DA Smith (formerly Agapito Associates, Inc.) has completed extensive underground exploration drilling, coring, in situ stress measurements, and geomechanical instrumentation programs at the three major underground coal mines in the North Fork Valley, Colorado since the late 1990's: West Elk (Arch Coal Inc.), Bowie No. 2 (formerly Bowie Resources, now Wolverine Fuels), and Elk Creek (Oxbow Mining, LLC).
Drilling was conducted in intake and return airways, including difficult-access active tailgate and bleeder entries where man-portable, permissible drills were required. Instruments installed included hydraulic borehole pressure cells (BPC), multiple point borehole extensometers (MPBX), roof sagmeters, roof-floor convergence stations, and datalogger systems. Instrument results provided valuable data regarding the onset of longwall abutment loads, pillar weighting, pillar core confinement, rib yielding, pillar floor punching, roof failure, and ground support response.
In situ horizontal stress significantly influences roof and rib control in the North Fork Valley mines. Findings from overcoring stress measurements are discussed in our technical paper:
“Implication of Highly Anisotropic Horizontal Stresses on Entry Stability at the West Elk Mine, Somerset, Colorado.” Proc. 24th Int’l Conf. on Ground Control in Mining, Morgantown, WV, 2–4 August 2005.