Numerical Simulation Analysis On Ground Surface Settlement Induced By Subway Shield Construction

The shield driving method has been one of the main construction methods in the urban tunnel . The soil sedimentations and ground movements caused by shield tunneling are the problems highly concerned in the design and construction process of shield tunnel. Ground surface settlement induced by subway tunnel construction and post-construction is the main reason which cause kinds of buildings damaged in appearance and fu nctions.Futhermore,it brought great economic losses every year.So, The research on ground surface settlement and soil lateral displacement induced by shield tunnel is very urgent.This paper ,combining Xi'an Subway Construction,adopts the FLAC3D as compute tool which is three dimensional explicit finite-difference program for enginneering mechanice computation and establish the model of metro shield construction process to simulate the excavation and deformation of tunnel.This paper analyses the discipline of ground movements induced by shield tunnel construction,as well as,analyses some factors affect ground settlement such as the time about grouting,soil pressure on cabin and the thick-ness of over-buried layer and so on.By the numerical simulation study,some useful conclusion as follows:Surface subsidence increases as the advance of shield and reach the maximum after the tail of the shield about 30m.Tts maximum is 17.1mm.The lateral horizontal displacement of ground mass increases as the advance of shield ,tend to stability after the tail of the shield about 30m.The longitudinal horizontal displacement of the monitoring point is opposite with moving direction of shield as the shield gradually close the monitoring point;after shield passed the monitoring point,it is identical with moving direction of shield. If grouting is not timely,the maximum of ground surface settlement is about 2 to 5 times of grouting in time.Grouting in time is a key factor to minish stratum loss.In order to control the ground settlement,increasing soil pressure in cabin only play a finite role ,or it is not appropriate at all,on the contratry,it can increase the ground settlement.So it shoud is consistent with original soil pressure.The subway shield construction ground settlement mechanism and law obtained from the reserch can offer the reference value for the similar project plan determination and construction organization plan.