Stability Analysis Of Sparse Piles For Pile-Supported Roadbed In Soft Soil Foundation Piles

In recent years,China highway project business continues to develop,which has brought many influences to China’s economic and social development.On the one hand,the highway network is gradually improving and the mileage is increasing,which injects new and powerful impetus into China’s economy;On the other hand,in the soft soil watershed of the floodplain of the Yangtze River,due to poor soil properties,improper design and construction,or overweight stacking,the problem of sparse pile stability of highway abutment columns is not uncommon,causing serious damage to economic and social development.The stability analysis of this problem is very important.The main content of the stability of sparse piles in soft soil foundation piles is the passive pile problem caused by the large displacement of the surrounding soil on the piles.At present,domestic and foreign scholars have carried out a lot of research on this,and proposed theoretical analysis methods such as elastic analysis method,cantilever pile method,and matrix transfer method.The solutions to the pile-soil flow,active lateral soil resistance and passive lateral soil pressure are given.In addition,the effect of multi-row piles has been studied,and rich results have been obtained.However,for some cases,especially the pile-soil interaction relationship and the definition of the passive segment are simplified;the solution of the differential control equation is not considered enough,and the above problems affect the accuracy of the results.Based on the basic assumptions of material mechanics,this paper establishes the differential control equation of the passive pile,and then gives the power series degradation solution and the error-free closed analytical solution considering various influencing factors.Then,the load thinning effect of the hard shell layer,the range of the passive segment and the p～y curve are studied.Finally,based on the matrix transfer method,the displacement internal force stability analysis theory of passive piles is solved in sections.Combining the Qili River Bridge Project in Nanjing Jiangbei New Area and the Qinhuai River Channel Renovation Project,a matlab program was compiled to perform calculation analysis and verification on the two projects.The main research work of this paper is as follows:（1）Considering the force characteristics of different sections of the passive pile respectively,the solutions of the degraded internal force and displacement of the passive pile under different working conditions are given.The solutions that can be considered in this solution include pile side friction,p～Δeffect,distribution function of soil resistance,and load distribution form in passive area.For the ideal situation where the pile side friction resistance and the self-weight of the pile are not considered and the"K₀"method is used to consider the effect of soil resistance.A closed analytical solution of differential equations is established based on differential equation theory.Considering the characteristics of the pile cap section and the free section,the corresponding displacement internal force transfer matrix is established（2）The load diffusion effect of the hard shell layer is studied based on the solution of the passive pile differential governing equation,the range and size distribution of the hard shell layer for the upper load diffusion is given.According to the undrained shear strength of soft soil and the form of stress distribution in soft soil foundation,a method for solving the distribution range of passive section is given.Based on the Sullvin model,considering the stability requirements of the soft soil foundation pile bearing roadbed,the simplified p～y curves of different soil types,such as soft,medium and hard,were deduced by linear fitting method.（3）Based on the solution of the passive pile differential equation for the soft soil foundation.Considering the boundary conditions when the top of the pile is free or embedded,and when the end of the pile is free or embedded,combined with the analysis of the load diffusion effect of the hard shell in the passive pile,the scope of the passive section methods,the simplified p～y curve and the effect of multi-row pile caps are used to establish the passive pile dredging stability analysis theory of the pile-supported roadbed in the soft soil foundation.（4）Combined with engineering examples,the feasibility and reliability of the theory established in this paper are verified,and the main reasons for engineering accidents are analyzed.Then it gives some suggestions during construction in the project where passive piles are likely to be generated in soft soil foundation pile-supported roadbed and the experience and practice of follow-up treatment of engineering accidents,in order to provide experience for related projects.