| Popis: |
Resin-grouted rebars now account for about one-third of all bolts installed annually in U.S. coal mines. Although resin bolts provide superior roof support compared to mechanical anchors, they are expensive, toxic, and flammable. The bolting operation itself is a bottleneck in most mines, while installation of bolts is one of the most hazardous jobs underground. In the United States, innovations in roofbolting systems are being made in three principal areas — productivity, safety and cost. The problem of improved safety, increased productivity and lower bolting costs has been addressed through the development of lower cost cementitious materials for grouted bolts, in a versatile bulk-storage and injection system. This novel system was initiated by the U.S. Bureau of Mines and further developed by Terra Tek, Inc. for automatically drilling the hole, mixing and injecting an extremely fast-setting and high-strength inorganic grout, and installing a headed rebar — at substantial cost savings and productivity improvement over conventional methods, while maintaining the safety achieved with resin bolts. Laboratory and field pull-test data, in three minutes after placement, have shown the cement to develop strengths about a third higher than with resin bolts, along with a stiffness from over two-thirds to twice that of the fastest setting resin available. Cycle times are shorter than for a conventional resin system, and thereby expected to result in about a 10% productivity improvement. The paper describes the bolting system, and results of short and long-term pull-tests in the laboratory and field. Economic and productivity gains achieved in comparison with conventional bolting are also presented. The configuration of the components lend themselves to full automation and remote operation. In low seam mines this system can be combined with the “flexible drill” and “bolt-bender-inserter”, two devices also developed under U.S. Bureau of Mines' sponsorship. The application of this system to low seam mines is discussed, along with its impact on improved roof control and safety. |
