Crushing Behavior Of Quartz Sand-gravel Particles And Its Fractal Features Under Confined Compression

Particles crushing of quartz sand-gravel means that the constitutes are broken or damaged into smaller particles under the exterior loads.Particles crushing will arose the change of structure and then affect the physical quality.A confined compression test and a direct shear test were used to investigate the crushing behavior of quartz coarse sand and fine gravel particles under different compressive stress,and measure the breakage by B₁₅,B_6o,B_g andB_r.The relative breakage ratio B_r could measure the integer breakage effectively.The test results show that particles break up when the pressure come to a certain level,and break-point stress of fine gravel particles is about 12.8MPa;break-point stress of coarse sand is about 25.6MPa.The relationship between Hardin index and compressive stress can be expressed by semilogarithmic linear curves.The correlation coefficient R=0.9732～0.9909.The particle breakage value increase with the increasing of compressive stress and related to particle size.In the same case, larger partical size and bad match with higher breakage ratio.The hardness of particle also contribute to the breakage index.With the increasing of particle breakage value, the angles of fraction increase for coarse sand,and increase at first and then decrease for fine gravel.Both have the tendency finally to value unvaried when particle breakage value is large enough.The fractal crushing is studied based on fractal concept and the measured data of particle-size distribution.Analysis by the linear fitting indicated that the fractal crushing dimension D fluctuated between 0.482 and 2.539.The fractal research shows that the particle-size distribution after particle breakage exhibits a statistical fractal feature.The correlation coefficient R=0.9137～0.9957.The magnitude of fractal crushing dimension reflects the particle-size,distribution and the variation of particle breakage value.Large fractal crushing dimension corresponds to large particle breakage value.There exists close relationship between fractal crushing dimension and Hardin's particle breakage index. The relationship between fractal crushing dimension and compressive stress can be expressed by hyperbolic curves.As a result,fractal crushing dimension and Hardin index can be evaluated as long as compressive stress and parameters of soil particles are obtained.The fractal crushing dimension may be useful indicator for quantitative analyzing the particle breakage of granular materials.The results of study represent a optimistic foreground in a certain extent.The fractal crushing dimension may be a new index for the estimate of particle breakage.