Study On The Construction Monitoring And Numerical Simulation Of A Deep Foundation Pit In Lanzhou Metro Station

As a few cities in China to build subway in loess area,metro construction is the first time in Lanzhou.Past experience is not to be copied,especially for Pile Bracing Structure Design and construction.There are still many problems in practice,which make the foundation pit unstable due to the instability of excavation.A slight carelessness can lead to engineering accidents.Considering the unique hydrological and geological form of Lanzhou,the subway project is also a project with high social concern and complicated design and construction.The design and construction problems that may be encountered in large-scale construction of subsequent lines.Lanzhou metro construction is still in its infancy,and the theory is far behind practice.Therefore,in order to ensure the safety of the foundation pit itself and the stability of the surrounding environment,it is necessary to analyze the stability and deformation of the deep foundation pit in Lanzhou metro station.Based on this,the paper takes the deep foundation pit of one station of Lanzhou Metro Line 1 as the research background,and uses the method of field monitoring data analysis and three-dimensional numerical simulation to study the influence of foundation pit excavation on the surrounding environment.The main contents and achievements of this paper are as follows:(1)Based on the geological survey and design data,this paper gives a detailed introduction to the landform,geomorphology,engineering hydrogeology and support structure of the project,focusing on the design of the supporting system for the foundation pit bored pile + multi channel support,and provides detailed information for the analysis of the follow-up problems and the modeling of the software.(2)The deep foundation pit of Lanzhou subway station adopts the support form of bored pile plus multi-channel support,which has obvious effect of water interception and larger safety reserve.The displacement of diaphragm wall,ground settlement,underground water level and supporting axial force change little,which meets the engineering design requirements.The construction load of bored cast-in-place pile is easily shifted to one side at the top of the bored pile,and this phenomenon is particularly obvious when the depth of the excavation is larger.(3)The modified Cambridge model can better reflect the degeneration characteristics caused by excavation of deep foundation pit of Lanzhou metro station.The surface settlement curve around the foundation pit presents a "groove type".After calculation,the maximum settlement of the earth surface is about 0.05H%,and it appears at 0.64 H from the edge of the foundation pit.The horizontal displacement curve of cast-in-place pile shows a "belly type".The maximum lateral displacement value is about 0.09H%,and it appears at the H-6 distance from the top of the foundation pit.