Longwall mining under the ocean at Cape Breton collieries

Abstract

Cape Breton is an island at the northeastern extremity of mainland Nova Scotia on Canada's eastern seaboard. The Sydney Coalfield, located on the east coast of Cape Breton, is part of a large carboniferous basin beneath the Atlantic Ocean between the shores of Cape Breton and the province of Newfoundland. The coalfield is Pennsylvanian in age and contains the largest coal reserves in Eastern Canada. More than 98% of the coalfield is submarine. Cape Breton Development Corporation (CBDC), a federal Crown corporation, currently operates two underground coal collieries, Lingan and Prince, producing nearly 2.5 million tonnes of saleable coal and has under development two new collieries, Phalen and DonkinMorien. All currently operating and planned collieries are 'slope collieries'. While room and pillar mining has been practised at shallower depths in the past, all current workings are based on 'U' layout longwall (advancing at Lingan and retreating at Prince) system with full caving. In designing submarine workings, the major concern is the prevention of ingress of seawater consistent with optimal extraction of resources. Guidelines based on experience and engineering are established for partial to full extraction. The important guideline followed in the Sydney Coalfield is that the strain at the seabed should not exceed 8.5 mm/m as the result of extraction. The longwall faces are fully mechanized with ranging double drum shearers, armoured face conveyors and twolegged hydraulic shield supports. Roadheaders are deployed in maingates. The coal is transported to the surface by a system of belt conveyors whereas men and materials are transported by a rope haulage system in the slopes and by diesel locomotives in the maingates. Because of the submarine workings, mine openings cannot be at the desired location. Hence, efficient layout from the point of view of optimal extraction of resources is not feasible. As the mine progresses, the length of ventilation circuits and transportation distances for men and materials increase. This results in the requirement of higher ventilation pressures and reduced effective shift working time which contribute to higher costs and lower productivity. Efforts are being made to overcome these shortcomings by the introduction of advanced technology in all aspects of operations: ventilation design by computer simulations, methane control by crossmeasure borehole drainage, environmental monitoring by computerized remote monitoring system and reduction in.travel time by highspeed haulage system are a few of these aspects.