Research On The Key Construction Technology Of The New Tunnel Under-crossingexisting Railway Roadbed And The Stability Of The Railway Roadbed

Along with the rapid development of the highway and railway construction in our country,the construction of tunnel engineering advance rapidly at the same time.As a convenient traffic construction,the position of tunnel is always vital whether in mountain ridge or city.The problems need be solved urgently increasing with the development of tunnel engineering.In particular,due to the densest urban facilities,the excavation of urban tunnel will inevitably affect other buildings,while resulting in a series of engineering problems.Based on the engineering example,the key construction techniques of the new tunnel undercrossing the existing tunnel and the influence on the stability of the cross section roadbed were analyzed by the methods of site investigation,physical and mechanical test,FLAC3 D numerical simulation and so on,main achievements and conclusions were obtained as follows:(1)Combined with the project examples,the situation of cross section between existing railway and some one tunnel,the situation of existing railway roadbed,and the situation of undercrossing section of some one tunnel are introduced respectively.By means of datum collection and siteinvestigation,the landform,geological tectonic,lithology of the strata,hydrogeological condition,poor geology,and seismic condition of the project region are summarized and analyzed.(2)By sampling from field,a series of tests such as indoor rock mechanical experiment,rock thermophysical analysis,laboratory soil test,water quality analysis,soil erosion experiment,wave velocity test,and heavy dynamic penetration test(N63.5)are conducted.By analyzing and summarizing the experimental results above,combining the relevant standards and literatures,the corresponding design parameters are recommended.(3)According to the engineering situation and hydrogeological condition,the construction and numerical simulation schemes of the new tunnel undercrossing the existing tunnel are introduced.The key construction technologies of thenew tunnel undercrossing the existing tunnel such as construction survey,little tremie pipe construction,tunnel excavation,steel frame construction,steel mesh construction,rock-bolt construction,concrete cushion construction,waterproofing layer construction,secondary lining construction,and construction of grouting behind the initial support and secondary lining are analyzed.Furthermore,the quality control various aspect of links in tunnel constructing are described.(4)The new tunnel undercrossing the existing railway will affect thestability of railway roadbed.After completion the new tunnel,the maximum subsidence of existing railway roadbed occurred in the cross section between down-link of existing railway and subsurface excavation section of left-link of new tunnel.With the gradual excavation of the subsurface excavation section,the roadbed settlement of the cross section between subsurface excavation section of the new tunnel and the up-link and down-link of the railway is gradually increasing.After completion secondary lining in cross section of the new tunnel undercrossing the existing railway,the longitudinal settlement curve of the existing railway roadbed is similar to normal distribution.With the gradual excavation of the subsurface excavation section of the new tunnel,the settlement of the new tunnel and the roadbed of overhead contact line is gradually increasing.