Hydraulic and earth engineering – Earth treatment or control – Rock or earth bolt or anchor
Reexamination Certificate
2001-11-23
2003-10-28
Lee, Jong-Suk (Department: 3673)
Hydraulic and earth engineering
Earth treatment or control
Rock or earth bolt or anchor
C405S258100, C405S259200, C405S259500
Reexamination Certificate
active
06637980
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
In an underground mine, providing and maintaining adequate support for the mine roof is of paramount importance. The majority of serious or fatal accidents occurring in underground mines in the United States over the years have resulted from an inability to control the roof of the mine. While accidents involving major cave-ins of mine roofs have become less prevalent over the years, it is important to note that a fatal accident can occur from the falling of even one large rock from the roof of a mine. Accordingly, mine roof control systems must be completely effective in order to provide safety for personnel working in the mines. The Mine Safety and Health Administration (MSHA) is empowered by the United States government to enforce mine safety standards, including roof support standards, and to provide inspection of mine roof control plans and practices carried out in the mining industry.
As a result of greater emphasis on safety and roof support, serious accidents involving major roof cave-ins have decreased substantially since the 1970s. In order to comply with MSHA standards, underground mines must have a roof control plan in place, and such plan will invariably include provisions for what is known as “primary roof support.” Primary roof support refers to abatement provisions designed to prevent a roof cave-in by effectively sealing the lowest layers of a mine roof to upper strata of rock. The most common and effective means for attaching lower level rock strata to upper layers is to utilize a roof bolt and epoxy resin to seal the various layers of rock strata. Roof bolts vary in length and diameter but are typically one-half inch or more in diameter and 30 inches to 12 feet long or longer in overall length. To place a roof bolt in a roof ceiling, a motorized roof bolter, such as that manufactured commercially by such companies as Fletcher Mining Equipment Company, is positioned in the front, unprotected face of the mine and features a drilling mechanism to drill several feet up through the mine roof. After a hole is placed in the roof, an epoxy resin in a pliable plastic tube is inserted in the hole. Next, a roof bolt is placed in the hole, and the placing of the roof bolt tears the packaging for the epoxy resin and mixes said resin to the bolt itself and the surrounding rock layers. The epoxy resin typically “sets up” or hardens within a matter of seconds and the bolt and rock layers are thereby sealed to each other.
In most underground mining situations, a roof bolt is placed approximately every four feet in the mine. Accordingly, placement of roof support is a major undertaking and a major source of expense for the mine operator. Despite the cost, roof bolt/epoxy combinations are the most effective and practical means for providing primary roof support, and fully meet the requirements promulgated by MSHA and various state enforcement authorities.
A number of prior art patents disclose and/or claim methodology for installing roof bolts in rock strata. These include U.S. Pat. No. 4,704,053 to Hipkins, U.S. Pat. No. 5,073,065 to Kleineke, and U.S. Pat. No. 5,417,520 to Rastall among others. U.S. Pat. No. 4,784,530 to Price, Jr. discusses the history of resin-based anchoring systems and identifies a number of other key prior art patents. Yet the prior art methods feature a number of serious drawbacks.
A key limitation to the effectiveness of resin-based systems is the presence of drawrock. Drawrock refers to thin layers of shale, one inch to twenty inches thick, which is frequently found throughout the United States immediately adjacent and above seams of coal. In such scenarios, as coal is mined, the immediate roof material may consist of several inches or feet of shale or drawrock.
Shale is typically very hard in the compressed state, and a mine roof characterized by shale usually is a very stable roof when the mine is first opened and the adjoining seam of coal first removed. However, when shale is exposed to the elements, i.e. moisture, the characteristics of the rock begin to change. Over a period of time, wet shale will begin to deteriorate into drawrock, and the layers of rock will separate. As this occurs, the lower, exposed layers will crumble and begin flaking off and dropping. It is quite typical that the inside of an underground mine will be wet, and often a substantial amount of water will be encountered. Accordingly, drawrock can be a major problem in a wet underground mine which is characterized by a shale roof or upper walls. While primary roof control is normally quite effective in securing various strata of rock together for three to six foot lengths, crumbling drawrock in the lower layer can undermine the protection.
A roof bolt properly anchored in an epoxy-based resin effectively supports the roof because it applies upward pressure to hold the various strata of rock together in an essentially compressed state. At the exposed end of the bolt, a base plate, typically 8 inches by 8 inches, is anchored against the roof by the bolt. This base plate supports the lowest roof layer while the bolt anchors the lower strata to upper strata of rock.
The presence of drawrock can seriously undermine a primary roof support system. If the immediate roof layer (just above the base plate) is drawrock, deterioration of the drawrock by environmental conditions can result in a crumbling of the roof in the vicinity of the base plate. Accordingly, the rock layer just about the base plate may crumble and flake away over time. When this occurs, the roof support system is compromised because in order for the system to be effective, the base plate must be applying pressure against the lower strata of rock anchoring them to upper rock layers. If drawrock crumbles in the vicinity of the base plate, the roof support system at that point consists only of a bolt in epoxy glueing the upper strata together. No pressure is being applied by the base plate. This may result in the lower rock strata becoming loose and falling.
State and Federal mine inspection officials are aware that the presence of drawrock can undermine a roof bolt support system in an underground mine. When the presence of drawrock results in a flaking away of the rock strata just above the base plate, inspection officials will require the mine operator to install another roof bolt or provide some other means for achieving primary roof support in that vicinity. For the mine operator, this is a very expensive problem, because it means the operator will have to bring a roof bolter into this area of the mine to install a new bolt. Since the drawrock deterioration may occur months or years after the installation of the initial roof bolt, roof bolters are typically nowhere near the area of the mine in which drawrock has created the need to re-install a bolt. The manpower requirements to move a roof bolt installation machine from remote areas of the mine back to areas previously mined may result in considerable downtime. However, the work has to be done because the drawrock damaged area of the mine is essentially devoid of primary roof support and the dangers associated with this condition are unacceptable.
The danger is even more pronounced considering that the older portions of the mine, where roof bolts were installed years earlier, are now typically passageways for access to new work areas of the mine. As such, it may be a major traffic thoroughfare for miners and equipment. A crumbling of the ceiling in this area, therefore, can result in a localized roof fall in a part of the mine more likely to affect personnel and equipment.
Prior art patents and methods have failed to appropriately address this problem. Those methods that have been so directed are generally ineffective or are too complicated to be practical. Perhaps the closest prior art to the present invention is found with U.S. Pat. No. 5,733,069 to Schofield, Jr. That patent discloses a re-tensioning apparat
Earl Products, Inc.
Lee Jong-Suk
Waters Robert R.
Waters Law Office PLLC
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