Character Analysis And Application Of Support Structures For Deep And Large Foundation Pit

The development of urban construction has led to an increasing demand for underground space,and the number of deep and large foundation pit projects has also increased.The foundation pit support structure is various in form and has strong regional characteristics.For deep and large foundation pits,the supporting structure form mainly adopts pile combined support or wall combined support.The annular inner support has been widely used in recent years,but there are also some problems.Based on the summary of the application and research status at home and abroad,this paper studies the support structure of row piles or underground continuous walls with internal support.The research contents include the stress and deformation behavior of the inner support structure under different arrangements of the inner support plane of the ring,the force and deformation of the support pile(wall)under different arrangement modes of the support vertical,and the stress and deformation behavior of piles(walls)at different insertion ratio of the support pile(wall).Finally,combined with engineering examples for comparative analysis,the following conclusions were obtained through research:(1)The analysis of flat layout of circular inner support: the statically indeterminate structure with redundant constraints is adopted for circular inner support;and overall structure with coupling beam arranged by radiation support can positively improve the overall deformation condition of the structure;the bigger the diameter of ring beam,the smaller the stiffness is and consequently the more severe the deformation will be.The bigger the spacing between support rods,the more severe the structure deformation will be;the bigger the stiffness of the support rod is,the smaller the structural deformation will be;the larger the section size of the support rod is,the smaller the structural deformation is.However,for the inner support structure subjected to a constant load,the increasing section size of rod makes little influence to the structural force bearing and deformation condition.Multiple concentric beams play a positive role in reducing the overall deformation of the inner support structure,avoiding or reducing the antisymmetric loads occurs to the inner support structure.(2)The analysis of the vertical arrangement of inner support: when using one layer of inner support,the height of the support should be 0.4 times of the excavation depth of the foundation pit;when adopt to the inner support of the two layers and the height of the support in the first layer is 2.0 m,the height of the support of the second layer should be taken.0.6 times excavation depth of foundation pit.(3)The analysis of the insertion ratio of the support pile(wall): increasing the insertion ratio,the maximum horizontal displacement of the retaining pile is gradually reduced,but after the insertion ratio exceeds 0.7,the increase of the insertion ratio has less influence on the horizontal displacement and bending moment of the supporting pile(wall).(4)Taking a deep and large foundation pit engineering example as the background,the analysis of the supporting structure of the underground continuous wall combined with the two-layer circular inner support is carried out,and the rationality of the finite element model is verified by the measured data.It is concluded that the maximum settlement of the ground caused by excavation of the foundation pit is mainly located near the excavation depth of the foundation pit.