超深基坑水下开挖三维数值模拟研究——以上海吴淞口长江隧道工程为例

Three-Dimensional Numerical Simulation of Underwater Excavation in Ultra-Deep Foundation Pits—A Case Study of the Shanghai Wusongkou Yangtze River Tunnel Project

摘要: 随着城市地下空间开发的深入，超深基坑在富水软土地区日益增多，其施工面临着变形控制和稳定性等问题。本文依托上海吴淞口长江隧道浦西接收井的超深基坑，采用三维有限元数值模拟方法对基坑水下开挖结合逆作法施工的全过程进行了模拟。模拟结果表明：1) 水下开挖时坑内水体形成的静水压力有效平衡了部分坑外水土压力，最大侧向位移仅为28 mm，变形控制效果良好。2) 开挖至坑底时因卸荷导致的最大隆起量约为10 mm，有效抑制了坑底土体的过大回弹。3) 坑内疏干后素混凝土底板最大上浮量约为10 mm，最大Mises应力为0.118 MPa，远低于C30混凝土的设计强度。4) 抗拔桩受力分布呈现“中间小、两边大”的特点，最大拉力为2332 kN，小于单桩承载力设计值2747 kN。研究结果验证了该超深基坑水下开挖方案的可行性。

Abstract: With the continuous expansion of urban underground space development, the number of ultra-deep foundation pits in water-rich soft soil areas has been increasing, posing challenges in deformation control and overall stability. This study focuses on the ultra-deep foundation pit of the reception shaft on the Puxi side of the Wusongkou Yangtze River Tunnel in Shanghai, where a three-dimensional finite element numerical simulation was carried out to model the entire process of underwater excavation combined with the top-down construction method. The results showed that: 1) the hydrostatic pressure inside the pit during underwater excavation effectively counterbalanced part of the external earth and water pressures, limiting the maximum lateral displacement to only 28 mm with satisfactory deformation control; 2) when excavation reached the pit bottom, unloading induced a maximum heacve of about 10 mm, effectively suppressing excessive rebound of the subsoil; 3) after dewatering, the plain concrete base slab exhibited a maximum uplift of approximately 10 mm and a maximum Mises stress of 0.118 MPa, which is far below the design strength of C30 concrete; 4) the uplift-resisting piles showed a load distribution characterized by “smaller in the middle and larger at the edges,” with a maximum tensile force of 2332 kN, lower than the designed ultimate pile capacity of 2747 kN. These findings confirm the feasibility of the proposed underwater excavation scheme for ultra-deep foundation pits.