The Research On Numerical Simulation Of Deformation Behavior And Building Envelope Of Deep Excavation In The Soft Soil Area

With the acceleration of urbanization in our country, many infrastructure need to be built. Various underground building and facilities will get rapid development. The first problem to those projects is the large-scale excavation. The influence on deep excavation itself and surroundings environment is one of the most important research content of deep excavation.This research is based on the actual situation of deep foundation pit excavation of the subway station in the city of Hangzhou. Through the method of numerical simulation, the research is made on the changes of the horizontal displacement of the diaphragm wall, the surrounding ground settlement and the earth pressure during excavation and the factors which can impact greatly the horizontal displacement of the diaphragm wall, the surrounding ground settlement and the displacement of the railway embankment. The main contents of the result are as follows:(1) With the increasing depth of the excavation, the horizontal displacement of the diaphragm wall and the surrounding ground settlement are increasing with each step change roughly proportional to the excavation depth, the earth pressure is deceasing.(2)The reinforcement is the most common method to reinforce the foundation. The results of simulating the process of deep excavation in the state of reinforcement and un-reinforcement show that the horizontal displacement of the diaphragm wall, the surrounding ground settlement and the displacement of the railway embankment can be greatly deceased by reinforcing the earth near the deep excavation. Reinforcing the earth is the most effective method to strictly control the displacement to match the requirements of the surrounding environment.(3)The thickness of the diaphragm wall is directly related to its stiffness. The results of simulating the process of deep excavation in different thickness of diaphragm wall, such as 0.6 m, 0.8 m,1.0 m,1.2 m,1.4 m,1.6 m respectively, show that the horizontal displacement of the diaphragm wall, the surrounding ground settlement and the displacement of the railway embankment can be deceased by increasing the thickness of diaphragm wall. But if the thickness is more than 1.4 m, the obvious results cannot be got. It is best to control the thickness in 0.8 m ~ 1.4 m.(4) The depth of the diaphragm wall is one of the most important parameter in designing deep excavation. The calculation results of simulating the process of deep excavation in different depth of diaphragm wall, such as 55 m, 53 m, 50 m, 48 m, 46 m, 44 m, 42 m, 40 m respectively, show that with the gradually decreasing of depth, the horizontal displacement of the diaphragm wall under the final excavation plane increase significantly, the settlement of the earth surface close to the edge of the pit gradually decreases, the settlement of the earth surface far from the edge of the pit gradually increases and the displacement of the railway embankment reduces.(5)The stiffness of the support is the most important parameter of support system. The calculation results of simulating the process of deep excavation in different stiffness of the support system, such as 0.5 times, 1.0 times, 2.0 times, 4.0 times, 6.0 times, 8.0 times, 10.0 times the original design of stiffness respectively, show that the horizontal displacement of the diaphragm wall, the surrounding ground settlement and the railway embankment will reduce if the stiffness of the support system is increased. But no obvious effect can be got if the stiffness is more than the design value. The supporting stiffness of original design satisfies the engineering requirement.