Comparative investigation on deformation monitoring and numerical simulation of the deepest excavation in Beijing

The investigation on the mechanical mechanism of the retaining and protection structure of superdeep excavations is an important subject, and its deformation control research is particularly important. Taking the deepest foundation pit with full-section overall excavation in Beijing as an example, this paper studies the stress and deformation characteristics of composite soil nailing wall and anchored soldier pile wall combined retaining system under complex geological conditions of multi-layer groundwater during the process of excavating 31.4 m deep. The Midas simulation software and monitoring data are used to analyze the construction process of foundation excavation. The simulated results and monitored values of anchor force, ground settlement, and soil deformation during foundation excavation are analyzed and discussed to verify the reliability of the model. The spatial effect of internal force and deformation of composite retaining and protection structure for superdeep foundation excavation is discussed, and the parameters affecting the retaining structure are analyzed and investigated. The research shows that with the increase of excavation depth, both the extremum of the bending moment and the extremum of lateral displacement of retaining piles are increasing, and the position of the extremum of bending moment is located near the excavation face; then, the bending moment reaches the maximum when the foundation pit is excavated to the bottom. Within a certain range, increasing the rigidity or the embedded depth of the retaining pile or the prestress of the anchor can effectively control the lateral displacement of the excavation. However, when the rigidity of retaining pile is too large, its lateral displacement does not change significantly. Similarly, when the embedded depth is too long or the prestress of the anchor is too powerful, the effect of controlling deformation is also not obvious. The research results will provide theoretical basis and practical experience for the design and construction of superdeep excavations.