Monitoring of a Rock Slope Using Crack Displacement Measurements in an Observation Drift at the Une Mine

Abstract

Mt. Buko's rock slope has been formed by mining activity since 1973 and it will be 800 m high and 5 km long at the end of the mining operations. To manage the rock slope in a stable condition over the long term, mining companies operating at Mt. Buko have conducted numerical analysis of the rock mass and installation of various monitoring devices, such as APS (Automated Polar System) and GPS (Global Positioning System), on the slope surface. APS measurements have shown a sudden and obvious displacement of a section of the rock slope of Une Mine that likely occurred during heavy rainfall in September 2007. This was a different behavior pattern from the expected elastic deformation. It was clarified that displacement measurements in the rock slope, in addition to slope surface measurements, were important for understanding the overall behavior of the rock mass and for determining effective countermeasures for the displacement. In 2008, an observation drift was excavated in the center of the displacement. Measurements of the rock mass were taken along a 307m long observation drift using several crack gages and a total station. Analysis of the long-term monitoring data in the drift has shown that the displacement inside the rock mass corresponded to the data obtained by APS and GPS. Moreover, measurements in the drift were much more stable (showing high accuracy and reliability) than those on the surface, which tended to be affected by meteorological conditions such as lightning, heavy rain and dense fog.

Keywords

• observation drift
• crack gage
• rock slope monitoring in rock mass