Study On Shear Mechanical Properties Of Pile And Sand Interface

Pile foundation is widely used in various buildings and structures,which has the advantages of high bearing capacity,strong stability and high degree of mechanized construction.The pile-side friction is the main component of the pile bearing capacity,and its accurate calculation is conducive to clarifying the pile bearing capacity,so as to provide the basis for improving and optimizing the pile foundation design.At the same time,the problem of pile-side friction is essentially the problem of interface shear characteristics between soil and structure,and the existing research mostly uses the interface shear equipment between soil and structure to simplify the analysis.However,there are some problems in the process of interface shear,such as the uncertainty of normal stress state,the uncertainty of contact surface area and the lack of axial symmetry.The accurate description of the interface shear characteristics between pile and soil is the basis for improving the accuracy of pile-side friction calculation.In this paper,a series of experimental studies on the shear characteristics of the interface between sand and pile are carried out.The mechanical properties of sand are analyzed by laboratory tests,and the relative density calibration of sand is studied by sand rain method.The interface shear test between sand and pile is carried out by using a new type of interface shear device.On this basis,the calculation model of the interface shear force between sand and pile is established.Specific research contents and results are as follows:(1)Through screening test and conventional triaxial consolidation drainage shear test,the particle size composition and strength of soil are determined.Based on the sand-rain method,the calibration test of the relative density of sand was carried out,and the influence of falling distance,mesh aperture and mesh spacing on the relative density of sand was analyzed.It was obtained that the relative density of sand increased nonlinearly with the increase of falling distance,decreased with the increase of mesh aperture,and increased with the increase of mesh spacing.At the same time,combined with the calibration results of the relative density of sand,the relationship between the relative density of sand and the spacing,mesh aperture and hole spacing was quantified.(2)The interface shear characteristics of sand and pile under different normal stresse s,different relative densities,different materials,different surface roughness and different pa rticle gradations were studied by using a new type of interface shear equipment(axisymmetr ic).The test results show that the decrease of the relative density and average particle size of the sand sample will lead to the decrease of the boundary shear strength,and the larger the r elative density of the sand sample is,the more obvious the dilatancy phenomenon is.The lar ger the surface roughness of the pile is,the larger the peak shear strength and the correspondi ng displacement are,and the more obvious the strain softening phenomenon is.Increasing th e surface roughness of the pile side within a certain range can effectively improve the shear s trength at the contact surface,thereby improving the ultimate bearing capacity of the pile fou ndation.With the increase of normal stress,the peak shear stress and corresponding displace ment also increase,and the normal displacement of sand particles at the contact surface show s a decreasing trend.The larger the normal stress is,the faster the dilatancy rate is.(3)Based on the above shear test results of pile-soil interface,the empirical equation of-relationship curve considering the influence of normal stress is established.In the expression,the parameter a is linearly correlated with_,and the parameters b and c are power functions with_.Compared with the previous models(hyperbolic model,Prevost model and Hu Qijun model),it is found that the model established in this paper is more consistent with the test data,which has certain reference and applicability for the study of mechanical properties of pile-soil interface.