Behavior Analysis And Optimization Design Of Prefabricated Support Structure For Foundation Pit Of Underground Intelligent Garage

With the increasing number of urban cars and the emergence of parking difficulties,underground intelligent garage came into being.The underground intelligent garage covers a small area and has large storage capacity.It is often built in the urban center with dense buildings.Therefore,it mostly adopts the fabricated support structure.After the construction is completed,the Larsen steel sheet pile used as the support structure can be recycled.Based on the three-dimensional,standardized and mechanized characteristics of underground intelligent garage,most of its foundation pit works are foundation pits with regular shape,small excavation area and two or more excavation depths,namely asymmetric excavation foundation pit.For the asymmetric excavation of foundation pit,different excavation depths make the stress distribution of the support structure on both sides of the foundation pit asymmetric,resulting in asymmetric deformation,and even the overall translational displacement to one side,resulting in the "push back" displacement of the support structure on the shallower side of the excavation,and the stress deformation of the foundation pit is more complex.Therefore,it is of great theoretical significance and engineering value to study the stress and deformation law of foundation pit fabricated support structure under asymmetric excavation.According to the characteristics of the foundation pit engineering of underground intelligent garage,this paper establishes the calculation model of the foundation pit with asymmetric fabricated support structure under the condition of asymmetric excavation by using the finite element software ABAQUS,analyzes the stress and deformation law of the support structure in the process of foundation pit excavation,further studies the influence of the support structure parameters on the stress and deformation of the foundation pit,and finally optimizes the original support scheme combined with the engineering case.The main work is as follows:(1)Based on the actual engineering case,the finite element model of the prefabricated support structure of the foundation pit under the condition of asymmetric excavation is established by using the finite element software ABAQUS,and the laws of the vertical deformation of the foundation pit soil and the stress deformation of the support structure are analyzed.It is found that under the condition of asymmetric excavation,the deformation of the soil on the deeper side of the excavation is greater than that on the shallower side of the excavation,and the lateral deformation curve of the support piles on both sides is asymmetrically distributed,The whole supporting structure moves horizontally to the shallow side of excavation;When multi-channel internal support is adopted,asymmetric excavation has the greatest influence on the change of axial force of the support in the lowest channel;Under the condition of asymmetric excavation,the asymmetric support structure of foundation pit will reduce the asymmetric deformation difference of soil on both sides.(2)Based on the single factor analysis method,the stress and deformation law of the support structure of asymmetric excavation foundation pit is analyzed when the internal support stiffness,the internal support spacing and the embedded depth of the support pile are different.The research shows that with the decrease of the internal support stiffness,the deformation of the supporting piles on both sides to the pit increases,the deformation of the shallow side supporting piles is more obvious than that of the deep side supporting piles,and the displacement of the shallow side supporting piles pushed back decreases;With the increase of the internal support spacing,the translational displacement of the whole support structure due to asymmetric excavation decreases,and the internal force of the shallow side support pile is larger than that of the deep side support pile;Reducing the embedded depth of the shallow side support pile can make the soil deformation on both sides of the foundation pit more consistent,and has little impact on the internal force change of the support pile on both sides.Therefore,for the asymmetric excavation of the foundation pit,the pile length of the shallow side support pile should be reasonably selected.(3)Considering the influence of asymmetric excavation on the stress and deformation of internal support structure,according to the elastic integral structure method and the principle of minimum potential energy,the lateral deformation curve equation of support structure is established,the lateral deformation curve coefficient of support structure is calculated by MATLAB software,and the theoretical calculation value is compared with the numerical simulation result.(4)Combined with practical engineering cases,the stability analysis method is used to explore the influence of internal support stiffness,internal support spacing and embedded depth of support pile on each key evaluation index of foundation pit,so as to optimize the support scheme.The results show that for asymmetric excavation foundation pit,the change of internal support stiffness has the least influence on the key indexes of shallow excavation foundation pit,and the change of shallow support pile embedded depth has the least influence on the key indexes of deep excavation foundation pit;Based on the above analysis,the internal support stiffness and shallow side support pile length are optimized.The optimized scheme not only meets the stability and safety requirements in the process of foundation pit excavation,but also reduces the asymmetry of foundation pit deformation,reduces the engineering cost,and achieves an ideal optimization effect.