Evaluation Of Physical And Mechanical Properties Of Calcareous Sand Based On Multi-functional CPT Testing

Calcareous sand is widely distributed in tropical and subtropical waters,including the South China Sea.It is an important building material for island and reef construction and marine engineering infrastructure construction in China.Therefore,under the strategy of maritime power and the Belt and Road,it is of great significance to study the physical and mechanical properties of calcareous sand in depth.In the existing literature,there is still a lack of research on the physical and mechanical properties of calcareous sand and the data interpretation of multi-functional CPT in-situ test parameters,so it is urgent to carry out relevant research.The main research contents and achievements of this paper are as follows:(1)The particle strength of calcareous sand is explored,the influence law of key influencing factors such as particle shape and coordination number on particle breakage of calcareous sand is clarified,and the micro mechanism is revealed.The effects of particle size,shape parameters and coordination number on the strength of calcareous sand were studied by single particle crushing test.The correlation model between particle characteristic strength and particle size of calcareous sand is established,and the distribution law of particle shape parameters is clarified based on statistical method.The discrete element numerical simulation is carried out to verify the test results,and reveal the micro mechanism of particle crushing strength and failure mode.(2)The effects of particle size,fine particle content and gradation on the physical and mechanical properties of calcareous sand are explored,and the correlation model of maximum and minimum void ratio,small strain stiffness and thermal conductivity of calcareous sand is established.Through the triaxial test,bending element test and thermal conductivity test,it is found that with the increase of particle size and fine particle content,the maximum and minimum void ratio and thermal conductivity first decrease and then increase,and the shear strength and small strain stiffness gradually decrease.With the increase of maximum particle size and the decrease of fractal dimension(non-uniformity coefficient),the small strain stiffness and thermal conductivity of calcareous sand will gradually decrease.(3)The multifunctional CPT penetration parameter analysis of calcareous sand is explored,and the multifunctional CPT in-situ parameter data interpretation model of calcareous sand is established.By calibrating the numerical simulation parameters and carrying out CPT penetration simulation,a model for predicting the relative compactness,internal friction angle and state parameters of calcareous sand based on CPT test parameters is established.Through the indoor multi-functional CPT penetration,the accuracy of predicting the physical and mechanical properties of calcareous sand based on multi-functional CPT is verified.In this paper,the effects of particle morphology,fine particle content,gradation and particle size on the physical and mechanical properties of calcareous sand are studied from the mesoscale and macro scale,and the theoretical models of particle strength,maximum and minimum void ratio,small strain stiffness and thermal conductivity of calcareous sand are established.Combined with numerical simulation and calibration tank test,a correlation model for predicting the physical and mechanical properties of calcareous sand based on multi-functional CPT is proposed,which is of great significance to the investigation of physical and mechanical properties of calcareous sand and the research of related mechanical properties.