## 6 Conclusions  
Considering the soft soil feature of the aviation oil pipeline adjacent to the Xinxingcun Station of Tianjin Metro Line 4 in China, this paper compared and analyzed the differences in the impact of layered excavation and step excavation on the adjacent pipeline through Midas numerical simulation, and then discussed the impacts of foundation excavation on the pipeline-soil gap, before comparing the numerical simulation results with the measured data. Lastly, this paper discussed the influence of changes in the pipeline foundation and underlying soil layer on the settlement of the pipeline. The main conclusions are drawn as follows:  
(1) The layered excavation method has better control over horizontal displacement and settlement of pipelines than the bench excavation method. During the excavation process, the maximum vertical settlement of the aviation oil pipeline caused by layered excavation and bench excavation was 8.1 mm and 12.5 mm, and the latter was 54.3% more than the former. The settlement of pipeline tended to be large in the middle and small at the ends, regardless of the bench excavation method or layered excavation method.  
(2) Excavation of the foundation pit can cause the pipeline near the foundation pit to partially separate from the surrounding soil. Cracks occurred in the vertical direction of the pipeline after the construction of the foundation pit support structure. In the process of foundation pit excavation, the pipeline-soil gap changed from an open state to a squeeze state at the angles of 25\({}^{\circ}\) and 205\({}^{\circ}\) to the pipeline. When excavation was completed, the soil was squeezed to the maximum at the angles of 110\({}^{\circ}\) and 205\({}^{\circ}\) to the pipeline, the pipeline-soil gap changes from a squeeze state to an open state, and the pipeline-soil gap reached its maximum value of 2.3 mm.  
(3) With the advance of the construction stage, the vertical settlement of GXC-03, GXC-08, and GXC-10 measuring points gradually decreased, the settlement value of GXC-13 point tended to be stable, and the settlement value of the GXC-16 and GX-21 measuring points showed an upward trend. The comparison of the monitoring data showed that the numerical simulation results were basically consistent with the field measurement data. Therefore, it is proper and feasible to use the layered excavation method for the foundation pit excavation of Xinxingcun Station.  
(4) The comparison of different soil layer properties showed that layered excavation had a better effect on controlling pipeline settlement than bench excavation. In the event that the soil layer where the pipeline is located is of high compressibility and de  
Figure 20: Comparison of pipeline settlement with different soil layer properties. (**a**) Layered excavation; (**b**) Bench excavation.  
formation, the layered excavation method is the first choice. Otherwise, it is necessary to grasp the key points in station construction and comprehensively select an appropriate construction method.  
Conceptualization, Z.S.; Methodology, Z.S., Y.Z. and K.W.; Software, Z.S., Y.W., J.T. and X.T.; Validation, Y.W. and X.T.; Formal analysis, Z.S. and Y.Z.; Investigation, Y.W., K.W. and J.T.; Data curation, Y.W.; Writing--original draft, Z.S., Y.W., K.W. and J.T.; Writing--review & editing, Y.Z.; Visualization, Y.Z.; Supervision, Y.Z. and X.T.; Project administration, Z.S. and Y.Z.; Funding acquisition, Z.S. All authors have read and agreed to the published version of the manuscript.  
This study would not have been possible without financial supports from the Science and Technology Innovation Team of Shaanxi Innovation Capability Support Plan (No. 2020 TD005), and Shaanxi Province Housing and Rural Construction Science and Technology Plan (No. 2019-K39), and General Project of Shaanxi Natural Science Basic Research Program (2023-JC-YB-297).  
Not applicable.  
All data and models generated or used during the study are available from the corresponding author by request.  
The authors declare no conflict of interest.