Description of pillar behaviour at Heath Steele Mines

CIM Bulletin, Vol. 74, No. 834, 1981

GERALD A. ALLCOTT, Senior Engineer, and DONALD E. ARCHIBALD, Senior Geologist, Heath Steele Mines Limited, Newcastle, New Brunswick

Noranda's Heath Steele Mine is located 35 miles north of Newcastle in northern New Brunswick. Blasthole open stoping with partial delayed filling is the major mining method in use. The selection of slope and pillar dimensions to ensure mine stability was originally subjective. This paper describes the progress made in attempting to rationalize design.One major feature is the fracture pattern. The main orebody now being mined, the B zone, has undergone five periods of folding and each period of folding developed a family of fracture planes which are axial planar to that particular fold pattern.The other major features considered are the calculated increase in stress due to mining and depth and its relationship to measured strain. Experience has shown that ground problems affecting production have usually originated in rib pillars. Field observations of ground deterioration and multi-wire extensometer measurements of strain are tabulated together chronologically for each pillar.A factor representing stress and a common plane of weakness are identified. Graphical analysis is used to determine the effect of the plane of weakness on a typical stress/strain curve and provides a base for the design of pillars.
Keywords: Underground mining, Pillar design, Heath Steele Mines, Stoping, Fracturing, Rock mechanics, Stress, Strain, Viscosity, Structural geology.