Geotechnical Evaluation and Longwall Feasibility
AAI performed geotechnical and economic evaluations for the feasibility study of longwall mining at the Trapper Mine for Mencon, LLC. A geotechnical evaluation was conducted for the purpose of (1) identifying geotechnical hazards to longwall mining and (2) establishing geotechnical parameters for mine design. The tasks of the geotechnical program comprised:
- Review and summary of the existing geological/geotechnical database,
- Laboratory testing of rock mechanical properties,
- Measurement of in-situ horizontal stresses,
- Assessment of geotechnical conditions and hazards concerning underground mine feasibility, and
- Establishment of geotechnical parameters for longwall mine design and cost estimating.
The economic evaluation of longwall mining included evaluation of mining horizons, longwall panel width, panel orientation, gate-road pillar dimensions, ground support and impact of faults. AAI also provided highwall mining design guidelines for Trapper, and a highwall mining test area has been successfully mined.
In 2006 the Trapper Mine was the site of one of the largest slope failures in Colorado. A mass of rock approximately 170 acres, 120 feet thick, slid into the active pit. Post-slide investigative drilling and laboratory testing was incorporated into a FLAC 3D model to determine the conditions at the time of the slide. Unusually high precipitation and the presence of low-strength mudstones were determined to be the cause of the slope failure. Additional drilling and computer modeling has been used to develop a mining plan for the slide block, which is being successfully mined at this time.