Research On Deformation Behavior Of Deep Excavation With Bracing Diaphragm Wall In Hangzhou Area

In recent years, the urban construction is speeding in China. Underground space resources have been developed unprecedentedly. Hence a large number of deep excavations have been constructed. It is significant to study the deformation of the excavation and its surrounding environment. Many scholars have made a number of meaningful conclusions based on a great quantity of research for excavation engineering. But excavation engineering is a subject with strong regional characteristics. It needs to be discussed whether the results of excavation engineering in other areas can be used directly to predict the deformation of deep excavation in Hangzhou area. Therefore, it is necessary to systematically study and analyze the deformation behavior of deep excavation in Hangzhou area. In this paper,the deformation behavior of the deep excavation with bracing diaphragm wall in Hangzhou area is studied deeply based on the statistical analysis of the excavation cases, the actual engineering analysis and the finite element numerical simulation. The main research results are as follows.1. A database of 18 case histories of deep excavations with bracing diaphragm wall in Hangzhou area is collected. Based on the statistical analysis of the data, the deformation behavior of deep excavation with bracing diaphragm wall are studied. The range, mean value and location of the maximum lateral displacement of wall are proposed. Factors such as the insertion ratio and the stiffness of the supporting system which affect the maximum lateral displacement are analyzed. The range, mean value and location of the maximum ground surface settlement are also proposed. The relationship between the maximum lateral displacement of the diaphragm wall and the maximum ground surface settlement is analyzed. The above results are compared with those of other soft soil areas.2. Measurement analysis is carried out on one excavation located in Hangzhou. The observed results show the maximum horizontal displacement of the excavation in this chapter is very close to the mean value in the above analysis. The horizontal displacement and surface settlement induced by creep can not be ignored. The time history curves of the surrounding pipeline and road settlements can be divided into three stages: (1) the rapid subsidence stage;(2) the fluctuation stage; (3) the stabilization stage. The internal force variation of the internal support system induced by excavation is studied. And the changing processes for the vertical displacements of the wall and column piles and the water level are analyzed.3. The deformation behavior of the excavation in the above chapter is simulated by setting up a three-dimensional model using the finite element software PLAXIS 3D in which the soil is simulated using the HSS model. The rationality of the calculation model is verified by comparing the calculated results with the measured data. It can be found that the results adopting HS model are too large by comparing the calculated results adopting HSS model and those adopting HS model. The effect of the passive zone reinforcement and the form of the strip improvement are discussed deeply. The results show that the control effect of passive zone reinforcement on excavation deformation is comparatively obvious. There is an effective range for the width of skirt border reinforcement. When the width exceeds a certain value, the maximum horizontal displacement of the diaphragm wall and surface settlement decrease more slowly. In the case of the same project cost, the combination of intermediate strip reinforcement and skirt border reinforcement can greatly reduce the surface settlement outside the midpoint of the excavation. Therefore, from the point of view of control settlement, intermediate strip reinforcement is better than the two sides strip reinforcement.