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.