Mining Contract: Development of a Seismic System for Locating Trapped Miners

Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

The overall objective of this contract was to more fully evaluate the capabilities of the SureWave Technology’s seismic system for locating trapped miners at two different field sites. One major goal in this project was to determine the depth capability of the system and other goals of the project were to evaluate the system under various “difficult” (but not uncommon) mining situations.

Field test #1 of the SureWave seismic system was performed in June, 2012, at a shaft site on the surface approximately 1,140 ft above an active Pittsburgh Seam longwall coal mine in Northern Appalachia. The surface site overlaid a 10-entry 900-ft-wide by 1,200-ft-long section of the mains heading to the active longwall. In general, this first site was considered fairly noisy and the surface was covered with considerable soil and fill material.

Field Test #2 was performed in November, 2012, at an isolated, heavily wooded hillside with depths ranging from 450 ft to 1,700 ft above an active Owl Seam room-and-pillar coal mine in Eastern Kentucky. The surface site overlaid a 6- to 7-entry, 550-ft-wide by 3,300-ft-long section of the mains headings to the active mining sections. In general, this second site was relatively quiet and bedrock was exposed on the surface in many locations.

During the field testing, the maximum depth capability of the SureWave system was bracketed to be between 1,175 ft and 1,525 ft (at quiet Field Site #2). At the 1,175-ft depth (with the sensors on bedrock), the system clearly detected about 20% of the known pounding cycles, while at the 1,525-ft depth (with the sensors mounted through the topsoil), the system did not detect any pounding cycles. This depth limit was further supported by the testing at Field Site #1. With 1,140 ft of depth, a noisy environment and poor soil for mounting the sensors, the miners’ pounding was detected at only 2 out of 7 underground locations and during only 2 out of 18 pounding cycles.

Also, the horizontal offset capabilities of the SureWave system were demonstrated during the field test. At Field Site #2, at 575 ft of depth, the system strongly detected signals up to a horizontal offset distance of 890 ft (57.1°), and at a depth of 750 ft, the system strongly detected signals up to an offset distance of 580 ft (37.7°).

During the field testing, the variance of the coupling of the sensors to the ground vibrations was documented. A sensor placed just under the sod was found to be non-responsive to seismic signals, while a sensor simply placed at the bottom of a 2-ft deep auger hole was found to be only 60 to 80% as sensitive as a sensor mounted on a stainless spike at the bottom of an adjacent 2-ft deep auger hole. Even when the sensors were mounted on apparently equivalent bedrock, the strength of the detected signals between the sensors was often found to be significantly different.

Also, the underground location and tool used to pound was documented to be critical to successful detection of the seismic signal. Over a series of pounding cycles, the observed signal strength generated by using a crib block to pound on the roof rock averaged 180% stronger than the observed signal strength generated by using a sledgehammer. Further, a very large difference in the ability of specific underground pounding locations to transmitting the pounding energy was documented. At two underground crosscuts, only 1 out of 46 attempts of the miners’ pounding signals were transmitted to the surface, while at an adjacent crosscut, 18 out of 26 attempts transmitted detectable pounding energy to the surface.

Ultimately, as the final conclusion of this project, the SureWave system would be confidently recommended to be used to detect trapped miners at depths less than 1,200 ft.