Through the analysis and research, some conclusions with reference value:the surface subsidence gradually increase when the shield is in the process of constantly moving forward, and behind the tunnel excavation face about40meters, the subsidence tends to be stable.15meters of the soil excavation front side slight bulge phenomenon appear; In accordance with the construction sequence, the left line was excavated first, and then to carry on the excavation of the right line, due to disturbance on the surrounding soil induced by the excavation of the left line, cause the soil strength weakening of the right line, so as to make the center line of the tunnel in the right line at the top of the surface subsidence slightly greater than the maximum of the left line;15meters away from front shield machine cutter, the slight bulge phenomenon appear, the early settlement value roughly1～2mm, ahead of the excavation face roughly to-2～-3mm. the subsidence roughly-5～-7mm when the shield through. The settlement value of shield tail roughly-8～14mm, it mainly depends on the rock stable ability; When the outer diameter of shield as, ground surface settlement decrease with the increase of tunnel overburden depth, however, when the depth increases to a certain extent, the reduced amplitude of the surface subsidence is more and more small;Grouting in time or not has a great influence on the surface subsidence, the maximum ground settlement value caused by grouting not timely is the maximum subsidence which grouting condition in time at least2times. The conclusion that surface subsidence mechanism and regularity caused by subway shield construction can provides a certain reference value for similar projects and the construction organization design. |
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