Mining Contract: Leaky Feeder Mine Communications System

Contract Status & Impact

This contract is complete.

No final report was produced from this contract. For more information on this contract, send a request to mining@cdc.gov.

Under this contract, research and in-mine tests were conducted to investigate techniques for hardening and redundancy to make a leaky feeder mine communications system survivable, as described below.

• Hardening - Hardening involves improving the ability of the system cable and components to survive and to continue to perform after mine incidents. Some investigated techniques included cable installation methods, cable stress relief, burying or covering leaky feeder cable, component fire protection, and putting leaky feeder cable in conduit or integrating a messenger.
• Redundancy - For redundancy, after a mine incident occurs and communications are lost in the area, a miner can walk a short distance from the affected area and still communicate with the surface. Techniques investigated included a loop-around scheme with multiple base stations located at different surface locations, running independent leaky feeder cables in multiple entries, and using antennas and low-cost cables for coverage extension.

The resulting system design uses a Becker Mining Systems ultrahigh frequency (UHF) leaky-feeder communications system, enhanced dramatically to improve its post-accident survivability. The system was installed on a mine-wide basis at the Consol Energy Loveridge Mine for long-term evaluation. It spans an underground distance of 8 miles from the belt slope to the mining sections. Enhancement techniques included the following.

• Redundant loops to the surface - With a redundant loop, primary and secondary base stations are connected by overland, fiber-optic links, providing alternate communications paths to achieve redundancy. Two redundant loops, which utilize the belt slope and two airshafts, were used in the Loveridge installation.
• Redundant UHF trunks in parallel entries - Since access to the surface is not available beyond the most inby airshaft, redundancy was achieved by installing completely independent UHF leaky-feeder cables in parallel entries, one in the track and another in the belt.
• Coverage extension using low-cost cabling and antennas - With the redundant loops, communication coverage was extended to the belt entry by using a low-cost, VHF leaky feeder cable coupled to the main UHF leaky-feeder cable in the track entry. In addition, with redundant UHF trunks in parallel entries, communication coverage was provided in the parallel escapeway by placing antennas in that entry, alternately connecting the antennas to the track and belt leaky-feeder cables. This provides communication in the escapeway if either the track or belt entry leaky-feeder cable becomes non-functional.

Successful demonstrations were conducted for industry, labor, and government partners. Various failure modes were injected in the system to simulate mine emergency events. The system performed as designed, providing communication on either side of the simulated fault to the mine surface and between the two underground locations.