Research Of Application Of Single Layer Large Section Reinforced Concrete Inner Bracing In Deep Foundation Engineering Pit In Soft Soil Area

The development and utilization of underground space has given rise to a large number of foundation pit projects.Deep foundation pit projects in soft soil areas in China are often in relatively complex urban environments.In general,internal support structures are used for the safety and stability of foundation pits.In deep foundation pits in soft soil areas,deep foundation pits are generally provided with multi-layer reinforced concrete internal braces.For example,at least 2 layers of reinforced concrete internal supports are used in foundation pits above 12.5m in Tianjin soft soil areas.The safety and stability of the project,but generally speaking,the stress level of the main bearing members of the reinforced concrete internal support is low,resulting in waste of material strength,high cost and long construction period.On the premise of ensuring the stability and safety of the foundation pit,if the number of horizontal supports in the deep foundation pit can be reduced,the construction cost can be effectively reduced and the construction period can be shortened.In this paper,a 14.9m deep foundation pit project in Tianjin soft soil area is taken as the research object.Through the comparison of design options,site monitoring,and finite element simulation,the use of higher-strength grade concrete,large-section single-layer internal support,and large-diameter support Deformation and internal force characteristics of the pile foundation pit support system,and the parameter research was carried out using finite element software.The following conclusions were obtained through systematic research:(1)Using Lizheng deep foundation pit software to calculate and analyze the two sets of design schemes with single-layer and double-layer internal support systems,and conduct a comparative study from the aspects of deformation and internal force.The calculation analysis shows that the single-layer internal support scheme is better than the double-layer internal support scheme.The material strength of the main stressing members is higher,which saves project cost and construction time.(2)Deformation data of the retaining pile wall and internal force data of the ring brace were obtained by conducting on-site monitoring of deep foundation pit engineering examples using large-section single-layer internal support and large-diameter supporting piles.The data were analyzed and summarized.The law of change of internal force.The research shows that the deformation law is consistent with the previous literature summary law,and it tends to the maximum value;the strength level of the concrete material of the main supporting members of the internal support which meets the requirements of the design code for the supporting structure of the foundation pit.(3)The ABAQUS finite element software was used to simulate the deep foundation pit,and the deformation of the retaining pile wall and the change of the internal force of the ring brace were compared.rationality.Based on the three-dimensional finite element model,the design parameters of the foundation pit are further studied,and the degree of influence of different design parameters on the deformation of the foundation pit is analyzed.The research shows that the factors such as the diameter of the supporting pile,the depth of the internal support position,and the strength grade of the concrete have a significant effect on the deformation of the foundation pit.