Spatiotemporal deformation patterns induced by ultradeep excavation in soft soil areas

The rapid development of underground space in soft soil areas necessitates improved understanding of the deformation patterns and mechanisms associated with ultradeep excavations. This study investigated the spatiotemporal deformation patterns induced by a 34.9 m-deep subway station excavation in Tianjin, China, constructed using the top-down (TD) method. The difference in deformation patterns between excavations using the bottom-up (BU) method and those using the TD method is discussed through field measurements and numerical simulations. In TD excavation, the magnitude of diaphragm wall (DW) horizontal displacement is significantly smaller than that in BU excavation. Furthermore, the rate at which the depth of maximum horizontal displacement increases with excavation depth is slower than that observed in BU excavation. Under stratum heave effects, the DW exhibited an uplift of up to 20 mm, generating differential displacements exceeding 10 mm between the wall and column. Stratum heave further exacerbated the differential settlement of adjacent buildings, causing the far-side foundation to experience uplift while settlement persisted on the near side. After accounting for wall uplift, the ratio of the maximum ground surface settlement to maximum lateral wall displacement ranged from 0.4 to 2.0, consistent with previous studies. The progressive development of DW deformation in both horizontal and vertical directions was summarized. The growth curve of TD excavations exhibits a convex upward shape, whereas that of BU excavations exhibits a convex downward shape. These findings provide guidance for the stage-specific deformation control of comparable complex projects in soft soil areas and highlight the need to incorporate stratum heave effects into the deformation analysis and structural design of ultradeep excavation support systems.