## 4 Field Test and Validation
### Soil Settlement at the Top of Pipeline  
As shown in Figure 17, the settlement caused by the construction of the support structure was taken as the initial settlement, and the numerical analysis results were compared with the actual measured results. Since it was impossible to consider all factors in the numerical analysis, the actual measured results were different from, i.e., lower than, the numerical results to some extent. In terms of the variation trend, the actual measured results were similar to the numerical analysis results, indicating that the numerical analysis results were of high reliability. It can be seen from the figure that, with the advance of the construction stage, the vertical settlement of GXC-03, GXC-08, and GXC-10 measuring points gradually decreases, the settlement value of the GXC-03 point tended to be stable, and the settlement value of the GXC-16 or GXC-21 measuring point showed an upward trend, mainly attributable to the difference in distance between the pipeline and foundation pit. [PERSON] et al. [29] divided the settlement area of surrounding soil caused by foundation pit excavation into two parts, i.e., the major influence area and secondary influence area, with a critical value \(y_{0}/H_{\text{e}}\) in the middle (\(y\) is the length from foundation pit support, and \(H_{\text{e}}\) is the depth of foundation pit). A lower \(y/H_{\text{e}}\) than the critical value indicates a large soil settlement and obvious change in settlement; a higher \(y/H_{\text{e}}\) than the critical value represents a small soil settlement and slow change in settlement. Figure 18 shows the settlement cross-section at the center of the model. The soil 15 m outside the foundation pit was the major influence area, where the settlement of the earth surface gradually decreased with the increase in excavation depth. The soil beyond 15 m was the secondary influence area, where the surface settlement increased with the increase in excavation depth. Figure 17: Comparison of vertical settlement of measuring points. (**a**) GXC-03; (**b**) GXC-08; (**c**) GXC-10; (**d**) GXC-13; (**e**) GXC-16; (**f**) GXC-21. For GXC-08, the nearest measuring point to the edge of foundation pit, the maximum settlement of soil at the top of the pipeline was 14.14 mm according to numerical simulation, the change in settlement was 7.55 mm during excavation, and the settlement arising from excavation at each layer accounted for 13.2%, 31.3%, 27.7%, and 27.8% of the total settlement. In actual excavation, the maximum settlement of soil at the top of the pipeline was 14.27 mm, and the change in actual settlement was 5.81 mm, and the change in settlement for each soil layer was 2.01 mm, 2.42 mm, 0.59 mm, and 0.79 mm, accounting for 34.6%, 41.6%, 10.2%, and 13.6% of the total settlement, respectively. The settlement variation range caused by the excavation of the first and second soil layers accounted for three-fourths of the total settlement, revealing that the initial excavation of soil caused a great disturbance to the adjacent area. For GXC-21, a measuring point far away from the foundation pit, the maximum settlement of soil at the top of the pipeline was 5.70 mm according to the actual measurement, and the overall settlement variation range was 2.12 mm. The maximum settlement was 4.80 mm according to simulation, and the overall settlement variation range was 1.56 mm during excavation. It can be seen that the distance between the pipeline and foundation pit was negatively correlated with the settlement of soil at the top of the pipeline. By comparing the actual measured data and numerical analysis results of horizontal displacement and settlement at each monitoring point, it can be found that, due to some assumptions made in the numerical modeling, the variation trend of the numerical simulation results was relatively simple, while the field measured data fluctuated greatly with the foundation pit excavation, such as at the measuring points TST-1, GXC-10, and GXC-13.