| With the rapid development of China’s economy and society and the continuous advancement of urbanization,the design of urban high-rise buildings and the use of underground space are more and more.The development of urban underground space in the future will become bigger and bigger with the increase of people’s demand.This also means that underground structure will become deeper and more complex.So similar deep foundation pit engineering is an important research topics at present.This paper based on the actual data of foundation pit engineering of Heping street Station of Changchun Metro Line 2,the whole process of foundation pit excavation is simulated by FLAC3 D finite difference software.At the same time,through the analysis of elastic modulus of soil,friction angle of soil,overload of ground,spacing of internal support and stiffness of retaining pile,the deformation law of foundation pit under different factors is studied.The main results are as follows:(1)The results of numerical simulation show that with the increase of the excavation depth of foundation pit,the ground settlement around the foundation pit increases first and then decreases,and the maximum value of ground settlement occurs 15 meters away from the edge of the foundation pit,which is about 0.8 times of the excavation depth of the foundation pit.Horizontal displacement of retaining structure increases with the increase of excavation depth.At the same time,the deformation law of each working condition is basically the same.Basically,the maximum value appears near the excavation surface,and the deformation curve is approximately "parabolic".(2)Comparing the numerical simulation results with the measured results,it shows that although there are some differences between the two values,the overallchange law shows the same trend.Basically,it can be considered that the foundation pit model established by FLAC3 D is correct and feasible to simulate excavation.(3)Natural factors research shows that the horizontal displacement deformation curve of the enclosure structure and the settlement deformation curve of the ground around the foundation pit will change with the change of the elastic modulus of the soil and the friction angle of the soil.The changes of the elastic modulus of the soil and the friction angle of the soil have stronger influence on the surface settlement than on the horizontal displacement of the enclosure structure.The construction factors show that the change of overload has a great influence on the ground settlement deformation around the foundation pit and the horizontal displacement of the retaining structure.The study of design factors shows that the change of pile diameter of retaining piles has a stronger effect on the deformation of foundation pit than the change of spacing of retaining piles,but neither of them has a great influence on the deformation of foundation pit.The influence of pile spacing on surface settlement and deformation is almost the same as that of horizontal displacement and deformation of enclosure structure,but the overall effect is not very great.Generally speaking,the deformation of foundation pit is more sensitive to the change of pile diameter,which is slightly stronger than the change of pile spacing.In addition,reducing the spacing of internal support can appropriately restrain the surface settlement and the horizontal displacement deformation of the enclosure structure.(4)Based on the analysis of the factors affecting the deformation of foundation pit,three methods are determined to control the deformation of foundation pit:adjusting the strength of soil,adjusting the spacing of steel braces and adjusting the stiffness of retaining piles.The cost calculation and comparison of the above three methods for controlling the deformation of foundation pit show that adjusting the steelsupport is the most economical and convenient method in the process of foundation pit construction. |
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