Coal pillar design for longwalls under the ocean

Abstract

Coal pillar design in longwall mining must balance the need to ensure roadway stability with economic extraction of reserves. In particular, the design must accommodate the effects of stress redistribution providing stability not only during roadway formation but also by the extraction of longwall panels. There are four types of pillars usually involved, as illustrated in Figure 1, namely: Pillars between main access roadways; Pillars between access roadways and a longwall panel (start/stop pillars); Pillars between adjacent longwalls (rib pillars); Boundary pillars between adjacent mines. This paper outlines the approach of the Cape Breton Development Corp. (CBDC), Nova Scotia, Canada, to meeting the challenges of designing pillars in modem longwall coal mining under the North Atlantic Ocean. In addition to complying with regulatory requirements, other influences must be considered, such as: Protection from interaction effect of working other seams; Protection of the seabed by maintaining strata mass integrity. After discussing the mainly empirical, current practices in pillar design, two longer-term strategies are discussed: (1) pillar reduction (smaller sizes), where appropriate, and (2) elimination of rib pillars completely, where possible. A key feature in developing these strategies is an innovative research and development program run jointly by CBDC and CANMET's Cape Breton Coal Research Laboratory (CBCRL). Several projects are summarized involving development of appropriate geotechnical monitoring and numerical modeling procedures.