Effects of particle gradation and vibration intensity on the pore water pressure response of sandy mine waste*

Abstract Rainfall infiltration and heavy mine-truck traffic can promote pore-pressure build-up and reduce waste-dump stability. Shaking-table tests of four river-sand/quartz-sand mixtures examined the effects of gradation and vibration intensity on the pore water pressure response of sandy mine waste specimens prepared by underwater deposition. Coupled SEEP/W-QUAKE/W-SLOPE/W analyses evaluated engineering-scale response, and SLOPE/W calculated factors of safety using the Morgenstern-Price method. During the first vibration, pore pressure generally increased with acceleration. During the second and third vibrations, peak response varied non-monotonically as prior loading altered density and compressible pore space. Several high-acceleration cases reached or approached the common pore-pressure reference level used for cross-condition comparison. Relatively uniformly graded LS1 (100% quartz sand) was more sensitive to pore-pressure build-up, whereas LS3 (25% quartz sand and 75% river sand), with a relatively broader particle-size distribution than LS1, tended to stabilize during later stages. In the LS3-equivalent numerical case, traffic-induced loading concentrated excess pore pressure near the crest platform, slope shoulder, and shallow slope surface under the prescribed water-table and infiltration conditions. Increasing the peak load from 20 kPa to 100 kPa expanded the high-pore-pressure zone and reduced the minimum factor of safety from 1.30 to 1.25 (3.54%). These results indicate that rainy-season stability assessments should consider both sandy-waste gradation and traffic-load intensity.