Study On Surrounding Rock Pressure And Structure Supporting Mechanism Of Large-span Shallow Buried Metro Station Tunnel In Mountainous City

Mountainous city refers to towns or cities built on mountainous areas,sitting on uneven land field and complex landscape,totally different in physical existence and geographic conditions from that of the cities on plain.There are quite a few mountainous cities including Chongqing,Guiyang,Urumqi,Naning,etc.,among which Chongqing is the most typical one.Large-span shallow buried tunnels have kept increasing as railway construction boomed in mountainous cities.Due to limited amount of such type of projects,large-span shallow tunnels need to be comprehensively studied.The study is supportted by Chongqing Science and Technology Commission(No.cstc2009AB6194).Based on the construction of subway stations on Chongqing Rail Transit Line 1,Line 3 and Line 6,this dissertation studied stratum deformation,structural stress characteristics,and submersion dividing line of large-span shallow tunnels in mountain cities.This paper was conducted through theory study,simulation experiment,and numerical calculation.The main work is summarized as follows:(1)The complex variable function method,Laplace transform and superposition principle for viscoelastic cases were used in the derivation of excavation induced displacements and stresses around the tunnel.This method is applicable to calculate the deformation of shallow buried tunnel due to excavation in arbitrary viscoelastic model.(2)Based on the stratigraphic deformation obtained in the last step,the Winkler hypothesis and local elastic model to solve the support pressure.Then the internal force is derived naturally.With some concrete examples,in view of the generalized Kelvin viscoelastic model,the evolution of settling vessel,the characteristics of vertical displacement over time,the influence of tunnel span and buried depth on ground surface settlement,the variation of support internal force and the influence of tunnel span and buried depth on support internal force are discussed.(3)According to the displacement solution of shallow buried tunnel under rheological condition,a method of deep subdivision of subway station based on displacement field is proposed.The nonmonotonic characteristics of the displacement field of the surrounding rock of shallow buried tunnel,the time effect of the surrounding rock pressure arch and its influencing factors are analyzed.Also provide basis for subsequent analysis.(4)Through simulation experiments on the mechanical behaviors of large-sapn shallow subway station tunnels,the stress of the straight wall and the settlement law of the ground surface were studied(5)Based on transparent soil experiment technology and PIV measurement technology,a two-dimensional tunnel excavation simulation was conducted according to the similarity principle.Under the same condition,control of a single variable,the influence of buried depth span on pressure arch of the tunnel was studied respectively.The experimental results show that the depth of the tunnel is not only connected with the tunnel,but also depends on the tunnel span.(6)The model test and field test are in agreement with the results of 3D numerical analysis,which verifies that 3D numerical analysis could be used to guide the design and construction of such tunnels.The study improved awareness of the law of the construction mechanics of large-span shallow buried tunnels.It could be a reference for similar engineering design and construction.The results coud be used in design manuals or standards.