Mechanical Properties of Deep Foundation Pit Support near High-Speed Railway Bridge in Coastal Soft Soil Stratum and the Environmental Impact

Objective When undertaking deep excavation construction within a river channel spanned by a high-speed railway bridge, the impact of river channel foundation pit construction on the adjacent high-speed railway bridge should be explored and its safety be evaluated. Therefore, it is necessary to carry out relevant researches. Method Based on a certain deep excavation project in soft soil river channel near high-speed railway bridge in Binhai District, Fujian Province, a research is carried out focusing on the load-bearing and deformation characteristics of SMW（soil mixing wall） method support structures. Taking into account the principle of support stiffness optimization, and requirements of structural and environmental deformation control, a foundation pit support scheme for the sensitive section near high-speed railway bridge is proposed and its rationality is verified through the trial section. Result ＆ Conclusion The slight disturbance of the soil with SMW pile construction method causes strata pressure, making the horizontal displacement of the support structure show a bow trend along the pile body, large in the middle and small at both ends. With the excavation of the foundation pit, the horizontal displacement curve of the support gradually transitions from the bow shape to a reverse bow shape along the pile body, the maximum displacement is transferred from the pile body to the pile top, and a "kicking" phenomenon occurs at the pile bottom. The support deformation tends to be stable after the U-shaped groove is constructed. Research shows that the range of 3.0H（H is the foundation pit depth） around the pit is the deformation influence area, the range of 1.7H around the pit is the key deformation influence area, and the settlement reaches the maximum value at 3 m around the pit. The settlement values of the wall and ground near the high-speed railway frame bridge are far less than the specified values, verifying the rationality of the calculation method and scheme.