Elements of rock weakening of coal-bearing strata of the Canadian Plains Region

The Plains Region of Western Canada has coal-bearing strata whose strength is equal to or lesser than the coal. This is not common among coal basins throughout the world. The factors causing this are discussed. Diagenesis, along with the compressive strength of rocks, increases with depth of burial. Diagenetic effects, are limited or absent for the strata under consideration. The rocks consist of 90 percent very fine-grained sediments which have lower strength and elasticity than the remaining 10 percent of coarse-grained sediments. Clay minerals decrease rock strength with the strength reduction depending on the amount and type of clay minerals, and the natural moisture content. Stratification produces very large anisotropy because of the low bonding between individual rock layers. This, in particular, causes very low tensile strength of the rocks. Understanding the basic factors which influence rock strength is very important for the design of strata control and mechanization in underground coal mines.