Design And Construction Of A Deep Foundation Pit In Zhengzhou

Since the 21st century,with the acceleration of China's modernization process,urban construction is developing rapidly towards the direction of large underground space.The appearance of super deep and super large foundation pit makes people have more strict requirements on the stability of foundation pit envelope,and the relevant normative documents become more and more mature and perfect.Main contents of this paper:(1)The deep foundation pit is an irregular quadrangle with a maximum side length of 232m in the east and west direction and 153m in the south and north direction.The foundation pit covers an area of about 25025 m2,and the maximum depth of foundation pit excavation is 22.95m.The soil layer is mainly silty soil,silty clay and fine sand.The upper soil-nailing wall and the lower pile+steel support+bolt are used in the support scheme.(2)In the 3-3 section with complex overload and the deepest depth,lizhengshen deep foundation pit software was used to analyze the foundation pit support.The section was divided into two parts in the design,namely the soil nail wall part and the pile row part.The analysis shows that three rows of soil nails are set on the upper soil nail wall,and the length of soil nails is 6m.There are 6 steel supports at the bottom,with a vertical spacing of 2.5m and 1 anchor cable at 1.45m away from the bottom of the foundation pit.The length of supporting pile reaches 52.95m,the embedding depth of supporting pile is 35m and the length of anchor cable is 36m,satisfying the checking calculation of overall stability.(3)In order to effectively control the displacement of the foundation pit and prevent the deformation of the ground wall,basin-type excavation is adopted in the middle of the foundation pit,and the principles of stratification,partitioning,symmetry,balance and time limit are followed.Within the range of 8m?10m from the excavation side line,earthwork excavation shall be cut off and crossed with support stratification.Bored pile is used as slope protection pile.Bored pile and high pressure rotary jet grouting pile form water curtain.(4)There are many problems in the construction.The soil nailing wall on one side cracked due to the steep slope and the action of water.In order to reduce the cracking of the pit wall,treatment measures should be taken quickly to pile up the earthwork along the pit wall.Backfill of earthwork is the fastest and most effective treatment method to prevent the cracking of the pit wall.Secondly,the lateral enclosure is moved outwards,and the slope is modified manually to reduce the slope to maintain the soil stability.Finally,to improve the soil stability,a micro pile is driven along the side foundation pit at an appropriate distance from the slope top.(5)66 horizontal and vertical displacement monitoring points were set up at the top of slope and crown beam,with an interval of 20m,to monitor the horizontal and vertical displacement around the foundation pit.In order to monitor the settlement of surrounding buildings,21 settlement monitoring points are set around the high-rise buildings in the south.There are 14 deep horizontal displacement monitoring points spaced 50m apart to monitor pile inclination.There are 54 stress monitoring points of pile body to monitor the stress of reinforcement.Figure[50]table[36]reference[40]...