Research On The Design And Monitoring Technology Of Deep Foundation Pit Enclosure Structure In Xi’an Metro

Design of the retaining structure and stability analysis of deep excavation in metro station is one of the key issues in metro construction.The study on the theory of deformation laws and monitoring of deep excavation in Xi’ an has great significance.In this paper,it uses the method that combines with the theoretical analysis,in-situ monitoring and numerical simulation followed the background of Deep Excavation in Weiqu South Station of Xi’ an Subway Line.The main jobs are as follows:(1)The deformation pattern of the deep foundation pit envelope structure and the influencing factors was analyzed and discussed.Among them,factors affecting the deformation of deep foundation pit retaining structures included engineering geology and hydrological conditions,pit geometry,design factors,construction factors,and external load changes.(2)The form of the deep foundation pit retaining structure in the section of Xinzhu-BaoShuiqu was determined,which was grading + cast-in-place pile + steel bracing.combined with the calculation method of row pile support and Rankine earth pressure calculation theory,the design of the deep foundation pit envelope structure was completed.At the same time,the feasibility of the design of the proposed deep foundation pit envelope structure was verified by FLAC numerical simulation method.The results showed that the design scheme of the envelope structure with grading + cast-in-place pile + steel bracing can ensure the deep pit during excavation.The safety and stability of the proposed design of the envelope structure is feasible.(3)Combined with engineering geology and hydrogeological conditions,the design of deep foundation pit dewatering in the newly excavated section of the newly constructed～bonded area was given.The results of water level monitoring showed that the design of precipitation is reasonable and the purpose of dry construction was achieved.(4)The design of deformation monitoring program for deep foundation pits was carried out and on-site monitoring was completed.The on-site monitoring results showed that the horizontal deformation of the retaining pile was too small to meet the allowable range,and the steel support can restrain the horizontal deformation of the pile during deep excavation of the deep foundation pit to some extent.(5)By comparing the numerical calculations and the on-site monitoring values,it could be sew that the deformation laws and deformation trends of the deep foundation pits were basically the same,indicating that the proposed design method for the deep foundation pit envelope structure was correct and correct.The horizontal displacement of the pile,the axial force of the steel support and the ground surface settlement were all within a reasonable range,indicating that the proposed sloping + cast-in-place pile + steel bracing envelope scheme was reasonable and effective.