Analysis of Temporal and Spatial Characteristics and Influencing Factors of Construction Deformation of Super-Large Deep Foundation Pit in Thick Sand Stratum

To the aim of this paper is to study the structural and environmental deformation characteristics caused by the excavation of a very large deep foundation pit in the sandy soil area of Beijing. This paper is based on numerical simulation and field monitoring results and these results are compared with the deformation data of a soft soil foundation pit in the Shanghai area. The results show that the influence of the environment surrounding the super-large deep foundation pit project studied in this paper is obviously too great. With the progress of construction, the deformation rate and deformation amount of the column at the side of the foundation pit are obviously higher than that of the column in the middle area. Due to the “hysteresis” of stress transfer in the sand, the settlement of the roof of the north wall is delayed and the deformation range is smaller than that of the south wall. Compared with the conventional foundation pit, the influence area of the surrounding surface is larger, reaching 4 He (He is the depth of the foundation pit). Δvmax (the maximum surface settlement) is between 0.2~2.3% He, and the relationship between δvmax = 1.43% Vwm. Through orthogonal experiments and numerical simulation, it is concluded that the deformation of foundation pit structure and its surrounding environment is more sensitive to excavation unloading, precipitation amplitude, and column spacing. It is also concluded that the strong, medium, and weak influence areas of the bottom uplift after foundation pit construction are (0~0.07) × L, (0.07~0.14) × L, and (0.14~0.5) × L, respectively (L is the width of foundation pit). When the embedment ratio is between 1.8~2.4, the displacement mode of the parapet structure is T mode; when the embedment ratio is between 2.4~3.4, the displacement mode of the parapet structure is RB mode.