The Surface Settiement Behind Retain Wall Regularity Research Of Subway Deep Foundation Pit

The rapid economic development has led to the accelerated process of urbanization, urbandevelopment with the traffic pressure on makes people to develop underground rail transit. Thesubway has significantly eased the ground traffic pressure, and has solved the impact of groundtransportation on the environment, but at the same time subway project as one of theunderground building works, its impact on the environmental can not be ignored. Foundation pitdeformation has become an important topic of scholars and technicians, Surface subsidence asthe most important manifestations of the impact on the surrounding environment, Its form ofdistribution, variation and Influencing factors is especially important.In this paper, through the presentation of foundation pit deformation theory, foundation pitdeformation mainly include three aspects, basement uplift, enclosure structure and the surfacesettlement behind retain wall. There are several ground surface settlement theories of thecalculation method, the ground loss theory is used widely, it consider enclosure structure andsurface deposition of a quantitative relationship, in the later chapters that will be chosen foranalysis. Moore Coulomb soil model is only a cursory analysis of the foundation pit, not reflectthe deformation of the pit accurately, because of it can only reflect the soil dilatancy, not reflectthe wall surface subsidence. Modified Cambridge model can reflect the soil ’s shear reduction,and be used for analysis of the surface settlement behind retain wall. After a preliminary analysis,the more significant parameters on surface settlement are: poisson ratio internal friction anglecompression and rebound parameters, this will be used for the later chapters. This article rely onthe14th line subway station foundation pit, the calculation analysis of the impact that factorsaffect surface settlement, result shows the effect of the presence of corner, the scope of thisproject is about half of the pit width, in the case of same excavation depth, the main three factorsthat affect surface settlement are: steel prestressed support, envelope insertion ratio, the stiffnessof the support system, then the support location and excavation methods, bar reinforcement forreducing the surface settlement and pile horizontal displacement was not significant (Beijingarea). The ratio between surface maximum settlement from the excavation depth is:0.052%—1.1%；The maximum pile horizontal displacement and excavation depth ratio range:0.11%—0.2%.The ratio between pile deformation area and surface subsidence area is1.45, notof the soft soil area. After the calculation of a variety of situations, The surface settlement behindretain wall follows the normal curve, there is quantitative relationship between the largestsettlement location and excavation depth, there is a direct relationship between surfacesettlement (>1mm) scope、pile insertion ratio and the length of the envelope pile. Finally, there is a brief discussion of the foundation pit dewatering on surface settlement in the Beijing area,and foundation pit dewatering of a month result in stabilizing of pit surface settlement.