It is an effective approach to use Steel Tube Slab (STS) structure combined with the Pile-Beam-Arch (PBA) method to construct a large-space underground station. Traditional construction methods cannot meet the requirement of construction because of the complicated soil layers and high building densities in urban areas. The STS method can effectively increase the rigidity of the supporting system by using steel tubes. Firstly, the stress of bolts and steel tubes are investigated in the construction process based on the field monitoring data. Subsequently, FLAC3D is used to establish a three-dimensional model, which is verified based on the in-situ monitoring data; the effect of excavation process on ground settlement, deformation of STS structure and bridge pile are studied by numerical results. Moreover, the key parameters such as welding of flanges and the step length are studied. The results show that the stress of the steel tubes and flanges does not exceed the designed strength during the construction process. Based on the numerical simulation data, it is indicated that the STS structure can be a very effective and dependable measure in controlling and reducing the surface settlement and the existing adjacent buildings. The numerical results can be used to guide the later construction.

The excavation of a foundation pit will break the original stress balance and affect the surface settlement of the natural foundation of adjacent buildings, so deformation control is very important. In this paper, numerical simulation results of the additional stress of a natural foundation caused by a foundation pit excavation were compared with experimental results to verify the accuracy of the numerical model of a foundation pit excavation and obtain a reliable ratio of building width to the average particle size of the sand that was not affected by the particle size effect. Then, the distribution and variation law of the surface settlement of a natural foundation caused by excavation was studied by a model test, and the relationship between the deformation of a natural foundation and the depth of a foundation pit excavation and the additional load of building was obtained.

Existing railways can no longer meet transportation requirements, and it is an urgent need to expand old tunnels. However, the existence of ventilations shaft makes expansions face greater risks. This study analyzed the tangential stress change trend during the expansion process through field monitoring, and numerical simulation was used to analyze the changes in stress and displacement under different shaft depths and width–span ratios. The results show that as one approaches the tunnel face, the tangential stress in the arch foot and side wall of the J-2 and J-3 sections gradually increased, and the tangential stress in the arch foot and side wall of the J-1 section gradually decreased. The distance of the tunnel expansion’s influence on tangential stress is about 0.91 to 1.45 times the tunnel span. The largest value of vertical displacement had a linear relationship with shaft depth, and the largest value of horizontal displacement had a quadratic relationship with shaft depth. Changes in the width–span ratio only had a greater impact on the ventilation shaft section. These results can provide a reference for similar in situ expansion projects.