Study on deformation law of lattice columns in deep foundation pits in soft soil area

In soft soil area, the uplift of foundation pit bottom drives the lattice column to deform upward, which generates additional bending moment for concrete support. However, the secondary stress caused by the vertical deformation of lattice column is often not considered in the design of foundation pit at present, and there are few studies on this kind of problem, lacking the understanding of the deformation mechanism of lattice column and its influence. To clarify the deformation mechanism of lattice column is helpful to improve the understanding of the deformation of foundation pit in spatial supporting system, and to provide a theoretical basis for the deformation control of lattice column in design and construction. Combined with the monitoring data of deep foundation pit of open tunnel in Wenyi West Road, Hangzhou, and by changing model variables such as soil layer distribution, pit bottom reinforcement range, supporting structure depth, column pile depth and pile diameter, the influence mechanism and law of field monitoring and model variables on lattice column deformation were analyzed. The results show that: 1) The distribution of soil layer has a significant influence on the lattice column. The weaker the soil layer of foundation pit bottom is, the greater the influence on the lattice column deformation is. 2) The deformation of lattice column can be effectively reduced by increasing the depth and diameter of column. 3) Pit bottom reinforcement can reduce the deformation of lattice column, but there is a critical depth of reinforcement. 4) The depth of ground wall has a certain constraint effect on the upward uplift of lattice column, but the effect is not obvious.