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Technology News

From the Bureau of Mines, United States Department of the Interior

Technology news describes tested developments from Bursau of Mines programs. it ie published te encourage the
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No. 433, April 1994

Resin-Grouted Cables for Enhanced Coal
Mine Roof Support

Objective

Develop an easy-to-use, reliable, resin-grouted cable
support system capable of being installed as primary and
secondary roof support in coal mines.

Background

Primary and supplementary support of coal mine gate
roads has become an area of great interest as coal produc-
tion from advanced longwall technology has increased in
the United States. Variations in geology, stress conditions,
and mining geometries all affect support selection deci-
sions. With the goal of improving mining safety, the U.S.
Bureau of Mines (USBM) is investigating the use of cables
as a support option for longwall gate roads,

Previously, the most common type of supplementary
support was wooden cribs, Cribs can provide significant
reinforcement capacity over a large deflection range.
However, crib support systems restrict the flow of air nec-
essary for the ventilation of the workplace, generate unac-
ceptable floor heave, and permit large roof deformations
that can lead to failure. Additionally, the placement of
wooden cribs or posts accounted for 905 injuries in 1993,
approximately 5% of all underground accidents that year.
The lack of an adequate supply of timber has also elevated
the pricing structure and created some shortages.

How They Work

Cable supports are composed of multistrand wires that
are anchored into the mine roof with slightly modified

resin formulations. Because they are flexible, the cables
can be easily installed into holes much deeper than the
height of the opening. Cables also have a high load-
carrying capacity, 258 kilonewtons (58,000 pounds force),
and the reinforcement mechanism is similar to that of
resin-grouted roof bolts, Rock is strong in compression
but weak in tension, and most roof failures are caused by
tensile failures of the rock. Cable bolts act to decrease the
tensile forces, which reduces the potential for roof failure.

As a supplementary support system, cable bolts have
several advantages over wooden cribs, They reduce the re-
sistance to ventilation by approximately 25%, which per-
mits higher volumes of air at lower velocities and helps to
minimize suspended rock and coal dust. The use of cable
supports can also reduce the material-handling injuries
related to the placement of wooden cribs, since cables are
much lighter and are easy to install.

Test Results

Four massive test areas have been established in coal
mine gate roads using high-strength seven-strand cable
bolts as supplementary support, and the resulls have been
extremely favorable. The immediate roof of the tailgate
entry was maintained as the retreating longwall passed the
test area. Cable supports were also used to stabilize
bleeder entries, longwall setup rooms, longwall recovery
shoots, and difficult intersections. A typical geologic cross
section is used to select the cable support and resin-grout
lengths, as shown in figure 1, A coal minc tailgate sup-
ported with resin-grouted cable supports and subjected to
the stresses and subsequent loads associated with first and
second panel mining is shown in figure 2.

This document was prepared by the US. Burceu of Mines. Neither the United States Government nor any person acting on behalf of the United
States Government assume any liability resulting from the use of the information contained in this document, of warrants that such use be free from.

privately owned rights.



Cable supports may not be the support of choice in
every supplementary support situation. More research will
be conducted to study the rock-support interaction mech-
anism to develop safe cable bolt reinforcement parameters
and designs.

For More Information

Addition information can be found in "Cable Bolls for
Longwall Gate Entry Support," by S. C, Tadolini and J. L.
Gallagher, a paper in “Technology for Longwall Ground
Control," USBM Special Publication 01-94.

[sity state

Mudstone

ZZ Gaal
Simplified
geclogie
column

Figure 1.—Typical coal mine Intersection column used for
designing cable holt length and resin-grout length.

Currently, two manufacturers provide system compo-
neats for resin-grouted support systems used in the USBM
underground investigations. For product information and
material availability, contact

Stephen C. Tadolini

Denver Research Center

US, Bureau of Mines

Denver Federal Center, Building 20
Denver, CO 80225

Telephone: (303) 236-0751

Fax: (303) 236-0828

Figure 2.—Gate road supported by resin-grouted cable has
already been subjected to first panet loading. Panel 2 Is approx-
imately 60 meters (200 feet) inby this location.

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