Research On The Low Of Ground Settlemeng By Shield Construction Of Metro Tunnels In Soft Soil

Shield method with its unique characteristics of intelligent, safe, fast and quickly becomes a kind of important construction method of underground engineering in our country, have been extensively used in underground engineering. However, due to the inevitable shield construction will cause the surface subsidence and deformation,when the settlement is too large may endanger the surrounding buildings and the safety of underground pipelines, causing serious economic losses and social impacts,.Taking Hangzhou metro line two Zhenning Road station to station interval (outer ring road No.9shield interval) tunnel project as the project background, studied the surface by case analysis and3D numerical simulation of shield construction in subway tunnel settlement changes. The main research contents and results are as follows:(1) The shield machine before incision within30m and30m followed for shield construction within the sphere of influence of shield machine, and30m as the maininfluence range of incision, the range of the surface settlement of shield machine is more than90%; outside the incision before30m and after outside the scope of30m is not affected or influence can be neglected.(2) Shield single propulsion on surface area for the main effect of tunnel axis on both sides of the range of6m, about1times of the diameter of the tunnel; all influence area for the tunnel axis on both sides of18m, is3times of the diameter of the tunnel.(3) The surface deformation caused by the shield construction is inevitable, in front of shield machine soil disturbance is an important cause of ground settlement; in a certain geological, relative depth (H/D) and other conditions, in front of shield machineby the close relationship between the soil disturbance degree and shield the earth pressure.(4) With the increase of earth pressure, incision front ground surface uplift increased,but the increase is very small, value decreases soil surface settlement behind, andless increase a small amount is far greater than the uplift. Super equilibrium state,surface uplift values increased, surface settlement decreases, and the reduction is far greater than the increase; under balanced state, reducing the value of surface uplift,subsidence value increase, and the increase is far greater than the amount of the reduction.(5) Because of the high equilibrium surface settlement is smaller than that of under balance, the earth pressure control in the0.15MPa～0.2MPa within, as far as possible to reduce surface subsidence. Therefore, the premise in front of shield machine soil is not destroyed, appropriately increase the earth pressure is very effective measures for reducing settlement.(6) Other conditions are fixed, the surface subsidence and decreases with the increase of the pressure grouting. The grouting pressure control in the0.2MPa-0.3MPa within, to prevent the occurrence of surface subsidence of greater.