盾构掘进、离开施工阶段对地表变形的影响范围及量化预测

Influence range and quantitative prediction of surface deformation during shield tunnelling and exiting stages

针对盾构掘进中、离开后施工阶段,依据土体弹塑性应力-应变关系进行分析,准确预测地表变形量及影响范围具有重要的理论意义和工程应用价值。在导出隧道周围土体塑性松动圈范围的基础上,提出了盾构掘进中、离开后土体内产生的复合滑动面平面段与水平面夹角分别成45°-φ/2和45°+φ/2(φ为内摩擦角)的结论,推导了土体呈主动、被动状态复合滑动面安全系数Fs公式,并利用随机搜索法,找出可能的滑动面,量化确定盾构掘进、离开阶段横向扰动影响范围。盾构掘进中,地表隆起因盾构上部土体发生剪切位移引起,通过直剪试验曲线中控制应力τ1、τ2、τ3及不同阶段剪切模量Ge、Gp1、Gp2,并依据τ-l曲线控制应力τ1、τ2、τm及相对应的距离l1、l2、lm。推导出剪切位移公式,预测地表隆起量;盾构离开后,地表沉降由盾构上部土体卸荷产生的负超孔隙水压力消散引起土体固结所致,应用修正剑桥模型中土体剪切应变预测沉降量。以武汉过江隧道为工程案例,对地表变形影响范围及隆沉量进行量化计算,得出盾构不同施工阶段横向扰动影响范围、地表隆起量与工程实测值吻合较好,卸荷沉降预测值与总沉降实测值趋势一致。

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(φis 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 stressτ1,τ2,τ3 and the shear modulus Ge,Gp1,Gp2 at different stages in the direct shear test curve,as well as controlling stressτ1,τ2,τm and corresponding distances l1,l2,lm according to theτ-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.