## 1 Introduction
A study in the literature [17] examined a preloading technique to analyze the load-displacement behavior of piles, the interaction between piles and soil during preloading, and the extra load induced by vertical extension through centrifugal testing. [PERSON] et al. [18] used the shield tunnel project of the Xi'an Subway as a case study. The bearing capacity of a single pile and the deformation of a joint were calculated based on their structural design. The calculation of the bearing capacity indicates that the reinforcement of the pile foundation is feasible. [PERSON] et al. [19] examined the process of excavating a foundation pit beneath the bridge floor, as well as the use of a direct shield tunneling machine to cut through the raft bottom pile and pile during the building of the Shanghai Metro Line 10 tunnel. They also analyzed the mechanism by which the load is transferred within the bridge structure. It has been determined that the removal of the original piles has minimal impact on the bridge structure during excavation. [PERSON] [20] conducted research on pile foundation underpinning to control building deformation and integrated it with foundation pit support to provide a comprehensive set of important technologies for developing underground spaces directly beneath cultural relic buildings. [PERSON] [21] examined the alterations in the placement of pile foundations during the process of underpinning. The study discovered that increasing the thickness of grouting reinforcing rings can successfully reduce soil disturbance around the piles and manage the settlement of the pile foundation. Minimizing excavation steps can also reduce soil disturbance around the piles and enhance the stress status of the pile foundation throughout the underlying process. [PERSON] [22] depends on a comprehensive pipe corridor foundation pit that is located next to the ongoing expressway bridge project. The study demonstrated that the excavation of a deep foundation pit will result in increased deformation and internal force in the piling foundation of the nearby highway bridge. [PERSON] et al. (2018) investigated the possibility of using passive underpinning technology in a pile foundation underpinning project with significant axial force. They conducted their study on an undercrossing viaduct in a foundation pit in Wuhan. The researchers examined the deformation characteristics of both the structure and the foundation pit under various processes. [PERSON] (2018) provided a concise overview of the main control technologies used for pile foundation underpinning in the context of the Dongxin Expressway bridge underpinning project beneath a subway tunnel in Guangzhou. The current research on deep foundation pit construction reveals that most studies have focused on the impact of deep foundation pits on the surrounding environment and existing bridge structures. However, there is a lack of research on the influence of road deep foundation pits adjacent to or undercrossing bridges. Thus, it is crucial to analyze the engineering characteristics of a road deep foundation pit in Beijing that utilizes pile foundation underpinning technology to pass beneath an existing subway viaduct project. This study focuses on summarizing the key technologies involved, such as the simultaneous replacement of five bridge foundations, the replacement of a large number of new piles, the replacement of a large span of abutment, the construction of a long, deep foundation pit for the road, and the wide range of influence. Additionally, this study aims to investigate the impact of pile foundation underpinning and road foundation pit construction on the existing bridge and track structure. Additionally, references for similar work can also be provided.