# Study on the Disturbance of Existing Subway Tunnels by Foundation Sloping Excavation
###### Abstract
[10] used the MIDAS/GTS software to establish a finite element model to evaluate the effect of excavation in different sections of the pit on the tunnel deformation. [PERSON] et al. [11] developed a numerical model to analyze the tunnel deformation caused by the excavation of the circular pit. [PERSON] et al. [12] introduced a deep foundation pit excavation project, which provides a complete description of the deep excavation behavior through a complete monitoring system. [PERSON] [13] introduced the disturbance of a deep foundation pit excavation to the surrounding buildings and existing subway tunnels; [PERSON] et al. [14] used a three-dimensional numerical calculation software to analyze the response of the excavation sequence of the foundation pit to the surrounding brick masonry wall during excavation. A large number of scholars have carried out studies on the disturbance caused by the excavation of the foundation pit to the adjacent tunnel. Among them, the theoretical analysis method has been widely used to predict the disturbance caused by foundation excavation to the neighboring structures with high prediction efficiency, high applicability and reliable accuracy [15; 16; 17]. Sloping excavation is an excavation method that can effectively reduce the magnitude of one-time excavation unloading load of the foundation pit and maintain the stability of the surrounding environment of the foundation pit. In the existing foundation excavation project, the block excavation method is often used. After the excavation of the soil, load backpressure is often applied in order to reduce the disturbance of the subterranean tunnel under the foundation pit in a one-time excavation. This results in a complicated and uneconomical construction process. Compared with the commonly used block excavation method, the sloping excavation can reduce the disturbance of the excavation to the underlying tunnel by using the unexcavated slope as the backpressure load after excavation. However, in the available research, only the overall block excavation is usually considered, and there is a gap in the research on the use of a sloping excavation method for foundation pits. With the increasing number of urban foundation pit projects, it is important to propose corresponding analytical prediction models and the formulae to clarify the disturbance effect on existing tunnels by using the sloping excavation method for foundation pits. Our study is based on the background of the channel across the river over Changsha Metro Line 1 at XiangYa Road, Changsha, Hunan Province, China. The two-stage method is used to derive the theoretical calculation formulae for the deformation of existing tunnels triggered by the foundation pit sloping excavation (method of excavating the middle soil and reserving core soil on both sides, method of excavating on both sides soil and reserving the middle core soil). The numerical calculation model is constructed in order to verify the correctness of the theoretical calculation formula and results. Finally, the effects of different slope footings, different slope widths and different excavation depths on the deformation of existing tunnels are analyzed. Finally, our paper aims to formulate a theoretical foundation for the analysis of the disturbance of the excavation.