Study On Evolutionary Regularity Of Particle Breakage Of Coarse-grained Soil

It is an important engineering problem to study the evolution regularity of the particle breakage of the coarse grained soil fillings under the impact load and to make a more accurate prediction at present.The quantitative description method,the influence factors,the evolution regularity of particle breakage and the application of the grey prediction model were firstly summarized in this study.Then the growth path method was established to deduce the ultimately two-dimensional fractal model and the ultimate fractal dimension of particle breakage of the coarse-grained soil.Thirdly,based on the compaction test,the breakage characteristics of coarse sand with angle and spherical glass beads were studied under the impact load and the unidirectional compression condition.Finally,on the basis of the conventional GM(1,1)model of grey system theory,the Divided Difference Unequal Interval GM(1,1)model of particle breakage was built and the related grey prediction software are developed.The influence of unit impact work,the number of compaction,the initial stacking height of sample and the particle shape on the particle breakage evolution regularity were studied.The stages of particle breakage were redivided and redefined,and the variation of the key indicators in the process of particle breakage were analyzed.The main research reslults are as below.(1)The Growth Path(GP)method was established.The famous and strictly self-similar Sierpinski gasket of fractal geometry was found in the ultimately two-dimensional fractal model obtained by the GP method.The ultimate fractal dimension(Ds)of the coarse-grained soil calculated by the GP method is 2.585,which is the same as the calculation result of the three-dimensional cataclastic rock model.When the actual size of the initial particle size fraction is inconsistent with the theoretical size,the size defect of the initial particle size fraction does not cause any error to the ultimate Ds calculation under the condition of rough calculation.(2)The unit impact work required for the particle size distribution(PSD)of spherical glass beads to reach the ultimate state was obviously higher than unit impact work required by the coarse sand.When the relative breakage(Br)was certain,Ds,glass beads were larger than Ds,coarse sand,because the degree of glass beads broken into finer particles was higher than that of coarse sand at the beginning of particle breakage.(3)The grey prediction model of percent passing by mass varying with compaction number under different conditions of unit impact work was firstly established.The grey prediction model of percent passing by mass changing with unit impact work and compaction number was secondly established in view of Ds equal to 2.585.The second model can be used to analyze the particle breakage produced by the compaction test and the lateral compression test(Static pressure).The grey prediction model of percent passing by mass changing with unit impact work,compaction number and initial stacking height was thirdly established.(4)With the decrease of initial stacking height,the percent passing by mass of coarse sand increases under the condition of the same compaction number and sieve diameter.The concentrated area of particle breakage of coarse sand in a compaction cylinder increases with the increase of initial stacking height.(5)For the coarse sand and glass beads with a single initial particle size fraction,the turning point of percent passing by mass varying with unit impact work of the newly generated intermediate particle size fractions can be obtained through the definite grey prediction model of particle breakage.The whole process of Br and Ds of coarse sand and glass beads varying with unit impact work was divided into four stages:Ⅰ,Ⅱ,Ⅲ andⅣ.The stage Ⅰ was the main stage of particle breakage.The four stages were defined as:Rapid,Fast,Slow and Creep breaking.The particle size distribution of two kinds of granular materials had obvious self-similarity from the beginning of stage Ⅱ.(6)During the breakage process,the largest particle size fraction generated by spherical glass beads produced more fines than coarse sand did.The change of initial stacking height had no effect on the variation of Ds with Br within the whole scope of the evolution regularity of the particle breakage.For coarse sand with angle,spherical glass beads and calcareous sand with higher degree of angle,the coefficient of curvature(Cc)varying with unit impact work was consistent.However,for the three kinds of granular materials,the coefficient of uniformity(Cu)changing with unit impact work was not consistent.Compared with Cu,Ds was more reasonable to indicate Br.