Primary roof and rib control of underground openings is traditionally accomplished by metallic supports that may have a variety of configurations. Perhaps the most common are steel roof and rib bolts, which are generally spaced on a regular pattern within the roof, and sometimes ribs of the entry. These primary support devices are intended to prevent catastrophic failure of the openings. They are generally not suited to prevent spalling between their isolated locations. Tensar International Corporation offers a heavy-duty polymer geogrid to provide supplemental roof and rib skin control.
Research & Testing
The National Institute for Occupational Safety and Health (NIOSH) Mining Pittsburgh Research Laboratory (PRL) in Pennsylvania is dedicated to testing products and facilities to eliminate mining fatalities, injuries and illnesses. They have been conducting research and prevention activities since 1910.
In July 2007, NIOSH PRL conducted load displacement tests on Tensar® UX3326-45 Geogrid in simulated loading conditions related to the performance of screen and mesh when used for surface control in underground coal mines. They reported the UX3326 Geogrid’s strength to be 86% compared to 8-gauge, steel wire using 6 in. by 6 in. plates on a 4 ft by 4 ft pattern.
It should be noted that a 20% increase in strength was witnessed when 8 in. by 8 in. plates were utilized at the corners and a 100% increase in strength was
observed when mild, steel “bacon strips” were used in the rib–rib direction.
Durability & Safety
Designed to replace 8-gauge, welded wire, 4 in. by 4 in. roof mats for secondary control of roof strata between roof bolts, Tensar UX3326 Roof Mats are an integrally formed structural geogrid for underground mine and tunnel applications, that provide greater skin coverage for less fall through by small rocks. They are easy-to handle and safe to work with since they are lightweight and lack sharp edges. The result is increased production efficiency and decreased injury downtime.
The flame-retardant additive is injected during the batching stage of production and complies with the Mine Safety and Health Administration (MSHA) CFR30, Part 7, for permanent installations. Further, the polymer grid structure will not corrode in a damp environment and is totally impervious to acidic conditions.
Other unique properties of UX3326 Geogrid include:
- Inby-outby stiffness for production installation from miner/bolters
- Rib-rib flexibility allowing continuous roof-to-rib reinforcement for securing entry corners
- Strength equivalent to 8-gauge, welded wire modules, but 1 /7 the weight
- White, reflective color for increased entry brightness