Excavation Deformation And Stress Analysis Of The Ring Support System Of Deep Foundation Pit

With the rapid development of high-rise buildings,deep foundation pit engineering has become more and more important,and the safety of deep foundation pit construction has been focalized.In the construction of foundation pit,the deformation and stress of the supporting structure have a great influence on the safety of the foundation pit.Based on the foundation pit of the Caijia Xiang multiple-use building in Nanjing,this thesis makes a simulated analysis of the excavation deformation and stress of the annular support system in the deep foundation pit.The main contents are as follows:1.Several primary forms of foundation pit support are briefly summarized and the advantages and disadvantages of each are compared.The history,characteristics,application range and mechanical principles of the annular support system are introduced;the construction process and quality control keys of the ring support structure are also discussed.2.According to MIDAS/GTS finite element analysis software,this thesis makes a simulation of each construction stage in the process of excavation.Analysis has also been made of the variation law of the horizontal displacement of retaining structure in different depth and at different position of foundation pit edge,of the change rule of the ground surface settlement around foundation pit and the internal pit-bottom uplift,and of the distribution and variation in the supporting structure’s axial force.3.The four factors affecting the horizontal displacement of foundation pit retaining structure are analyzed,which includ the section size of the inner support,the around load of the foundation pit,the diameter of the retaining pile and the space between the retaining piles.Through the analysis,the following conclusions are drawn:1)Along with the excavation,the horizontal displacement of the enclosure structure is increasing,the displacement curve is parabolic,and the displacement mainly occurs in the middle and lower part of the excavation face.2)the horizontal displacement of the retaining structure at different positions at the edge of the foundation pit is different,the displacement in the middle of the edge is thelargest and the displacement near the edge corner is the least.3)the ground surface settlement around the foundation pit increases with the excavation,and the settlement curve is grooved.Heave amplitude increases with the excavation,and the uplift curve is arched.4)The axial force of the ring support is mainly under compression,showing four peak axial forces which are located in the direction of the four corners of the foundation pit,and it is the weak part of the supporting structure.5)the greater the surrounding load of the foundation pit is,the greater the horizontal displacement of the enclosure structure will be;the larger the cross section size of the inner supporting beam is,the smaller the horizontal displacement of the enclosure structure gets,while the trend becoms gradually slow;the larger the diameter of the supporting pile is,the smaller the horizontal displacement of the retaining structure grows,but the declining trend is gradually slow;the larger the space of the pile is,the greater the horizontal displacement of the retaining structure becomes.Through the simulation analysis of the deformation and stress of the foundation pit supporting system,this thesis provides some worthy reference for the design and construction of similar projects in the future,and has certain practical significance.