Research On Surface Subsidence Law Caused By Shield Construction Of Beijing Metro No.16 Line

Shield construction of subway tunnel will inevitably lead to surface subsidence,the study of which will be of vital importance to the safety of construction and operation.This paper is based on Wenyang lu station-Daoxianghu lu station of Beijing No.16 Line,analysis the law of surface caused by shield construction through the method of theory analysis and Site monitoring measurement and numerical modeling.The main work and conclusions are as follows:(1)The mechanism of surface subsidence caused by shield construction is mainly due to the disturbance of soil during construction,which depends mainly on the characteristics of the rock and overlying strata.The subway is a two-lane tunnel,along the geological conditions are complex and varied,the soil layer which the tunnel through is silty layer,silty clay layer and the coarse sand layer,The soil above the tunnel is reclamation soil layer,silt layer,silty clay layer,the stability of the soil around the tunnel is poor and the strength is low,and soil layer prone to collapse and gushing water.(2)Through the comprehensive analysis of 13 surface subsidence monitoring data along the line obtain results: the settlement value of each section is quite different,the maximum settlement is 14.3mm,the minimum is 7.3mm,this is mainly caused by the different geological conditions of the sections,but the surface subsidence values in the sections are less than the control standard of surface subsidence caused by shield construction in Beijing which is 20 mm.(3)Through the typical cross-site detection and numerical simulation analysis obtain results: the lateral subsidence of the single-line excavation is the subsidence of the grooved surface,the lateral subsidence of the two-lane tunnel is "W",its influence range and settlement have obvious superposition effect,the main influence area is 7m to 12 m meter outside the center line,the total surface subsidence area is within the range of 22 m to 30 m outside the center line.The better the geologic conditions(compactness,self-stabilizing ability),the smaller the surface subsidence,and the deeper the tunnel is buried the smaller the surface subsidence.(4)The longitudinal subsidence law has obvious stage,before the arrival of the shield machine,the surface subsidence accounts for only 5 to 15 percent of the total settlement,when the shield machine through the process,the surface subsidence accounts for only 45 to 50 percent of the total settlement,after the shield machine through,the surface subsidence accounts for only 40 to 45 percent of the total settlement.The subsidence curve is similar to the two smooth segment exponential functions symmetrical with the anti-bending point.The influence area is 15 meter in front of the cutter head of the shield machine and Shield machine cutter through 30 m distance.