Study On Deformation Mechanism And Control Of Underground Metrol Tunnel Caused By Large Excavation With Segregate Shafts

Controling the uplift deformation of the subway tunnel caused by unloading of excavation in the water rich soft soil reclamation area is essential to the structure and operation safety.In this dissertation,based on the deep excavation project of Shenzhen water rich soft soil reclamation area,the deformation mechanism of metrol tunnel is studied with theoretical analysis,soil parameter test and numerical simulation method.（1）Based on the rebound deformation of soil,a mechanical model of the deformation of the existing tunnel caused by foundation pit excavation is proposed.Based on the soil rebound deformation theory,the mechanical model of tunnel deformation caused by foundation pit unloading is established by the method of additional deformation and weighted residual value.The analytical solution of tunnel deformation caused by foundation excavation is derived.The calculation software of tunnel deformation caused by foundation pit excavation unloading is compiled.The influence of excavation depth of foundation pit,embedded depth of retaining structure,bending rigidity of tunnel and clear distance between foundation pit and tunnel on deformation of underlying tunnel are analyzed,which provides basis for scientific excavation.（2）The unloading ratio and rebound deformation parameters of foundation pit in coastal soft soil area are studied.The unloading ratio and rebound deformation parameters of foundation pit in coastal soft soil area are studied by consolidation unloading test method.The critical unloading ratio and ultimate unloading ratio are obtained by lateral stress relaxation method,unloading K₀ method and rebound deformation modulus method respectively.The exponential curve fitting formula of unloading ratio and rebound deformation modulus is obtained.The test results show that the maximum influence depth of rebound deformation of foundation pit excavation in Shenzhen coastal soft soil area is 2.05 times of the depth of excavation;0.75 times of the depth of excavation,which is the main reinforcement area.（3）Numerical simulation studies the influence of subway protection and reinforcement measures such as different excavation schemes and foundation reinforcement on tunnel uplift deformation.Several groups of FLAC 3D numerical models are established to study the influence of different shaft sizes,excavation sequence and diameter of uplift pile on the uplift deformation of underground tunnel.The control effects of root pile foundation reinforcement,uplift pile uplift plate structure system,and shaft type subregional excavation on the uplift deformation of underground tunnel are studied.Shaft type subregional excavation is the most effective way to control the uplift and deformation of the tunnel.（4）This dissertation proposed an optimization construction scheme of tunnel deformation control based on the vertical shaft partition skip excavation combined with anti-uplift structure system.Based on the case of Qianhai underground road excavation crossing Metro Line 5 and line 11 in Shenzhen,the FLAC 3D numerical model is established to study the deformation mechanism and control effect of underlying tunnel uplift caused by excavation unloading.The results show that the theoretical model calculation results are close to the numerical simulation results.This dissertation reveals the mechanism of foundation pit reinforcement in controlling tunnel deformation and the influence of foundation pit excavation construction scheme on the structural deformation of subway tunnel.This dissertation puts forward the optimization construction scheme of tunnel deformation control based on vertical shaft partition skip excavation combined with anti uplift structure system.（5）The structural system,design method and key construction technology for controlling the uplift of underground tunnel based on sectional excavation of shaft type foundation pit are proposed.This dissertation presents the design method and key technology of large foundation pit shaft excavation combined with anti uplift structure system to control the deformation of underground subway tunnel,which is applied to the municipal excavation of Shenzhen Qianhai Shuangjiehe Road,Tinghai road and its underground road.This engineering case verifies the reliability of the theoretical calculation method,which can provide theoretical support for similar engineering program design and construction.