| Deep foundation pit excavation and precipitation will cause soil deformation,which will lead to the deformation of nearby subway tunnels.The research on the influence of deep foundation pit on nearby subway tunnel is a hot topic in civil engineering field.A large deep foundation pit excavation project near Nanjing Metro Line 2 covers an area of about 32,000 square meters and an excavation depth of about 20 m.The foundation pit is relatively close to the existing tunnel.Based on the background of this project,in this paper,the influence of foundation pit excavation on the adjacent subway tunnel and its law are studied by the collection of a large number of relevant data,the finite element simulation method and comparison with the on-site monitoring data.The main research contents and conclusions are as follows:(1)After consulting and referring to a large number of relevant data,the relevant research methods such as centrifugal test method,theoretical analysis method,numerical simulation method and field measurement method are summarized and analyzed.The twenty practical engineering cases of foundation pit excavations affecting adjacent existing tunnels are collected and summarized,and with the mathematical statistics,the different influencing factors of adjacent tunnel deformation caused by foundation pit excavation are analyzed.(2)Based on the background engineering data,a three-dimensional finite element calculation model is established.The Molar-Coulomb elastic-plastic model is used to study that under five excavation depths,the supporting deformation of foundation pit,ground settlement above tunnel,uplift of foundation pit bottom and deformation of tunnel lining structure.The study shows that: the foundation pit ground wall deforms into the foundation pit,the foundation pit supports deform vertically downward,the foundation pit bottom is uplifted,the ground settlement above the tunnel is concave curve,and the maximum settlement occurs at the place nearest to the foundation pit.The lining structure of the tunnel displaces downward and toward to the foundation pit,and with the deepening of excavation,the displacement value gradually increases,with the maximum settlement component of 3mm and the maximum horizontal displacement component of 4mm toward to the foundation pit.(3)In order to predict the deformation of soil under the effect of excavation unloading and precipitation,and the deformation of nearby tunnels more reasonably,the hardening soil model was used to study the influence of the unloading modulus and the loading modulus on the deformation of foundation pit.The calculation results show that the bottom rebound value of the foundation pit using the hardened soil model is smaller and more in line with the actual situation.At the same time,the influence of precipitation on the deformation of subway tunnel is studied,and it is found that the deformation value of tunnel obviously increases after considering precipitation,and the influence of precipitation on underground engineering should be reasonably considered in future practical projects.(4)By comparing the finite element analysis results with the field measured data,the deformation rules of the two are consistent.The tunnel settlement and horizontal displacement curves are concave,the maximum measured settlement component is 5mm,the horizontal displacement component towards the foundation pit is 6mm,and the shape variable is within the safe range. |
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