MECHANISMS AND ANALYTICAL SOLUTIONS FOR SOFT-GROUND DEFORMATION INDUCED BY SHIELD TUNNELING

Shield tunneling in soft ground can induce pronounced ground surface settlement, posing a potential risk to adjacent infrastructure. Although shield-induced settlement has been extensively investigated through field monitoring and numerical simulation, mechanics-based analytical studies with systematic validation remain relatively limited. In this study, the ground deformation induced by shield tunneling is decomposed into four components: shield thrust-induced settlement(w_q), shield-soil friction-induced settlement(w_f), ground loss-induced settlement(w_v), and synchronous grouting-induced deformation(w_p).Based on Mindlin's and Sagaseta's solutions, analytical expressions for these settlement components are derived in local coordinate systems, transformed into a global coordinate system, and subsequently superimposed to establish an analytical model for predicting shield tunneling-induced surface settlement. Parametric analyses are then performed by considering tunnel burial depth and ground loss as the controlling variables. The results indicate that(w_q), (w_f), and(w_vp), where w_vp denotes the combined contribution of ground loss and synchronous grouting, account for approximately 3% ~6%, 5% ~7%, and 80% ~90% of the total settlement w, respectively. Both w_q and w_vp decrease with increasing tunnel burial depth H, whereas w_f shows an increasing trend. The total surface settlement w exhibits a negative exponential relationship with H; specifically, when H decreases from 18 m to 6 m, w increases by 76.5%.Over-excavation has a limited influence on the spatial distribution of w and its individual components but significantly affects their magnitudes. A strong linear relationship is observed between the total settlement w and the excavation radius R; when R increases from 3.2 m to 3.5 m, the total settlement increases by 156%.This study provides a mechanics-based analytical framework for quantifying the contribution of different shield tunneling processes to surface settlement and offers theoretical support for settlement prediction and deformation control in soft-ground tunneling. The findings of this study provide a data foundation and computational basis for the design of metro tunnels in soft soil formations and the control of shield construction parameters, particularly for shield construction in shallow-buried tunnels.