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

With the continuous development of economic construction, urban population increases quickly, the ground space pressure is more and more serious. The development and application of underground construction is necessary. In order to effectively solve the problem of traffic congestion, the subway arises at the historic moment. In the process of subway construction, because the underground soil is dug out, inevitably produce the surface subsidence. The deformation affects the normal use of the surrounding buildings and pipelines, therefore, the study of surface subsidence rule of the construction of underground is very important.Firstly, the numerous domestic and foreign scholars on the research achievements of the ground settlement caused by subway construction are summarized, and the shallow depth excavation method construction technique and monitoring measurement technology are described. Combined with the Beijing metro line subway station 7 and 14 line subway station, main body of 84 monitoring sections, affiliated 60 monitoring cross section, interval 20 monitoring cross section, a total of 164 cross section, and eliminate the abnormal data in nine monitoring cross section, the final selection of 155 section of locale measurement of the actual monitoring data is analysised. Supplemented by FLAC3 D numerical simulation, the shallow depth excavation method of surface subsidence rule of the construction is carried on the thorough research. And through the study, PBA method in the construction of the station main body for small pilot tunnel excavation methodis optimized.In this paper, main conclusions are as follows:1. Values of ground surface settlement during upper bench cutting occupy total settlement values among 60%~70% in the construction of bench cut method;2. The construction over the tunnel gives tunnel overburden, change the stress distribution in the soil, increase the surface settlement, and makes the settling tank is relatively flat, wider3. In shallow buried tunnel, construction methods and tunnel cross section shape have a lot of influence on the settlement trough width.Different construction methods of settlement groove width from big to small order: PBA method >middle hole method> CRD method;4.Depth-span ratio increase makes settlement groove widthsmaller, width of settlement curve parameters and corresponding smaller, and the stratum loss rate is also reduced. Under the condition of clay and sand, the arching effect of depth-span ratio isbetween 1.2 to 1.5;5.In small pilot tunnel construction of PBA method, by using “upper first, the crisscross excavation construction scheme”, the settlementand disturbanceis smaller. Through the field monitoring measurement and numerical simulation results, the calculation result is more reasonable, can provide a reference for future design and construction;...