为探究地表大面积不平衡堆载对围护结构变形的影响，以武汉市某地铁深基坑工程为研究背景，基坑东、西两侧施工红线外均存在大面积堆土。东侧大面积堆土可大致划分为①、②、③号堆土区，堆土高度分别为4~5、13~14、8.0~9.5 m，西侧堆土高度为9~13 m，东侧堆土范围显著大于西侧，为典型的地表不平衡堆载。通过建立PLAXIS 3D三维数值模型，采用考虑小应变刚度的HS-Small土体本构模型，对地铁深基坑开挖全过程进行模拟，并与现场监测数据对比验证模型的正确性； 进一步展开堆载距离和不平衡堆载情况对围护结构变形影响的敏感性分析。研究结果表明： 1）当基坑两侧存在大面积堆土时，两侧墙体呈现不对称变形特征，表现为“堆载大者变形大，堆载小者变形小”； 2）紧邻端头井的墙体变形受空间效应主导，显著大于地表堆载影响； 3）堆载距离与墙体侧移呈负相关，距离越近影响越显著； 4）当移除基坑一侧堆土时，本侧墙体侧移减小，但导致对侧墙体侧移显著增加，不能确保基坑变形均在预警值范围以内。
To explore the influence of large-area unbalanced surface surcharge on the deformation of retaining structures, a case study is conducted on a metro deep foundation pit project in Wuhan with large-area soil piles distributed outside the construction red lines on both the eastern and western sides. The eastern soil piles are divided into Zones 1, 2, and 3 with heights of 4－5 m, 13－14 m and 8.0－9.5 m respectively, and the height of western soil piles ranges from 9－13 m. The coverage range of eastern soil piles is obviously larger than that of the western side, forming a typical form of surface unbalanced surcharge. A three-dimensional numerical model based on PLAXIS 3D is established, and the constitutive hardening soil model with small-strain stiffness is adopted to simulate the whole excavation process of the metro deep foundation pit. The reliability of the numerical model is verified by comparing with field monitoring data. Furthermore, sensitivity analyses are carried out to discuss the influences of surcharge distance and unbalanced surcharge condition on retaining structure deformation. The research conclusions are drawn as follows: (1) Large-area surcharges on both sides of the pit cause asymmetric deformation of retaining walls, namely larger deformation occurs at positions with greater surcharge and smaller deformation at positions with less surcharge. (2) The deformation of retaining walls adjacent to end shafts is dominated by spatial effect, which exerts a more prominent influence than surface surcharge. (3) The surcharge distance is negatively correlated with the lateral displacement of retaining walls, and the influence becomes more significant with the decrease of distance. (4) Removing the surcharge on one side of the pit can reduce the lateral displacement of retaining walls on the same side, but will lead to a remarkable increase in the displacement of the opposite side, which fails to guarantee all pit deformation values within the early warning range.
