Experimental Study On Particle Breakage Of Carbonate Sand Considering The Influence Of Loading Rate And Stress Path

Carbonate sand is a granular material rich in calcium carbonate,distributed in the sea area between 30°north and south latitude,such as the South China Sea.Carbonate sand is mainly produced by various reactions of marine organisms such as coral.Carbonate sand has the characteristics of irregular particle shape,more pores in the particle,and lower particle strength.Scholars at home and abroad have carried out comprehensive research on carbonate sand,a special geotechnical material.The conclusions point out that particle breakage plays an important role in the physical and mechanical properties of carbonate sand.In this paper,the carbonate sand obtained from the South China Sea is selected as the research object to study the effects of loading rate and stress path on the physical and mechanical properties and particle breaking properties of carbonate sand.The specific content can be summarized as follows:（1）The Hopkinson pressure bar tests and one-dimensional compression tests were carried out using a carbonate sand sample with a single particle size（focused on 0.8 mm～1.25 mm）,and two representative strain rates(1000 s^-1 and 0.001 s^-1)was selected for dynamic loading and quasi-static loading tests under different terminate stresses.The particle size distribution of the sand samples before and after the tests was measured using a laser particle size analyzer,and the amount of particle breakage was analyzed and the relationship between the terminate stress and the specific work was studied.The results show that the strain rate has a certain effect on the stress-strain curve of carbonate sand samples,but it is not very significant.The stress–strain curve under dynamic loading exhibits solid-like curve characteristics.Under dynamic loading conditions(1000 s^-1),different terminate stresses will cause different particle breakage modes in the sand sample,resulting in a platform phenomenon in the particle size distribution curve.In addition,the relative breakage extent and breakage efficiency under quasi-static loading(0.001 s^-1)are higher than those under dynamic loading(1000s^-1).Regardless of the dynamic loading or quasi-static loading conditions,the relationship between the relative particle breakage extent and the specific work is consistent with the energy dissipation theory.（2）The true triaxial tests were carried out using a carbonate sand sample with a single particle size（focused on 0.6 mm～1.0 mm）.Option 1:Four stress ratio values（0.3,0.6,0.9,and 1.2）were selected as the end point of the test,and the stress paths require the mean effective stress of 1 MPa and the intermediate principal stress parameter of 0,0.35,0.65,and 1.0.Option 2:Four mean effective stress values（200,400,600,and 800 k Pa）and four intermediate principal stress parameter values（0,0.35,0.65,and 1.0）were selected for 16 sets of tests.The results show that the stress–strain curves and volume–strain curves of carbonate sand samples are similar to those of quartz sand samples at lower stress levels.The shear stress decreases with increasing b value and increases with increasing p value.The peak friction angle is between 45.2°and 64°,and the maximum dilation angle is between 5.32°and 25.05°.However,at higher stress levels,due to particle breakage,the dilatancy characteristics of dense carbonate sand samples are suppressed.In the true triaxial test,the relative particle breakage index of carbonate sand increases with the increase of p value,and it decreases first and then increases with the increase of b value.Moreover,there is a hyperbolic function relationship between the relative particle breakage index and the input energy for carbonate sand,which also satisfies the energy dissipation theory.