Risk Analysis Of Shenyang North Railway Station With Cover Excavation And Top-down Method

With the increasing population of the world and the rapid development of urban modernization process,urban traffic is no longer a single visible space development to the surface,but gradually to underground development,forming a new era of three-dimensional space city.Because of its many advantages,more and more cities choose to alleviate various traffic problems.Metro stations are often located in busier urban areas.In the process of construction,they often pass through existing buildings such as ground building foundations,underground pipeline galleries and existing metro stations.This will make the stratum face empty,cause stratum loss,and then lead to subsidence and deformation of the upper surface.If the settlement control is not in place,safety accidents will easily occur,resulting in irreparable casualties and economic losses.Among the construction methods of Metro stations,the cut and cover reverse method has become a common method for the construction of Urban Metro due to its advantages of short occupation time,flexible construction organization and high safety factor.In order to avoid the influence of the above-ground and underground risk sources in the construction process and to control the construction cost reasonably,it is necessary to simulate and analyze the whole process of subway construction.Taking Shenyang North Railway Station of Shenyang Metro Line 4 as the actual engineering background,and aiming at the water-rich sandy soil stratum,this paper simulates the construction sequence of the main structure of the metro station by using ABAQUS finite element software,simulates the influence of different construction stages on different risk sources,and compares the numerical simulation results with the normative experience,so as to ensure the safety of the construction.All and dangerous control provides reference basis.The contents of this paper are as follows:(1)Based on the mechanism of surface deformation and settlement and the theory of prediction of surface settlement,the factors causing settlement during excavation of metro station are analyzed,and the allowable values of ground deformation under various building functional requirements,building structure types and stratum conditions are obtained according to the design criteria of building foundation,which are used as follow-up numerical simulation points.Analysis provides reference.(2)Based on the related drawings and Geological Prospecting reports of Shenyang North Railway Station,ABAQUS finite element software is used as the analysis platform to simulate the whole construction sequence of the subway station,and to study the influence of the station construction on the surface settlement and deformation.The results show that with the increase of the depth of foundation pit,the surface settlement increases,and the maximum settlement is at the backfill position above the station,with the settlement of 59.8 mm.(3)Based on the equivalent beam theory and ABAQUS simulation results,the risk sources around the station are analyzed.The results show that the diaphragm wall is subjected to compressive stress at both ends and tension at the middle part along the depth direction,which indicates that the diaphragm wall will be bent under the action of earth pressure,and this form of force is similar to the theoretical sketch of equivalent beam.The horizontal displacement of diaphragm wall increases with the increase of excavation depth.For the intermediate column,the uplift of the base results in the uplift of the intermediate column.For existing buildings,the settlement of the side near the station is always greater than that far away from the station.With the increase of the excavation depth of the foundation pit,the settlement increases from 3.99 mm to 18.25 mm,and the maximum settlement meets the requirements of the code.It is verified that the diaphragm wall has better load-bearing and retaining functions.