1、翻 译 部 分英文原文IMPROVING ROCKBOLT INSTALLATIONS IN US COAL MINESA.J.S. SpearingI; B. GreerI; M. ReillyIIISouthern Illinois University Carbondale, IL, USA IIFrazer and Jones, Syracuse, NY, USASYNOPSISThe vast majority of the roughly 100 million rock anchors installed in mines in the USA each year use res
2、in cartridges1. About 4.5 million of these bolts are installed using a mechanical shell in addition to the resin to create an active (pre-tensioned) bolt. Over 1 million of the bolts are passive cable bolts and typically have an effective grout length of 1.2 m, regardless of the cable length, which
3、could be as long as 6 m. The successful performance of the resin grouted bolts depends on several parameters, including the annular gap between the bolt and hole wall, which should be relatively small, ideally from 3 mm to 5 mm. This requirement, combined with the high viscosity of the resin, produc
4、es a high back-pressure that can cause the bolt being installed to buckle or not be installed to standard. It is this back-pressure that limits the effective grout length with passive cable bolts and causes the mechanically anchored bolt failures (typically called spinners where the mechanical shell
5、 does not anchor). This creates potentially unsafe conditions and wastes time and money. A purpose, built rig was used to mimic underground installations and record the back pressures during full scale applications in the laboratory. This information was used, and is still being used, to reduce the
6、failures and sub-standard installations by producing improved designs. In addition, a flow model was calibrated that can act qualitatively to estimate the back-pressures and can be used as a crude screening process before full scale prototypes are built and tested. To date, the results obtained have
7、 been used to stop the use of a mechanical shell due to the proven higher rate of failures. A new, improved mechanical shell is being field tested and another system is under development. The use of the rig is therefore ongoing to develop improved mechanical anchor systems. It is too early for real
8、data; however, anecdotal evidence seems to indicate that significant improvements can and will be made.Keywords: Rockbolt, performance, mechanical anchor, resin, underground support, annular gap, installation pressure, back-pressure, resin ports.IntroductionCoal is key for energy production in the U
9、SA and is actively mined in 33 states. Approximately 90 per cent of this coal production is used to generate 50 per cent of the USAs electric power. Coal mining is responsible for over US $60 billion in annual revenue, and the industry directly and indirectly supports over 750 000 jobs in the US2. A
10、s Figure 1 shows, annual production has risen at a steady rate since 1960.In 2007, about 1.15 billion short tons of coal were produced from 1 438 mines. 612 of these mines were underground operations, and they accounted for about 31 per cent of the total coal produced3.Underground mining is of more
11、concern than surface mining when considering coal mine safety, for obvious reasons as roof and rib falls have the potential to cause serious or fatal injury to miners. The weak roof strata typically located above a coal seam are prone to skin failure, including massive failure in some cases. Over 1
12、500 roof falls occur every year in US coal mines4. In addition, however, the tight working conditions also make it easy for a miner to become pinned between a piece of machinery and the rib if proper safety procedures are not followed.2005 was the year when the least fatalities occurred on the coal
13、mines to date. In 2006, however, the coal mining industry was plagued by two major disasters; in January 2006 an explosion at the Sago Mine in West Virginia killed 12 people, followed in May 2006 by five miners being killed in another explosion at the Darby Mine in Kentucky. In August 2007, a furthe
14、r disaster occurred at the Crandall Canyon Mine in Utah in the form of a massive collapse, possibly caused by a coal bump, that resulted in nine miners being killed and a further three more fatalities during rescue operations.As a result of these disasters, Congress rapidly passed the Mine Improveme
15、nt and New Emergency Response (MINER) Act in 2006. The primary, relevant support-related provisions of this Act, according to the Mine Safety and Health Administration (MSHA), are: Each mine must develop and continuously update a written emergency preparedness plan, which must be recertified by the
16、MSHA every 6 months Mines must use equipment and technology that is commercially proven and available if it can improve safety Every mine must have 2 trained and experienced mine rescue teams capable of responding within 1 hour of an emergency if required Mine operators must report dangerous incidents and accidents to MSHA within 15 minutes or face fines of up to US$60 000 The criminal penalty cap will be raised to
