At the West Elk Mine (an underground coal-mining operation on the western slope of the Colorado Rockies), the first indication of unstable slope conditions occurred during construction of the mine portals in 1980, and was thought to be localized and shallow. In early 1997, the landslide moved more than a foot in three months. Calculations showed that it was accelerating, threatening the mine facilities downhill. The Mountain Coal Company initiated an emergency action plan and asked Barr to investigate the landslide and design mitigation measures.
Barr’s team characterized the extent of the slide and the depth of the slide failure plane, as well as the area’s soil and groundwater, and determined that the slide was massive. We confirmed that groundwater was a key factor, so extensive dewatering measures were designed and constructed to provide long-term stability.
To reduce the immediate momentum of the slide, we designed a network of flexible steel pins. Typically, rigid pins anchored in bedrock would be used to stabilize a landslide, but these would be sheared off by the mass of this slide. Barr’s design uses pins made of steel pipe, which flex to prevent them from breaking while still resisting the landslide forces. Rather than being embedded in bedrock, the pins tie the faster-moving upper soil layer to the slower-moving layer below to provide a braking force. We continue to monitor and evaluate the landslide and have contingency plans ready if it reactivates.