| As metro is a kind of quick and convenient green transportation, it can solve traffic jam and enhance reasonable distribution of cities. With the process of rapid development of domestic subway construction in recent years, ground surface deformation under construction brings negative effects to surrounding environment. It has great significance to study the surface deformation in order to probe into reasonable construction methods and protective measures. On the basis of one subsurface tunnel in Xi’an Metro Line 4, this paper combined numerical simulation with field monitor measuring to study the influence factor of surface deformation, main results are as follows:First of all, ground deformation mechanism of tunnel excavation is analyzed, the longitudinal and transverse deformation law of ground surface and settlement controlling measures of tunnel are summed up in detail.Secondly, the construction process of metro and influencing factors of surface deformation are simulated by finite element software ANSYS. The simulation results shows excavation has obvious effect on surface settlement and crown settlement when rock grading is increasing, pre-supporting at tunnel arch can reduce settlement evidently while pre-supporting on bottom of tunnel has little effect on settlement reducing. Results of settlement control is best by CRD construction method which can minimize surface deformation, rate of surface horizontal sedimentation slow down gradually and its influence range is decreasing then the benching tunneling construction method, the entire section method afterward. The influence scope of procession excavated tunnel is about double tunnel diameter distance from posterior excavated tunnel face, the maximum impact occurs when posterior excavated tunnel reached monitoring section of procession excavated tunnel.Finally, conclusions are obtained by comparing numerical simulation results with monitoring results. Maximum rate of settlement can reach 1.5mm/d during rapid change period of settlement. Ground deformation reaches one half of steady deformation when tunnel face meets monitoring section. The maximum surface settlement is 19.1 millimeters which caused by single line tunnel excavation, width of surface settlement tank is 8.8~9.3 meters. |
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