Experimental Study On The Stability Of The Excavation Conditions Of The Surrounding Soil Of A Steel Pipe Pile With Lateral Support

With the rapid development of urban construction in China,the development and utilization of underground space is attracting more and more attention.In particular,with the increase of the number of cars,the defects of the existing buildings,such as the lack of underground parking facilities,are becoming more and more obvious,and the underground space of the existing buildings needs to be developed urgently.Under the existing building,a new basement is built.We need to borrow the pile foundation of the original building,or add new pile foundation to bear the upper load,and then dig the earth.During excavation,with the decrease of the surrounding soil,pile foundation is gradually exposed,which not only affects the lateral friction of piles,but also causes the buckling stability of piles to decrease obviously.Steel pipe pile is a common form of pile base underpinning.In order to improve the buckling stability of steel pipe pile,the lateral support on the steel pipe pile can be set up in order to improve the buckling stability of the steel pipe pile,which can reduce the pile length and improve the buckling stability of the steel pipe pile.In this paper,the stability of piles under lateral excavation is studied.(1)the influence of different support position,support stiffness,support form and different excavation ratio on buckling stability of steel pipe pile is studied,and the design method of steel pipe pile with lateral support is proposed.(2)the ratio relationship between the axial force and the axial force of the pile is studied,which provides a basis for the design of support.The results show that:(1)under the condition of 0.667 constant excavation ratio,when the lateral support is located at the length of 45% piles at the top of the pile,the maximum buckling load of the steel pipe reaches the maximum value(522kN),which is the best position to support.The buckling load is increased by 21% compared with the same excavation than those without support.(2)when a support is set up and the position is located in the middle of the pile body(long range of pile top 37%~53% pile)and the two support is set up,the buckling failure of the steel pipe pile is a holistic instability.In other cases,the buckling limit load of the single leg instability(3)of the steel pipe pile increases with the stiffness ratio of the support to the steel pipe line.When the line stiffness ratio is more than 3.5,the trend of increase gradually slows down.(4)the ultimate load of steel pipe with scissors support is larger than that of horizontal support,and the limit load of two supporting steel pipes is larger than that of one support.Based on the test results,a design method of three forms of steel pipe piles with a horizontal support,two horizontal support and a scissors support is proposed.The calculation results are compared with the test results to calculate the error of 9.1%(one horizontal support)and 3.5%(two horizontal support).Sex.According to the relationship between the line stiffness ratio and the buckling ultimate bearing capacity of the pile,the support line stiffness ratio should be controlled at about 3.5.When setting horizontal support,the ratio of support axial force to axial force of steel tube is 0.4.When setting scissors support,the ratio of support axial force to axial force of steel tube is 0.6.