High safety pillars design for underground excavation of natural stone blocks

Abstract

In existing underground mines of dimensional (natural) stone in Slovenia, including the Lipica II and Hotavlje I quarry, the geomechanical characteristics have been observed concerning safety pillars with a low width-to-height ratio. The initial height of safety pillars usually amounts to 4.5 m, but with deepening of underground spaces it increases by 3.0 m; in places, it may reach values of up to 25.0 m or even higher. In previous years, special attention was paid to the installation of stress-strain systems for controlling the planned dimensions (width and height) of large open underground spaces (rooms) and the dimensions of high safety pillars, along with continual monitoring and identification of instability phenomena in the ceiling and sides of large open spaces (rooms). The paper presents procedures for the planning, optimization and monitoring of high safety pillars for underground excavation of natural stone blocks. Key words: Natural stone, high safety pillars, room-and-pillar mining method, underground mining, quarry.