# Influence of Deep Foundation Pit Excavation on Adjacent Pipelines: A Case Study in Nanjing, China
## 6 Conclusions  
This study investigated the impact of deep foundation pit excavation on neighboring pipelines in a floodplain area in Nanjing, China. In this study, the issue of long-term pipeline deformation due to deep foundation pit excavation was analyzed with a focus on its progression over time. It addressed how the excavation process influences the mechanical properties of the surrounding soil, resulting in the gradual deformation of nearby pipelines. This paper emphasized the need for continuous monitoring and evaluation of pipeline integrity over time, as immediate effects may be minimal, but long-term effects can be significant, potentially leading to pipeline damage or failure if not properly managed. The focus was on three main factors: the distance between the pipeline and the foundation pit, the pipeline burial depth, and the depth of pit excavation. Using relative sensitivity analysis, this research quantified the extent to which each factor influences pipeline deformation. The main conclusions can be drawn as follows:  
1. After the completion of foundation pit excavation, the pipeline typically exhibited a concave shape, with greater settlement in the middle and lesser settlement at the ends. Uneven displacement of the pipeline primarily occurred within 1.6 times the excavation length near the pit corners. It is recommended that the pipelines near the pit corners be specially protected prior to excavation to prevent uneven settlement, which could lead to tearing or rupture of the pipelines. 2. With an increase in the depth of the pit excavation, both vertical and horizontal displacements of the pipeline increased, with a relatively larger increase occurring in vertical displacement. Compared to excavation in a single-soil layer, excavation in composite soil-rock strata showed a relatively smaller impact on the settlement deformation of adjacent pipelines. 3. As the distance between the pipeline and the pit increased, both vertical and horizontal displacements of the pipeline gradually decreased. When the distance between the pipeline and the pit was less than 1.2 times the depth of excavation, larger uneven displacements of the pipeline were observed. This calls for careful planning and monitoring of pipeline integrity in close proximity to excavation sites. 4. Both vertical and horizontal displacements of the pipeline decreased with an increase in the depth of pipeline burial. To prevent significant uneven displacement and potential damage to pipelines due to pit excavation, the burial depth of the pipelines should be no less than 5 m. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Influencing Factors** & \
\begin{tabular}{c} **Vertical Displacement** \\ **Sensitivity** \\ \end{tabular} &
\begin{tabular}{c} **Horizontal Displacement** \\ **Sensitivity** \\ \end{tabular} \\ \hline Depth of pit excavation & 0.198 & 0.156 \\ Distance between pipeline and pit & 0.455 & 0.655 \\ Depth of buried pipeline & 0.412 & 0.325 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Sensitivity of each factor to pipeline displacement. 5. The analysis indicated that the distance between the pipeline and the pit is the most critical factor influencing deformation, followed by burial depth. This underscores the need for the strategic planning and placement of pipelines in relation to excavation activities. B.W. : investigation, writing--original draft, funding acquisition; C.G. : software, formal analysis; P.L. : funding acquisition, writing--review and editing; M.Y. : data curation; L.L. : visualization. All authors have read and agreed to the published version of the manuscript. The authors gratefully acknowledge the financial support provided by Science and Technology Funding Scheme for Three Companies of China Construction Bureau II No. CSCEC2b3c-2021-K-65. Not applicable. The data presented in this study are available in this article. Author [PERSON] was employed by The Third Construction Engineering Company Ltd. of China Construction Second Engineering Bureau.