The largest coal reserves in Brazil are located in the state of Rio Grande do Sul, however the South Catarinense Carboniferous Basin concentrates the largest number of coal underground mines in the country. CIENTEC conducted studies on sedimentary rocks present in the enclosing layers of the Barro Branco coal seam. The samples were collected through vertical boring, using a double tube core barrel (NX diameter), and submitted to macroscopic petrographic analysis, physical and mechanical laboratory tests to determine the strength and deformability of different rock materials. The results allowed the characterization of the different sedimentary rock types enclosing the Barro Branco coal seam. These resistance patterns are used for the analysis of the carrying capacity of the host rocks and design of the coal pillars, when the room and pillar mining method is used.
In the 1990s, CIENTEC - Foundation for Science and Technology of the Rio Grande do Sul State, conducted pioneering studies in Brazil related to coal mining, in order to establish a methodology for pillar design for underground coal mines in southern Brazil (Zorzi 1990, 1996). The activities in these projects included detailed studies in laboratory for the geomechanical characterization of the materials present in the host rocks of the Barro Branco coal seam, the main mined underground coal seam in the South Catarinense Carboniferous Basin.
The purpose of the laboratory tests was to determine the mechanical behavior of the host rocks at the immediate roof and floor of the coal seam. In this context, the first 5 m above and below the coal seam comprise the portion of the rock mass that is under the greatest redistribution of stresses due to excavation. This area of the rock mass is where the gallery support systems are applied. In Brazil, the roof bolting system is the most used one, which is based on the suspension effect and/or friction or beam-building effect mechanisms (Peng 1986).
On the other hand, when dealing with the design of coal pillars, one cannot forget the role of the host rocks, as the foundation responsible for the support of the loads transmitted by the pillars. The coal pillar design method recommended by the DNPM - National Department of Mineral Production, the official Brazilian department responsible for the oversight of mining, includes in its concept the analysis of the carrying capacity of the host rocks (Zorzi et al. 1991).
This study presents the procedures adopted for the geomechanical characterization of the host rocks of the Barro Branco coal seam, mined in the South Catarinense Carboniferous Basin in southern Brazil. The obtained results were statistically processed and allowed the characterization of the main lithologies in the host rocks of this coal seam.