Numeric model of a cemented rockfill span test at the Turquoise Ridge Mine, Golcanda, Nevada, USA

9th International Symposium on Mining with Backfill
Brad Seymour, Mike Jones, Lewis Martin, Bob Schuler,
Abstract Engineers of the Spokane Research Laboratory (SRL)/NIOSH and Placer Dome, Inc., conducted a rockfill span test at Placer Dome’s Turquoise Ridge Mine near Golconda, Nevada. The purpose of the test was to improve safety and increase productivity by using the techniques of a proposed new bulk mining method instead of drift and fill. This test was conducted in competent waste rock so that the stability of the rockfill could be assessed without applying significant weight from the overlying rockmass. The engineered mine roof was constructed in stages by mining and backfilling six adjacent, parallel drifts. The result was a structure measuring 22.9 m (75 ft) wide, 30.5 m (100 ft) long, and 4.6 m (15 ft) high. Approximately one month after the last drift was filled, the rockfill was undercut by driving two 4.3 m (14 ft) wide by 4.6 m (15 ft) high drifts, which were spaced 5.2 m (17 ft) apart. This left a central pillar that was retreat-mined in sections in order to produce a room measuring 13.7 m (45 ft) wide and 30.5 m (100 ft) long. The researchers visually inspected the rockfill after the undercutting sequence was completed and determined that it remained stable with no detectable roof sag. They confirmed these results by recording vertical borehole extensometer displacements in the mine roof and rockfill. The maximum measured vertical displacement of the rockfill was less than 5 mm (0.2 in). The extensometer data were also used to validate a three-dimensional numeric model of the rockfill. The subsequent results indicated that no failure zones developed in the rockfill; this further confirmed the visual observations. The numeric model was then used to simulate load on the rockfill produced by dislodged material from a weak mine roof. The load was in the shape of a triangular prism with specific weight of the host rock, the base measurements equal to those of the rockfill, and a height of 11.0 m (36 ft). The additional load did not cause failure in the modeled rockfill indicating that it could support more than its own weight.
Keywords: Stability, span, undercut, Rockfill
Full Access to Technical Paper
PDF version for $20.00
Other papers from 9th International Symposium on Mining with Backfill