Geological conditions and supporting structures are critical factors influencing the deformation characteristics of deep excavations. This study investigates the deformation characteristics and corresponding control measures for typical deep excavations, focusing on a metro station excavation within a mixed soil-rock stratum in Guangzhou. Using field measurement data collected during the excavation phase, we perform a statistical analysis to examine the relationship between maximum deformation and various influencing factors, including excavation depth, spatial effects, and the insertion ratio of the support structure. Additionally, we explore the distribution of excavation deformations, the relationship between lateral and vertical displacements, and deformation modes, offering engineering recommendations for optimization. Our analysis shows that, due to significant variations in the thickness of soft soil layers in Guangzhou, the maximum lateral displacement of the support structures predominantly ranges from 15 to 30 mm, while vertical ground deformations range from 0.86 parts per thousand to 2.35 parts per thousand of the excavation depth. Increasing the insertion ratio of the support structures improves their stiffness and reduces surface settlement caused by excavation. However, when the base of the support structure is embedded in the load-bearing rock layer and the insertion ratio exceeds 0.25, further increases in the insertion ratio lead to diminishing returns in controlling surface settlement. Both vertical ground deformations and lateral displacements of the support structures are positively correlated with excavation depth, while negatively correlated with the length-to-width ratio, width-to-depth ratio, and insertion ratio of the excavation. Based on these findings, we propose construction measures to enhance the stability of deep excavations and protect adjacent structures.

With the development of urban underground space, green and efficient excavation supporting structures are receiving increasing attention. Thus, prefabricated recyclable supporting structures (PRSSs) have been developed. A deep circular excavation supported by PRSSs in low plasticity clay (CL) was extensively instrumented to explore its deformation characteristics. The measurement results show that the lateral displacement of supporting piles (delta hp) presented a typical cumulative pattern dominated by deep inward movement. The maximum lateral displacements of supporting piles (delta hpm) varied between 0.28%H similar to 0.52%H (H is the excavation depth). The maximum lateral pile displacements mostly occurred above the excavation surface, ranging from H+0.5 to H-7.0. The soils 3 and 10 m from the excavation had the largest lateral displacement at the top and a cantilever shape. The ground surface settlements tended to follow a convex pattern. The maximum ground surface settlements (delta vm) were normalized using final excavation depth (He) on the east and south sides, i.e., 0.43% and 0.50%, respectively. The ratio of delta vm to delta hpm tends to increase as the excavation and dewatering proceeds and varies between 0.49 to 1.15. The ground surface settlement due to dewatering was 19% of the maximum settlement.

In combination with the field monitoring data, PLAXIS3D finite-element software was used to numerically model the pull-pile supporting structure in a deep foundation pit. This structure was compared to the single-row pile support structure in order to learn more about the pull-pile supporting structure's force and deformation characteristics and how it works. The study found that the cumulative horizontal displacement curves of the supporting piles are integrated into an upward convex shape. The bendingmoment curve of the front-row piles presents an inverted S shape, and the bendingmoment curve of the back-pull piles presents a bow shape. The back-pull-pile effect can improve the unbalanced distribution of positive and negative bending moments in single-row piles by changing the stress condition of the soil. In other words, the pull-pile supporting structure has good safety and serviceability and can well control the lateral displacement of the foundation pit.