Mine, Community and Agencies Rely on Numerical Modeling to Assess Sensitivity of Highwall Movement

ABSTRACT: Expansion of the Homestake Mining Companie's (HMC) Open pit in Lead South Dakota required the relocation of a state highway, several businesses and a number of residents. Historically, some areas surrounding the open pit have exhibited movement because of fluctuating groundwater levels, historic surface and underground mining and the variability of geologic strata. Expansion of the open pit toward the south encroached well into the City Limits of Lead South Dakota. The design called for excavation of the open cut down 800 ft at an overall slope angle of 48° adjacent to town. HMC worked with town officials designing the expansion to include a Visitors Center, Gift Shop and a new Town Park adjacent to the pit on the south rim. The expansion was designed to recover a significant amount of reserves that were down plunge from the main structure in an area that was previously mined using a variety of underground mining methods, Therefore, the bottom 350-ft of the 800-ft highwalls was expected to be founded in remnant stope backfill and caved rock.