Stress analysis and optimization of coarse aggregate of large stone porous asphalt mixture based on discrete element method

The content of fine aggregate and asphalt in large stone porous asphalt mixture (LSPM) is low, and the load is mainly borne by the stable skeleton structure formed by the interlocking between coarse aggregates. The stress state of coarse aggregate in LSPM is an important factor affecting the bearing capacity of LSPM. The two-dimensional discrete element model (DEM) of LSPM is established by discrete element method. In order to simulate the true profile of the aggregate surface and ensure the formation of a stable embedded extrusion model, the spherical particles of coarse aggregate with a particle size greater than 2.36 mm are replaced by irregular particles. The virtual bearing plate test was carried out on 6 LSPM rut plates with different thicknesses. The force chain network inside LSPM was quantitatively analyzed by five indexes: force chain number (FCN), force chain evaluation coefficient (FCEC), simplified value of force chain angle (SFCA), angle stability coefficient (ASC) and force chain strength (FCS). When the thickness of the DEM is greater than or equal to 7.5 cm, an integrated skeleton structure is formed inside the LSPM. The bearing capacity of asphalt treated base-25(ATB-25), asphalt treated base-30(ATB-30) and LSPM is compared by virtual bearing plate test under this thickness. The ability of LSPM to bear heavy load is stronger than that of ATB-25 and ATB-30. The overall deformation under heavy load is about 18.4% of ATB-25 and about 29.6% of ATB-30. In the process of bearing load, the contribution rate of embedded force between aggregates in LSPM is large. When the aggregate particle size is greater than 9.5 cm, the average pressure of the aggregates in LSPM is greater than the average pressure of the aggregates in ATB-25 and ATB-30. In order to avoid the crushing of LSPM coarse aggregate due to excessive force, which affects the skeleton structure and bearing capacity of LSPM, 26.5 mm sieve is determined as the key sieve to improve the stress state of LSPM coarse aggregate. In the recommended gradation range of LSPM, the passing rate of 26.5 mm sieve is adjusted, which effectively improves the stress state of coarse aggregate and ensures the stability of LSPM bearing capacity. The recommended pass rate of 26.5 mm sieve of LSPM is 86%.