ABSTRACT
ABSTRACT: On February 5th, 2005, approximately 9.1 Megatonnes of the Gold Quarry North Waste Rock Facility (NWRF) collapsed. The slide covered over 460 meters of Nevada State Route 766 and came within 10 meters of a nearby creek. The slope had been at or near its final design configuration since the early 1990’s (3H:1V). Following an extensive geotechnical investigation, it was determined that the NWRF slide resulted due to strain-softening, fine grained plastic clayey silt that composed the lower 2/3 of the height that failed along the contact with the native ground surface. Instability developed as the clayey silt passed from its peak to residual strength. Stabilization measures to achieve a 5.1H:1V design slope have included unweighting of approximately 11 Megatonnes and constructing a 1.4 Megatonnes buttress. Movement recognized during remediation required design modifications based on current assumptions that the strength properties of the slide surface are two standard deviations less than the average residual strength determined from laboratory tests.
