Gradation Design of Phosphorus Tailing–Graded Waste Rock Subgrade Filling Using Discrete Element Method

Abstract

The method of using silt phosphorus tailing instead of traditional sand and filler as sub-grade filling has been suggested to greatly improve the comprehensive utilization of solid waste phosphorus tailing. A suitable combination of phosphorus tailing and graded waste rock can be adopted to improve the stability of the structure of filling, which can then improve the soil properties of phosphorus tailing and prevent the formation of quicksand and landslides. In this research, a discrete element model was established by combining a graded mixing method and the concept of equivalent particle size, and the discontinuous gradation design of a phosphorus tailing–graded waste rock mixture was carried out. Using the filling coefficient, different structural types of mixture composition were verified, and the California Bearing Ratio was used to test and analyze the specimens with different mixtures, grading, and structural type. The results show that the porosity of the main skeleton calculated with the model established using the discrete element software Particle Flow Code and the porosity obtained with the tamping test fit well, with the minimum porosity of the optimal main skeleton coarse aggregate being 30.44%. At the same time, by analyzing the effect of filling the porosity of graded waste rock with different mass fractions of phosphorus tailing and by determining the California Bearing Ratio of the corresponding filling structure, it was shown that the skeleton-dense structure with the best gradation of the mixture displayed better road performance and that the phosphorus tailing–graded waste rock system with improved performance can be used as subgrade filling or in the preparation of pavement base material.