# Displacement Analyses of Main Structure of Parallel Pit Excavation and Analysis of Countermeasures
## 1 Introduction
In addition, there are a few cases of parallel foundation pit excavation with a combination of the TD method and open excavation method. In addition, besides the need to choose a reasonable construction method during the foundation pit construction, the influence of the construction sequence on the pre-existing structures should not be ignored [13]. In the face of the increasingly complex surrounding environment, the design concept of the supporting system based on a deformation-based design philosophy is adopted for the excavation of the foundation pit in the city. Therefore, a reasonable stiffness of the supporting system is essential to control the deformation and cost of the support structure. Many scholars [14; 15; 16; 17; 18] have studied the factors affecting structural deformation and surface settlement. [PERSON] et al. [17] proposed an expression for the stiffness coefficient of the support structs for the foundation excavation to assess its effect on structural deformation. [PERSON] et al. [19] established an expression that can evaluate the degree of influence of the foundation excavation on the structure by analyzing a large amount of data on the deformation of the surrounding environment caused by the foundation excavation. [PERSON] et al. [18] proposed a more suitable stiffness ratio of the support structure to evaluate the deep foundation excavation for the characteristics of the large depth of excavation and complex spatial relationship of the support structure. [PERSON] et al. [9] proposed a stiffness ratio formula that can respond to the depth of overburden and the diameter of the tunnel, which can better reflect the effect of the shield underpass on the existing pit structure. The above research cases of structural system stiffness mainly focus on the complex soil-structure interaction problem, but the influence of key factors such as staggered spacing and distance from the pit edge on the main structural system during parallel pit excavation is not fully reflected. The deep foundation pit project of the Tongzhou City Sub-center Transportation Hub in Beijing is composed of several parallel pits, which makes it difficult to co-ordinate the construction schedule and mutual interference between the pit groups; and the city road above the underground transportation hub needs to be connected as soon as possible. Therefore, the excavation of the foundation pit group cannot adopt the traditional and single construction method, and no similar foundation pit case has been found in Beijing for reference. Based on the above engineering characteristics, the advantages of the TD method and the BU method are fully absorbed; the TD method is proposed for the foundation pits below the road, and the BU method is adopted for the foundation pits on both sides of the road. By analyzing the different excavation schemes of the pits on both sides of the road and studying the deformation characteristics of the pre-existing structure in the cover excavation area, the optimal excavation scheme suitable for the project is derived. A relative stiffness coefficient \(R_{d}\) that can consider the excavation depth and distance from the pit edge is proposed, and a nonlinear curve that can consider the lateral wall displacement \(\delta_{hm}/H\) and the stiffness of the main structural system \(R_{d}\) is fitted. The results of this study can help to provide a reference for the design of supporting structs based on deformation control in Beijing.