Study On Optimization Of Excavation Supporting Design Near Metro In Soft Soil

With the rapid development of urban rail transit,foundation pit projects which are adjacent to subway tunnel gradually increase.Especially in soft soil area,adjacent excavation will destroy the original soil stress balance,resulting in large displacement and deformation of the tunnel.In addition to the safety and stability of the excavation,the design of the excavation should ensure the normal operation of metro facilities and reduce the engineering cost as far as possible.Therefore,it is of great practical significance to study the optimization design of excavation adjacent to subway tunnel in soft soil area.In this paper,the optimal design of the Wei Dong excavation adjacent to Hangzhou Metro Line 1 is studied.Firstly,cases of excavation adjacent to subway tunnel in soft soil area were collected,the common support forms and detail parameters of support structure of the excavation were studied.Secondly,taking the optimum design of Wei Dong excavation as an example,orthogonal experimental design and fuzzy comprehensive evaluation are applied to determine the optimized detail parameters of support structure.Finally,the optimization scheme of excavation was verified and the design was further deepened.The main results of this paper are as follows:(1)A case study of 40 excavations which are adjacent to subway tunnel in soft soil area was considered.The influence of the relative position between the excavation and tunnel on the tunnel displacement was analyzed.The common support forms and reasonable range of detail parameters of support structure of the excavation were concluded.Besides,common design and construction technical measures were introduced in excavation adjacent to subway tunnel.(2)Taking " rowed piles + 2 reinforced concrete internal supports " supporting and protection scheme as an example,the optimization method of supporting structure detail parameters based on orthogonal test design was introduced.In the optimization problem,the pile diameter,the net spacing of the piles,the length of the pile,the vertical spacing and the cross-sectional area of each support were taken as the design variables.Furthermore,lateral displacement of the pile,maximum horizontal displacement of the tunnel,maximum vertical displacement of the tunnel and engineering cost were considered as evaluation indexes.PLAXIS finite element software was applied to calculate the deformation of tunnel and adjacent excavation.The membership degree of fuzzy comprehensive evaluation was introduced to solve the problem of multi index contradiction.Besides,the range analysis of comprehensive evaluation membership was implemented.Therefore,optimal combination scheme of supporting and protection structure detail parameters was obtained.(3)Based on the optimization design of Hangzhou Wei Dong excavation,orthogonal experimental design method was applied.Due to a totoal of 7 design variables,L49(78)orthogonal table was selected,each design variable was given 7 levels.49 orthogonal tests was carried out to calculate the 4 evaluation indexes.The weight of each evaluation index was determined by analytic hierarchy process.The membership degree of fuzzy comprehensive evaluation was calculated.And then,the range analysis of the membership degree of fuzzy comprehensive evaluation was calculated to determine the optimal supporting and protection structure detail parameters.Finally,the optimal supporting arnd protection structure detail parameters were verificated,and the design of supporting and protection scheme was further deepened.