关键词: 变形预测, 扰动影响范围, 剪切位移法, 修正剑桥模型, 盾构施工

Abstract: Accurate prediction of ground deformation and its influence range based on the elastic-plastic stress-strain relationship of soil during and after shield tunnelling has important theoretical significance and engineering application value. On the basis of deducing the scope of plastic loosening zone of surrounding soil, this paper puts forward the conclusion that the angle between plane segment and horizontal plane of composite sliding surface produced during shield tunnelling and after leaving is 45°?φ/2 and 45°+φ/2 (φ is internal friction angle), respectively. The formula of safety factor Fs for the composite sliding surface in soil under both active and passive states is proposed. Moreover, the possible sliding surface is ascertained by the random search method, and the influence range of lateral disturbance in shield tunnelling and departure stage is quantitatively determined. In shield tunnelling, the surface uplift is caused by the shear displacement of the soil on top of the shield. The shear displacement formula is deduced to predict the surface uplift by controlling stress τ1, τ2, τ3 and the shear modulus Ge, Gp1, Gp2 at different stages in the direct shear test curve, as well as controlling stress τ1, τ2, τm and corresponding distances l1, l2, lm according to the τ-l curve. After the shield is removed, the ground settlement is caused by the consolidation of the soil resulted from the dissipation of negative excess pore water pressure responding to the soil unloading on top the shield. The shear strain of the soil according to the modified Cambridge model is used to predict the settlement. Taking Wuhan River-crossing Tunnel as an engineering case, the influence range of surface deformation, heave and settlement are calculated quantitatively. It is concluded that the influence range of transverse disturbance and heave of surface at different construction stages of shield tunnelling are in good agreement with the measured values, and the predicted value of unloading settlement is in accordance with the measured value of the total settlement.

Key words: deformation prediction, disturbance influence range, shear displacement method, modified Cam-clay model, shield tunnelling