The room and pillar design for underground limestone mines adopting hydrogeological properties of the fractured rock masses

Limestone is one of the major mineral resources in Korea, and the application of underground mining methods is expanding for obtaining high-grade ore and also for settling the environmental issues. An experimental program has also begun focusing on the carbon resources recycling technologies at underground limestone mines through the joint efforts among research institutes and universities. Hence, development of the suitable limestone mine site characterization system is one of the major concerns for field engineers in Korea. Engineering characteristics of the fractured rock masses containing joints and faults are significantly controlled by the hydrogeological conditions resulting from the groundwater flow and affects the overall stability of the mine openings. One of the key factors for the safe and efficient mining operations is to design the most suitable layout of the room and pillars, with relevant hydro-mechanical characteristics of the fractured rock masses around the underground mines. The groundwater flow and resulting pore-water pressure within the rock mass should be considered for the effective stress stability analyses and, also for designing proper de-watering systems. Prediction of the groundwater inflow requires a detailed knowledge of the geologic conditions. The effect of the water pressure should be considered to assess the stability of underground openings, in terms of the factor of safety and the yield zone size within the rockmass.

In this study, some numerical codes are adopted to construct the hydrogeologic model of a undeground limestone mine, and the rate of groundwater inflow and resulting porewater pressure distribution were estimated. Three-dimensional stability of the mine openings is also analyzed using the effective stress developed within the rock mass. Finally, a guideline for designing the room and pillar layout is provided, based on the variation of the safety factor with the width-to-height ratio of the mine openings.