盾构施工中土体损失引起的地面沉降预测

土质软硬决定了隧道周围土体的移动方向,移动焦点在隧道中心点与隧道底部位置之间变动。采用两圆相切的土体损失模型,通过引入移动焦点的坐标参数,建立了统一的土体移动模型,该模型能将Park模型与Loganathan模型包括在内。假定土体不排水,利用源汇法推导了由土体损失引起的地面沉降通用计算公式,该方法适用于施工阶段。算例分析表明该方法的计算结果与实测值非常吻合,适用于各种土质条件。Loganathan公式只适用于土质较差的情况,当土质较好时计算得到的地面沉降量要比实测值偏小。

Prediction of surface settlement induced by ground loss during shield tunneling construction

Ground movement pattern of shield tunnel is investigated. It is put forward that the direction of ground movement is conditioned by soil type, and the novel parameter “movement focus” alters its site between center and bottom of tunnel. Ground loss model of tangent double circles is adopted to establish a uniform ground movement pattern of shield tunnel by introducing the coordinate parameter of movement focus. This novel pattern includes Park pattern and Loganathan pattern. Assuming soil is undrained, the general calculation formula for surface settlement induced by ground loss is deduced with virtual image method. This method is applied to the construction phase. As shown in analytical calculation, the predicted surface settlements are in good agreement with the observed settlement; and this method is applicable for all different soil conditions. Loganathan’s formula only fit for bad soil condition. The predicted surface settlements for good soil condition are smaller than the observed settlements.