Study On Stability Of Tunnel Excavation Face For Shield Machine In Complex Ground Under Facing Slope Conditions

With the rapid growth of China's economy, the construction of city all over the country is underway. The existing traffic in many areas has been unable to meet the needs of modern city. To solve the increasingly serious problem of traffic congestion of the city effectively, subterranean traffic has become a hot issue of common concern in academic circles and engineering. Shield technology has been widely used in subway construction for it's construction speed and low labor intensity. But in engineering practice, many complicated engineering problems is to be solved. To find the economic and secure method of Construction, the engineers and scholars need to be engaged.Due to the effect of slope of the line and of composite formation conditions, it is more difficult to control the supporting force of excavation face of shield tunnel compared with the general situation. If the force is not applied properly, it could lead to the collapse of tunnel, surface subsidence and other Engineering accident. Based on this reason, This paper intends to Analysis the stability of excavation face of shield tunnel under the slope of the line and of composite formation conditions, to guide the engineering practice.First of all, this paper use the finite element software ABAQUS simulate excavation of shield tunnel. Compared the calculation results with the reference value, it could verify the feasibility of the method. Then this paper use this software to establish numerical model of shield tunnel under the slope of the line and of composite formation conditions, to analysis the stability of the excavation face. It get the nephogram of displacement of soil in front of excavation face of shield tunnel under different supporting pressuce. Combined with previous research, the paper get the shield tunnel excavation face the value of limit supporting pressure. Then it analysis the law of surface subsidence when the excavation of the tunnel. the horizontal displacement and vertical settlement increase in front of thr shield tunnel excavation face when the supporting pressuce decrease. At the same time, the scope of influence is more broad. But the scope of horizontal displacement is more than the horizontal settlement. The influence range of vertical settlement has been extended to the surface of the earth when the excavation face failure. The influence range of horizontal displacement is only in front of the excavation face. At last, it analysis the related arameter.Secondly, For the status quo that there are few reseachs about the limit supporting force of tunnel excavation face for shield machine in complex ground under the slope of the line conditions, based on the limit equilibrium method, silo theory and hypothesis of sliding surface is broken line, the limit supporting force calculation model and formula of excavation face for shield tunnel in complex ground under the slope of the line conditions is established. Analysis of the effect of buried depth,thickness of upper and lower soil layer, slope, cohesion and internal friction angle on limit support force are given. It shows that the results are different considering the slope of the line and layered or not when the layer is uneven. Therefore, it can not be equated with homogeneous soil and Flat conditions, which should be considered in engineering practice.Finally, these two methods are used in a project example, which proved the correctness of the proposed method.