Theoretical And Experimental Research On Unstable Bearing Capacity Of Miniature Steel Pipe Piles

Due to the advantages of low reinforcement cost and flexible layout,miniature steel pipe piles have been widely used in engineering such as retaining structures,slope support,transmission lines,etc.,and its lateral bending resistance has a lot of rese arch.However,it has only begun to emerge as a foundation for underpinning piles for building enhancement and reinforcement and rectification and correction in recent years,and it has been widely used in housing rectification.The vertical bearing capacity of the miniature steel pipe pile is calculated according to the empirical formula given in the basic specification,and the actual bearing capacity has less theoretical and experimental results.However,due to the small diameter,strong penetrati on,and the large slenderness ratio of the pile,the stability of the micro-steel pipe pile is not good.The instability and failure mode is the key to affecting its bearing capacity.Therefore,it is necessary to study the buckling stability of the miniat ure steel pipe pile,which has important guiding significance for practical engineering.There have been a lot of studies on pile foundation instability,but the traditional method of studying pile foundation instability has certain limitations,because th e deflection curve used is a hypothetical form,and the unstable load is an approximate solution.For piles with large slenderness ratio and low flexural rigidity,the theoretical calculation value and the actual value of the project are far from each othe r.Accurately solving the unstable bearing capacity has become an unavoidable problem for the popularization and use of miniature steel pipe piles,while solving the real unstable bending curve has become the solution the key to the problem.In this paper,under two basic assumptions,the pile-soil system is converted into a reasonable mathematical and physical model.The analytical formula of the instability and deflection curve of the miniature steel pipe pile is systematically solved,and the corresponding instability load is solved.The main work and main conclusions of this article are as follows:(1)Under the framework of Winkler elastic foundation beam,the deflection curve equations of pile foundation under vertical load are obtained by k,m,and c methods respectively,and the control equations of unstable load and related physical parameters are given.And use MATLAB to solve the corresponding unstable load(2)Under the condition of infinite pile length,when the foundation coefficient is assumed by the k method,the analytical expression of the unstable load is given.When the foundation coefficient is m and the c method is assumed,the analytical expression of the unstable load is fitted through the dimensional analysis method.(3)An indoor test was designed to verify the theoretical solution of the unstable load under different boundary conditions,different slenderness ratios,and different stiffness ratios;the correctness of the unstable theory was verified by actual engineering data.(4)The data of the actual unstable bearing capacity of the project was collected,and the difference between the theoretical value and the actual was compared and analyzed,which further verified the correctness of the theory.