Study On Shear Characteristics Of Interface Between Calcareous Sand And Concrete

With the gradual advancement of the South China Sea development strategy,the need of building wind farms,ports and docks,airports,lighthouses and even tourist attractions and urban facilities on the reefs of the South China Sea is also increasing.However,the pile foundation in calcareous sand is not only faced with complex loads such as wind,waves,and currents,but also restricted by the nature of the calcareous sand,such as irregular particle shape and breakable.Therefore,it is particularly important to carry out research on the physical and mechanical properties of calcareous sand.In this paper,the contact characteristics of calcareous sand with different particle sizes was tested.In this laboratory test,the direct shear instrument was used to simulate the shear characteristics of the contact surface between the calcareous sand and the concrete.Subsequently,the PFC was used to establish a pile-soil contact model to discuss the macroscopic and mesoscopic behaviors at the surface of calcareous sand and concrete.In summary,the main conclusions of this study are as follows:(1)The direct shear test is carried out to analyze the contact behaviors on the surface between the calcareous sand and the concrete.The contact surface of concrete is full of with scratches.A concrete block is placed at the bottom of shear box in the direct shear tests.The test results show that the roughness of concrete has a significant impact on the shear strength.As the roughness increases,the peak shear strength increases,and the corresponding shear displacement decreased.(2)Compared with the direct shear test,the simple shear test has the characteristics of unfixed shear surface and free deformation of the soil sample,which can simulate the actual working conditions.Therefore,the single shear test was used.It shows that there is a good linear relationship between the shear strength of the contact surface and the normal stress.The shear strength of the contact surface can be described by the friction angleφ_m of the Mohr-Coulomb strength criterion.The results show that the roughness of the contact surface and the relative density of coral sand have a certain influence on the friction angle.In the case of the same roughness,the friction angle increased with the increase of compactness or roughness.(3)Different from the continuous numerical analysis theory,the PFC discrete element is a discontinuous medium analysis method.In this chapter,the pile-soil contact model is established in the PFC analysis software,and the numerical simulation of the contact surface between calcareous sand and concrete is carried out.In the program,the number of broken bonds is used to intuitively describe the breakage of particles.The results show that with the increase of normal stress or shear displacement,the number of broken bonds increases significantly,and the shear strength of the shear plane decreases.This shows that the degree of particle breakage has a good negative correlation with the shear strength.(4)The shear results of the contact surface between calcareous sand and concrete show that,in addition to the effects of normal stress,contact surface roughness and particle breakage,the particle shape also has a significant effect on the shear characteristics of the contact surface between calcareous sand and concrete.For the near-spherical particles,the relationship between shear displacement and shear stress shows a slow growth.For the rhomboid particle cluster,the relationship between shear displacement and shear stress showed a steep decline,and the stress dropped sharply when the peak shear stress reached 130 kPa.