Study On The Deformation Of Existing Metro Shield Tunnel In Soft Soil And The Controlling Techniques

Up to now,subway has been developed in 35 cities in China,and it has become one of most important means of transportation for people.With the continuous development and utilization of underground space,the existing subway shield tunnel under complex environment will inevitably be affected by the adjacent construction activities,resulting in hidden dangers and diseases to different extent.Since the tunnel structure is damaged,the repair would be time-consuming and the cost would be very high.Therefore,to ensure the structural safety of the shield tunnel running in soft soil area,it is of great significance to study the influence of tunnel deformation and its controlling techniques.In recent years,with the continuous development of subway construction in China,the research on deformation of tunnel structure and its control methods has gradually increased.However,the deformation evolution is affected by many factors,such as assembling mode,geological condition,construction environment and contractor's experience,etc.,that cannot be unified and standardized.The geological conditions in Hangzhou,Ningbo and Wenzhou,Zhejiang Province,are dominated by deep limnetic facies-sea facies soft soil depostion.These soft soils are characterized by high water content,high compressibility,high sensitivity,low strength and easily disturbed.As a result,the deformation and protection of shield tunnel in such soft soil layer have become an urgent topic.Based on situation,the main contents of this paper are organized as follows:(1)The distribution,classification and main engineering characteristics of soft soil in Zhejiang Province were studied.The physical and mechanical properties of soft soil in five typical regions of Zhejiang Province were obtained according to the Code for Design of Highway Embankment on Soft Ground.According to the foundation,the value of the ground resistance coefficient of the formation spring was selected.(2)The transverse calculation model of segment and bolt was established,which considering the influence of different ballast level,soil resistance and lateral pressure coefficient on tunnel deformation and the condition that the joint bolt stress reached the limit state and exited the working state.The analysis showed that the resistance coefficient was an important factor to control the development of tunnel transverse deformation.(3)The multi-contact refinement analysis model was established longitudinally in the tunnel.The longitudinal loading of tunnel is carried out step by step by taking into account the interaction between soil and tunnel.And the deformation mode and crack development of tunnel joints under longitudinal uneven settlement were studied.(4)Aiming at the deformation control measures of subway tunnels,a composite cavity reinforced shield tunnel method combing inner tension steel rings with longitudinal steel strips was proposed.The numerical calculations and analysis were performed for the different quantity arrangement of the transverse inner steel ring and the longitudinal steel strip,which verified the effectiveness of the reinforcement measures combined with the inner steel ring and the longitudinal steel strip.