Comparison of Ground Support Systems - Essay Example

It is not only expensive but also time consuming to provide support for underground mining for the purpose of ground control that is essential for effective and safe contemporary mining. The most frequent kinds of rock support in practice these days include the combination of mesh screens and rock bolts and other different forms of shotcrete. Lately, innovative linings of spray-on polymer have been created to be used as a substitute type of rock support. Earlier researches have found that screen and bolt support is comparatively less expensive however it is not as effective as polymer linings and shotcrete are and also it is not even readily automated. In comparison to using screen and bolts, shotcrete is considerably more productive however it also is significantly more expensive and needs substantial amount of material handling. The material costs of spray-on liners are very much higher however they result in considerable increased productivity as well as lesser efforts for material handling in comparison to the other support systems. This report compares the productivity and economic factors linked with the shotcrete and polymer lining, bolt and screen underground rock support methods. It also discusses the direct and indirect production factors as well as the operating and capital costs, which include set times, installation, and material handling issues, for a generic mining operation. 1. INTRODUCTION Ground support has been employed in underground mines in order to ascertain the security and protection of the personnel as well as the equipment working there as well as to fulfill the desired engineering purpose of the aperture (Archibald, 1999). The rockmass around an aperture may be considerably fragmented and fractured as a result of the combination of stresses (in situ and induced), discontinuities and also, because of the blasting activities for the production or development purposes. Also, pieces of rock, that may range from a few grams to many tones in mass, may fall or slough into the openings of the mine as a result of gravity. Moreover, rock can be violently dumped into the mine openings because of the seismic bursting. The support methods have been developed in order to avoid the falling or ejection of the rock into the mine openings. Screen mesh, resin or mechanical rock bolts, and plain or reinforced shotcrete have been found to be the indispensable features of the production cycle of mining in Canada for year and have improved in the safety of the operator and the equipment along with enhancing the recovery of the minerals. Beginning from the late 1980's, Urylon Plastics Inc. (previously Guelph, Ontario) and in the present times, Mine guard Canada , in association with the Department of Mining Engineering at Queen's University and the MIROC - Mining Industry Research Organization of Canada created an innovative and new rock support system that is known as MIROC MineguardTM. MIROC Mineguard comprises of a thin, durable and highly flexible 2-component polyurethane spray-on liner. The RockguardTM is another polyurethane/polyurea hybrid liner, which has been developed by Futura Coatings Incorporation in Missouri, USA, has become available recently. MineguardTM and Rockguard™ are considered as the best forms of spray-on liners and both of them will referred as polymer liner support in this study. The other spray-on products under testing and development are Master Builder’s epoxy-based product and Fosroc’s latex-based Tekflex product. All systems have been demonstrated not only in the laboratory but also in the underground so that they may work in a various ways. The technical aspects and properties of every support system have been documented well in the literature. Each support system has some technical constraints and benefits, but they will not be included in detail in this study. Although being technically sound with respect to engineering concepts, however, it is also vital to take in to account that whether it is also cost effective or not, and that how each method effects the production cycle of the mining operations. This study will discuss and evaluate the primary costs related to the rock support systems that involve costs of labor, direct material, and equipment that are linked to each system as well as the delivery cost of that material. Then every support system will be evaluated in relation to its relative productivity. Moreover, this study will discuss the impact on support costs as a result of increased mine automation and increased depth of mining. 2. ROCK SUPPORT SYSTEMS According to McCreath and Kaiser (1992), there are three basic functions that are provided by a ground support system to the rockmass. These functions include retaining and holding of a broken rockmass together, providing reinforcement in order to assist the rockmass support (Hoek and Brown, 1980), and strengthening the rockmass in order to control swelling, and reducing the dilation and convergence of wall. Every support system can be employed independently on the basis of the engineering goals and mine environment. For permanent openings or in highly stressed areas, each of the support system may be employed in association with the other ground support system. On the basis of an industry survey in 1992 and according to the recent INCO operational data, the Table 1 given below briefly lists the important considerations for the corresponding support system. Variations in the costs of the material and application rates occur in relation to the experience of the operators as well as the selected support design configuration that includes length/spacing of the bolt, thickness of the liner, and opening dimensions. The “rock feature visibility” in the table 1 below illustrates the potential of personnel to evaluate the rockmass properties behind the support system (fragmentation, convergence, structural geology, bootlegs, etc.). TABLE 1: Support Considerations. (Espley, 1999) 2.1. Bolts and Screen The regular feature of Canadian mining has been the combination of rockbolts with wire mesh screen since about the 1940s. It comprises of a combination of welded-wire mesh and bolts that are grouted cables or mechanical-anchor, friction bolts, grouted dowels. The mesh is employed in order to retain loose rock whereas the bolts are employed in order to provide protection against structural wedge failure and stress-induced slabbing (Espley et al, 1999). On the basis of the ground conditions, rockbolts may be employed in an intermediary fashion or may be installed systematically to cover the walls and back of the openings at regular intervals, which illustrates the conventional tried and tested form of rock support that have been employed throughout the industry. A number of bolts and mesh can support a relatively large surface area in comparison to the volume of the material required for such a support. The support system can be employed either semi-automatically or manually with the help of standard equipment. Read More