Experimental And Numerical Simulation On Performance And CBR Of Graded Macadam Base Of Expressway

As the flexible base layer of the expressway,the graded gravel has a positive preventive effect on alleviating the road frost heaving and typical reflection cracks in the seasonal frozen area.Because the graded gravel is a typical bulk material,the angularity has a great influence on its mechanical properties.Therefore,when the mechanical properties are numerically simulated,the conventional discrete element model is difficult to accurately and accurately simulate the mechanical properties of the graded macadam.In order to find the basic gravel material and grading type with better macroscopic mechanical properties,this paper uses the rolling resistance model to carry out numerical simulation and laboratory test on the mechanical properties of the graded crushed stone.Based on the sufficient survey about the study on the performance of graded broken stone at home and abroad,the rationality of graded broken stone is analyzed and verified from the perspective of the combination of indoor CBR test and numerical simulation.According to the national standard,a comparatively reasonable type of gradation is designed with the combination of maximum density curve and discontinuous gradation curve model,and the rationality of this gradation type is verified by bailey method.According to the gradation obtained,an angle of repose experiment is carried out first,and then,PFC2 D is applied to simulate the angle of repose experiment to calculate the corresponding coefficient of friction and coefficient of rolling friction under different gradations.A numerical model of CBR test is established to compare with the actual CBR laboratory test results by bringing the known mechanical parameters of the raw material into the model,and the influence rule of gradation type on CBR value is explored under the premise of ensuring reliability,and the corresponding gradation of large CBR value is found by modifying the mass fraction of each particle size aggregate in the model for many times.The conclusion is drawn through experiment and calculation: The larger the Particle size of crushed stone aggregate is,the larger the angle of repose will be,and the larger the corresponding coefficient of friction will be,and meanwhile,the successive type and average particle size of gradation will also affect the angle of repose;the coefficient of friction and coefficient of rolling friction are also positively correlated within a certain range of particle size;In the numerical model of CBR test,different mechanical parameters of materials have great influence on the results,in which the stiffness ratio and CBR value are positively correlated;the proportion of different coarse and fine aggregates also has a great influence on the CBR value.At last,the reasonable recommended value of the gradation about gravel aggregate is given by synthetically analyzing the data,which is only for reference.