A new analysis demonstrates how the use of bolts, mesh and shotcrete influence the safety factor for ground support programs
Pursuing gold that cannot be seen with the naked eye in progressively weaker rock at its Turquoise Ridge mine in Nevada compelled Barrick to reconsider its drift support plans. Dissatisfied with the research available on the topic of shotcrete support, Senior Geotech Engineer Louis Sandbak and his team gathered the data from various tests conducted there and released an erudite white paper packed with numbers. It provided the proof needed to justify some costs and formalized some common understandings. Sandbak said historically miners normally erred on the side of caution and acted on industry standards that typically weren’t easily sourced. What everyone knew, he said, was backed statistically when testing in the gold mine revealed shotcrete used in conjunction with bolts and mesh in some cases doubled the local safety factor.1 Now available online, the paper can be referenced by miners seeking to ensure safety when working in medium and weak rock. Some of the conclusions, he said, could change the way shotcrete is used.
The example drift is 14 ft (4.3 meters [m]) wide. The report described it as “situated in ore of the Type IV and Type III weak rock class categories that necessitate the use of bolts, mesh and 2 in. to 4 in. of shotcrete.” Sandbak described it as very weak. “We could have ground that we have standup times of almost immediate collapse to hours or days,” he said. “If it didn’t have any support it would just collapse or cave.”
