Experimental Study On Single Pile Bearing Capacity Of PHS-Cement Soil Composite Pile

As a new type of pile composed of multiple single pile types,composite piles can make use of the advantages of different pile types to complement each other.It has the characteristics of convenient construction,low cost,and reduced environmental pollution,and has broad development prospects.At present,the domestic research on the bearing characteristics of composite piles is mainly concentrated in areas with a large area of soft soil such as Shanghai,Tianjin,Nanjing,etc.The core of rigid composite piles is mainly composed of PHC piles,and there is little research on the application of PHS piles as the inner core.Based on the field test results of three PHS-cement-soil composite piles at the Furong Lake civil construction site in Zhoukou City,Henan Province,Research on the bearing characteristics of single PHS-cement-soil composite pile by study the friction characteristics of contact surfaces through indoor friction tests、theoretical analysis of the force state of composite piles and numerical simulation method using large general software ABAQUS,The main research contents are as follows:The interfacial characteristics of the two contact surfaces(cement-soil-soil interface,C80 concrete-cement-soil)of composite piles were analyzed through indoor friction experiments.The results show that there are not only elastic deformation but also plastic deformation at the cement-soil-soil interface,and the characteristic performance of brittle failure with the increase of ash content;The friction coefficient of the contact surface decreases with the increase of the normal pressure and then gradually remains stable,and the residual friction coefficient appears.The friction test results of the cement-soil-C80 concrete interface show that the friction coefficient of the cement-soil-concrete interface increases with the increase of the ash content,and decreases with the increase of the normal pressure,and the rate of decrease becomes smaller and smaller;With the incorporation of cement improved interface from plastic collapse into brittle failure;The relationship between the shear strength of the cementsoil-concrete interface and the normal stress conforms to Coulomb’s law.Using ABAQUS software to simulate the contact surface model analysis under different normal stresses,The friction coefficient obtained through the indoor experiment defines the friction coefficient of the model contact surface,and the feasibility of defining the model contact surface by the friction coefficient is obtained;Obtain the residual friction coefficient of the cement-soil-soil interface through laboratory tests,establish a composite pile model with friction coefficients of 0.1,0.4,0.8,and simulate the settlement displacement of the composite pile under different friction coefficients of the pile-soil interface.The results show that the friction coefficient is between 0.1 and 0.4.It has a greater impact on the settlement of composite piles.Through ABAQUS finite element calculation results,the axial force distribution curve of equal core composite pile under vertical load is obtained and the load sharing ratio of pile tip and pile side is 15%and 85%respectively,so the composite pile behaves as friction pile;Compare the transfer process analysis of composite piles,PHS piles and cement-soil piles under the same load,the displacement and deformation of cementsoil piles are mainly concentrated on the upper part,gets the downward load transfer capacity is weak,which is characterized by friction piles;The difference in settlement between PHS pile and composite pile is small,and the layer-by-layer load transfer is the manifestation of the composite pile under the macroscopic stress state.