Research On Microstructure Characterization And Particle Breaking Behavior Of Carbonate Sand

In recent years,with the rapid development of island and reef construction,carbonate sand,a special geotechnical engineering medium,has attracted more and more attention from experts and scholars.Different from traditional quartz sand,carbonate sand particles have a complicated shape and well-developed internal pores,which result in different engineering characteristics between carbonate sand and quartz sand.In order to obtain a deeper understanding of the physical and mechanical properties of carbonate sand,threedimensional images of carbonate sand particles are obtained with the help of high-precision CT scanning and the corresponding image processing technology.The morphology and pore structure of carbonate sand particles are characterized.Furthermore,the relationship between the micro structure of carbonate sand particles and their crushing behavior is discussed through the single particle crushing test and its simulation,which provides a theoretical basis for clarifying the essence of the crushing behavior.Firstly,the carbonate sand particles which size are 3-5mm are randomly selected,and by using CT scanning,the three-dimensional images of these carbonate sand are obtained.Simultaneously,using image processing technology,three-dimensional binary images of individual carbonate sand particle and their internal pores are obtained.Among them,the threshold segmentation is used to obtain the three-dimensional binary image and the surface of carbonate sand particles is smoothed by the Closing algorithm to make the identification of a single particle more accurate.After identifying individual carbonate sand particles,this thesis uses morphological parameters such as sphericity,aspect ratio,and pore size distribution to characterize the morphology and internal pores of each particle.At the same time,the permeability coefficient of the internal pores is calculated.The result shows that,unlike ordinary quartz sand,carbonate sand particles have a more complex structure,lower sphericity and convexity than quartz sand particles.The absolute permeability of the internal pores is related to its own internal porosity and Euler characteristic.Secondly,with the aid of in-situ CT scanning of single particle crushing test of carbonate sand,the crack growth and fragment morphology evolution in the is studied.After analysis,it is found that the cracks tend to expand along the larger defects inside the particle,and the broken fragments tend to be more bladed than the original particles.Finally,based on the CT data of carbonate sand particles,a coupled discrete-continuous analysis(FDEM)model is established to accurately simulate the crushing process,and the influence of pore structure in carbonate sand particles on its crushing behavior is explored.The results show that the porosity and the pore structure of carbonate sand particles will directly affect the crushing strength and crack distribution.