Soil Deformation Caused By Epb Shield Tunnelling In Sandy Cobble Stratum And Control Measures

Sandy cobble stratum is a typical mechanical unstable layer, the mechanical properties and physical properties of the stratum much differ from soft soil, loess and composite stratum greatly. Gravel particles of sandy cobble stratum passes force point-to-point under waterless status and the stratum responses sensitively after being disturbed. In the stratum, rock masses are loose,noncemented and bad self-stable, strenghth of single rock is high; the interspace is wide and the permeability coefficient is large. It is rare in the world and firstly tunnelled in such stratum in China, the similar stratum can be found in Taipei metro, Torino metro, Japan metro and water conveyance tunnel. When the Earth Pressure Blance shield tunnelling in long and large-area sandy cobble stratum, it will meet many problems, such as large surface settlement, low tunnelling efficiency, residual soil with bad fluidity, shield cutters with severe wear and difficult to control stability of excavation face. From the shield contructions in domestic and overseas, we can find that ground movement and deformation regularity caused by soft soil tunnelling are thorough researched, construction disturbance of composite stratum and loess stratum are also researched extensively, but the deformation regularity and control measures of shield construction in sandy cobble stratum are researched rarely . Particularity and regionality of the stratum result in no ripe theory about soil deformation and settlement regularity of sandy cobble stratum can be referenced.Based on the background of three intervals from Renmin north road to Tianfu square on the NO.2 label of the Chengdu Metro line1, the thesis anlyzed influence factors of the soil deformation when the shield tunnelling in the sandy cobble stratum , summerization of formation characteristics and settlement regularity of main metro cities in domestic. Studied on the collapse process of excavation face when the shield tunnelling in the sandy cobble stratum and stress distribution in the chamber under three conditions by discrete element software-PFC; studied on the settlement regularity when the EPB tunnelling under conditions of different tunnelling pressure, different thickness of equivalent circle zone, different thickness of covering soil and different clear distance and analyzed the settlement process and influence scope by constructing three-dimension numerical model based on finite element software-ANSYS. Grasped regulary problems wholely and proposed suggestions for control parameters. Finally, analyzed main tunnelling parameters such as tunnelling velocity, grouting pressure, thrust force of the jack and the relationship between chamber pressure of the NO.3 stress point with surface settlement based on the project examples. Took the Wanfu Bridge for example, the thesis studied on the control measures for decreasing ground disturbance,grouting and improving cutters adapatability of crossing construction. Wishing the analysis results could provide basis for further similar tunnelling design and construction to create social benefits and economic benefits.