The Effect Of Surface Settlement Of Subway Station With Different Shallow Tunnel Construction Methods

With the character of flexible excavation methods，little environmental pollutionand low project cost, the shallow buried covered excavation method in the metroconstruction attracts more and more people’s favor. Underground rock excavationinevitably disturb the surrounding strata, causing geostress redistribution and groundmovement, resulting in surface subsidence. If deformation is too large, the adjacentbuilding maybe tilt, cracking or the underground pipeline destructed. Because theconstruction procedure and supporting structure with different tunnel constructionmethods in different depth are variant, the settlement amount and settlement law arealso different. So it is necessary to do a full research in the deformation mechanismoccurring in surface subsidence, and to seek the settlement law and basiccharacteristics in the surface settlement at different depths with different excavationmethods. Meanwhile, predicting the surface subsidence by numerical calculation andproposing further reasonable relevant measures and construction methods are allsignificant to the design and construction of the underground station and the adjacentbuildings.This paper uses Qingdao Metro (line3) Jiangxi Road Station as the background,studies the settlement law in different tunnel construction methods and different depthby numerical calculation. The work done and the results achieved in the course of thestudy are listed as follows:(1) Describing the settlement mechanism and deformation law on the formationby excavation construction, explaining the strained condition and trends from amechanical point of view of the surrounding rock. It also gives the reasonable controlof ground settlement countermeasures combined with the actual construction.(2) Reasonable and correct simulation of the station excavation support process as well as the mechanical effect of the various support measures to predict the results’correctness is very important in forecasting station surface subsidence caused by theexcavation.(3)Considering the progress of the excavation and the monitoring data of thetunnel ground subsidence of Jiangxi station, the text analyses the ground subsidenceand obtains its vertical changing rules and horizontal one and discovers the settlementvalue of the first excavation is greater than the settlement value of the later side in thesame slip. Then the actual progress of the excavation is calculated by the FiniteElement Program named Plaxis3D Tunnel and takes out the ground subsidencechanging rules caused by each step’s excavation during the upper steps’ construction，also make a comparative analysis with the calculated results and the actual values..(4) Combined the Jiangxi station’s background, the text does numerical simulationon the double-side-wall heading constructing method and the CRD excavation method,gets when the cross-cover ratio smaller than0.62the ground settlement value of CRDexcavation method is bigger than the the double-side-wall heading constructing method.Then it points out the dangerous construction sequence and gives correspondingmeasures so as to improve the construction safety.The above research is based on the theoretical study, combining the monitoringdata’s analysis and the numerical simulation. They all help bring out a big step in thestudy of the shallow buried covered excavation method in rock and soil areas. Theachievement is full of referential meaning and practical application value in theengineering construction in this area and other regions with similar geologicalconditions.