Study On Deformation Discipline Of Shallow Tunnel Excavation In Beijing Subway Construction

With the rapid pace of urbanization, the level of economic developmentcontinues to improve,expanding the size of the city,traffic increasing pressure topromote the rapid development of underground public transportation that is thesubway.But there are too many people and buildings in the subway constructionarea,due to the constraints of the surrounding environment shallow constructionmethod generally adopted.Construction of metro cities in our country are generallyvery complex in geological conditions,therefore constant danger occurs,bring a lot ofaccidents,in this context,to find out the Shallow deformation of subway tunnel,takesupplementary measures to advance security,a reasonable choice of the excavationand support methods to ensure the safety of construction is very important.In this paper, The research situation on tunnel stability analysis is simplelysummarized, Shallow construction methods and monitoring techniques commonlyused of city subway tunnel were analyzed.Through the combination of Beijingsubway engineering data,using a combination of actual monitoring results, thetheoretical analysis calculation and numerical simulation methods,to study the reasonsof tunnel deformation and to study on Deformation Discipline of Shallow TunnelExcavation, Draw the following conclusions:1. On the pipeline deformation monitoring standards measuring point must belaid.In the tunnel excavation process,with the advancing of tunnel face the verticaldisplacement accumulated deformation speed are increase when the section does not arrive, andthe rate has been decremented when the section passed,distribution is consistent with theexponential function. The main reasons of Deformation are Precipitation, Groups tunnel effect,bigpipe shed and Stratigraphic holes.2. The vault final settlement by theoretical formula calculation is35.75mm,anastomosis with the actual monitoring data30-40mm. Vault settlement exists lagmonitoring,the prediction of the actual settlement up to60mm, During the excavation vault settlement accounts for60%of the surface subsidence.Variation of the sidewall convergence aresimilar to vault settlement.3. There are some differences between actual monitoring data and numericalsimulation results, but basically the same in deformation discipline. The maximumdisplacement of shallow tunnel occur in the vault site and by the middle of the sidewall. In the double tunnel the minimum value and the impact on the surroundingranges occur in the condition that tunnel excavation at first and then the tunnelexcavation below. Advanced small pipe grouting can reduce vault settlementsignificantly andthe control effect of up to30%,but the control effect on the side wallof the convergence is not obvious.4. In the process of excavation by step method, settlement caused by excavation onthe steps to achieve41.83%of the total and sidewall convergence reached33.02%ofthe total value, the lag monitoring value of vaults and converges up to more than40%and30%, respectively. Multi-pilot tunnel excavation by away from7D distance ofabout30m in vertical direction and the changes of stress state is the main reasoncausing settlement.