Seepage and stability analysis of pore air pressure on a high-bench dump under heavy rainfall

Under heavy rainfall, the pore air pressure in the unsaturated zone of a dump hinders rainwater infiltration in loose soil, which further affects the safety and stability of the dump. However, traditional analysis methods often regard pore air pressure as atmospheric pressure and ignore its impact on dump safety. Relying on the high bench dump project of a copper mine in Jiangxi, basing on the field test and survey results and combing with the horizontal slice of a typical dump profile, the seepage law and safety stability of a high bench dump with traditional methods while considering the pore air pressure were analyzed. Moreover, the influence of pore air pressure on a wet front, pore water pressure, and slope safety factors of high bench dump under heavy rainfall conditions were discussed. The research results show that pore air pressure at the initial stage of rainfall infiltration is not significant, and pore air pressure does not have a direct impact on the stability of the high bench dump. However, as the rainfall continues, the effect of the pore air pressure begins to appear, reducing the infiltration rate of the high bench dump. Further, the downward movement speed of the wetting front becomes slower, the pore water pressure rises slowly, and the influence of the heavy rainfall delays the stability of the high bench dump. In the middle of rainfall infiltration, the pore air pressure remains constant, the delay effect varies, and the penetration depth increases. In the late stage of rainfall infiltration, when the wetting front moves down to the critical plane of the layering, the pore air pressure balance is destroyed, continuing to increase to a new constant value, which increases the impact on the high bench dump. When the traditional method of wetting front and considering the pore air pressure of wetting front move down to the same depth, the safety factor of the high bench dump under the action of pore air pressure is obviously reduced. The research results provide a theoretical basis for long-term safe operation and disaster monitoring and early warning of high bench dump under heavy rainfall conditions.