The present invention pertains to the field of secondary support for subterranean mine tunnel roofs. More particularly, the present invention pertains to support members and systems used to help support mine roofs and prevent collapse of the roofs into the excavated tunnel.
Mining operations typically involve excavating tunnels with rectangular or square shaped cross sections, with a roof portion perpendicular to the ribs. Ribs are the supporting side walls of the excavation. The roof of the tunnel must support the weight of all the strata across the open tunnel span.
Since the earliest days of mining, cribs, rectangular blocks traditionally made of hardwood, have been used as secondary support for the roofs of mines. Crib is a term of art in the mining industry, and refers to both the individual blocks stacked to form a support column and the finished support column itself, and is derived from an old Wales mining term meaning to lay at right angles to each other as in a foundation, which describes the traditional construction method for forming a support column. The traditional use of hardwood cribs was inspired by the waste products of the sawmill industry, where discarded centers of logs sawn into planks were plentiful, cheap, and uniform in size and shape.
Unfortunately, traditional cribs have many significant drawbacks. Hardwood cribs are susceptible to rot and insect attack, and while uniform in shape and size, no two cribs have the same strength characteristics because they come from different trees grown in variable conditions. The cribs are subject to swelling and shrinkage, depending on the humidity inside the tunnel. The lack of uniformity in the strength and the varying rot/insect resistance of each crib result in unpredictable strengths and unknown longevities of any given support column. Given the way in which the support columns are constructed, a rotted or otherwise strength compromised crib can only be replaced by unstacking and rebuilding the support column, a time consuming and potentially dangerous activity. Usually, the mine atmosphere dries the water from the wooden cribs, shrinking them, and breaking the support connection with the roof.
Installation of a support column made of cribs is usually a tedious and labor-intensive process, as a standard eight foot high roof requires anywhere from 20-25 stacked cribs, and the cribs must be carried in by hand and stacked manually to form the support columns. Also, as the cribs are simply dry-stacked on top of one another, any lateral movement of the roof tends to dislodge the uppermost cribs, causing the entire support column to fail and potentially resulting in a roof collapse and death or injury to individuals working inside the mine. Another problem with the traditional hardwood crib support column is that its construction results in both visual and airflow obstructions resulting in increased pressure requirements to circulate the air. As with any wood product, the support columns are highly combustible, another potential danger inside a subterranean tunnel.
More recently, with demand for hardwood high, the price of hardwood has been increasing, and the availability of hardwood for crib material has been decreasing, further eroding the attractiveness of the traditional crib.
What is needed is a crib that is lightweight and easy to install, requires no special tools or training for installation, and when installed, provides superior strength and reliability in mining applications.
The invention is an improved crib or support member, a method for constructing a support column system using the improved support member, and a support column resulting from the method using the improved support member, the support member comprising a beam having two opposed ends, each end affixed to one of a pair of bearing members held in spaced apart relation by the beam, each bearing member having a top surface and a bottom surface, the top surface further formed with a male coupling structure and the bottom surface further formed with a female coupling structure adapted to receiving the male coupling structure. The support column system is comprised of stacked sets of support members, in a typical embodiment each set comprising a pair of support members, the first set of support members laid with the bottom surface adjacent to the floor of the tunnel, the support members in parallel spaced apart relationship to one another. A second set of support members is placed on top of the first set, but with the beams of the second set turned 90 degrees in relation to the first set, and with the female couple structures of the second set receiving the male coupling structures of the first set to lock the two sets of support members together to form a column with a square lateral cross section and a hollow interior space. Additional sets of support members are stacked in this fashion until the top set contacts the roof of the tunnel, thus providing secondary support to the roof.
The features and advantages of the invention will become apparent from a consideration of the subsequent detailed description presented in connection with accompanying drawings, in which:
The following is a list of reference labels used in the drawings to label components of different embodiments of the invention, and the names of the indicated components.
The inventor uses the term support member here to mean an individual block or crib, and support column to mean a series of cribs or support members stacked to form a secondary roof support column.
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The support member 100 is typically constructed of a structural polyurethane material that is poured or blown into forms. In some embodiments, the support member may formed from a mix of polyurethane and another material such as metal mesh, cardboard, wood dowels or fibers. The material used to form the support members is ideally strong, uniform, lightweight, and fire resistant compared to a similar sized hardwood crib. Compared to a typical hardwood crib, the support member according to the invention is about 75% lighter, and about 100% lighter compared to a concrete stacking oval as known in the prior art. The “dog bone” or “dumbbell” shape of the support member as shown in the Figures, reduces the overall weight of the support member 100, as well as permits light and air circulation through a constructed support column 200. The “dog bone” shape also allows for faster and easier handling of the support members and construction of the support column 200, as it allows the support member to be picked up, by the beam, with one hand, instead of using two hands to pick up a traditional rectangular shaped crib.
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It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the scope of the present invention.
Reference is made to and priority claimed from U.S. provisional application Ser. No.61/726,746 filed on Nov. 15, 2012.
Number | Date | Country | |
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61726746 | Nov 2012 | US |