Failure-mode analysis of loose deposit slope in Ya'an-Kangding Expressway under seismic loading using particle flow code

Abstract

Particle flow code in two dimensions (PFC2D) was used to investigate the dynamic processes and hypermobility mechanisms of the loose deposit slope on the Ya’an-Kangding Expressway. The structure of the loose deposit slope is simulated by numerous balls that have different bonding strengths. A trial-and-error calibration and biaxial models were applied to determine micro-level parameters in PFC2D. The parallel bonds between particles, the velocity vector diagram, the displacement vector diagram, the porosity and the stress were analyzed in the numerical models. It was concluded that deep sedimentary basins can have large effects on the slope surface. Three different slip patterns were identified: sliding along the slope, collision of rocks in the down-slope, and breakthrough sandstone. The velocity vector diagram indicates that at the start, particles may move by falling, toppling, and sliding, but over time they begin to spread or flow. Particle location is a critical factor in the stability of loose deposit slope. Particle displacement is smaller at the top and center than at the bottom of the slope because the collision between the rock blocks involves momentum transfer, which causes the front of the mass to continue for a greater distance. The porosity of the surface slope generally increases with increasing seismic-wave loading time, while the porosity of the inner slope remains constant. The stress on the slope surface is much larger than that on the inner layer of the slope, indicating that seismic waves travel faster through hard rocks than through softer rocks and sediments.