Load Transfer Mechanism Of Chemical Churning Pile-Mini Steel Pipe Pile Compound Foundation In Ningbo Soft Clay

The chemical churning pile-mini steel pipe pile compound foundation is a composite pile type suitable for foundation reinforcement in soft soil area.It is composed of mini steel pipe pile and chemical churning pile.In this paper,the force transmission mechanism of the combined pile foundation is studied through the combination of indoor model test,on-site prototype pile test and numerical simulation,in the following four loading modes respectively:overall compression,mini steel pipe pile compression,pull-out and horizontal loading.The main research of this paper is as follows:(1)Based on the indoor model test study,the stress distribution and failure mode of the model pile under different loading modes are obtained.(2)Through on-site prototype pile test,the soil physical parameters of the test site,the strength of the chemical churning pile and the pile top load versus displacement curve of the chemical churning pile-mini steel pipe pile compound foundation are obtained.(3)Based on the on-site prototype pile test,the numerical model of the combined pile foundation was established.The parameter settings of combined pile foundation interface,chemical churning pile and soil interface are analyzed.The constitutive model selection of the chemical churning pile material is discussed.And the accuracy of the numerical model is verified by the indoor and outdoor test results.(4)The force transmission mechanism of the chemical churning pile-mini steel pipe pile compound foundation in four different loading modes is numerically simulated respectively.The research shows that when the horizontal load is applied,the load criticality of the combined body is mainly controlled by the pile diameter of the chemical churning pile;when the mini steel pipe pile is vertically loaded,the load is mainly transmitted to the pile through the joint of the mini steel pipe pile and chemical churning pile interface,where the bonding force is mainly distributed at the upper end(the length is 10D_s)and the lower end(the length is 10D_s)of the mini steel pipe pile;when the combined pile foundation is under compression,the load is mainly transmitted to chemical churning pile through the bonding force at the bottom of the mini steel pipe pile;when the combined pile foundation is vertically loaded,the chemical churning pile,mini steel pipe pile and chemical churning pile interface,chemical churning pile and soil interface may be damaged near the top of the combined pile foundation and the bottom of the mini steel pipe pile.In addition,the effects of different sizes of mini steel pipe piles on the force transmission mechanism and bearing capacity of the combined pile foundation are discussed.(5)Through experimental research and numerical simulation analysis,the distribution assumptions of bonding force at mini steel pipe pile and chemical churning pile interface when the combined pile foundation is vertically loaded are analyzed reasonably.The calculation method of bearing capacity of combined pile foundation under vertical load is given.And the accuracy of the method is proved by the comparison between measured data.