Research On Optimal Design Of Deep Foundation Pit Support For An Underground Intelligent Garage In Xi’an

At present,there is no unified theoretical method and technical specification for the design calculation of the pile and brace composite support form of ultra-deep foundation pits.The design of the support structure refers to the traditional deep foundation pit design method,and the design results are often conservative,resulting in support Cost is higher.Therefore,there is a need to further optimize the support design,which can save the support cost and reduce the project cost.The thesis relies on the deep foundation pit project in the underground garage key technology research and development and engineering demonstration project,with the goal of reducing the support cost,for the cast-in-situ pile + horizontal internal support support system,through theoretical analysis and numerical calculation And other research methods to study the effect of factors such as pile diameter,pile center distance,embedding depth and horizontal support stiffness on the foundation pit support system and surrounding soil body,as well as the law of stress and deformation,while being sensitive to the degree of influence of each parameter Analysis,and on this basis,the optimization parameters were determined.The main conclusions of the paper are as follows:(1)With the decrease of the equivalent wall thickness,the maximum vertical surface displacement increases faster after the wall thickness is less than 0.73 m,but the maximum shear force and bending moment of the wall structure show a decreasing trend;The vertical displacement of the surface and the horizontal displacement of the envelope structure are weakly affected by the embedding depth,but the shear force and bending moment of the envelope structure decrease rapidly after the embedding depth is less than 7m;When the horizontal support stiffness decreases,the maximum vertical displacement of the ground surface and the maximum horizontal displacement of the pile increase greatly.The positive and negative shear forces of the pile have opposite development trends,and the bending moment shows an increasing trend.(2)Knowing from the size of the sensitivity coefficient,the effect of the horizontal support stiffness on the vertical displacement of the ground surface and the horizontal displacement of the envelope structure is 4 times that of the wall thickness and 80 times that of the embedded depth.For the shear and bending moment of the envelope,the equivalent wall thickness is the most significant influencing factor.(3)After optimization,the embedding depth of the pile in the supporting structure is reduced to 9m;the pile diameter is reduced by 200mm;the pile center distance is unchanged;the horizontal support stiffness remains unchanged from the original design value.After calculation,the comprehensive optimization of the foundation pit support project can save 142,1992 yuan in engineering cost,which is 14.9% less than the total cost of the initial plan support,and achieves the purpose of cost saving.(4)The research results show that optimizing the supporting scheme for insensitive impact factors can effectively save construction costs and shorten the construction period.It is a feasible foundation pit optimization direction and has good application value.It can provide reference and reference for the optimization of the similar deep foundation pit engineering support system in the future.