SRK undertook a review of pit slope performance and updates of the pit slope designs at three gold mines in the Middle East.
Due to the COVID-19 pandemic of 2020, a planned site visit to gather geotechnical data was cancelled, resulting in a change in approach from traditional geotechnical data collection. The Client’s on-site team collected data from the MapTek iSite laser scanners which we then processed and analysed using Maptek’s PointStudio programme. These data served two primary purposes: (1) review of slope performance of the current pits; and (2) slope stability assessment and subsequent update of slope design.
We ran PointStudio’s Inter-Ramp Compliance module to generate heat maps displaying the variation in bench face angle and berm width across multiple sections of each pit. The data generated were then processed by SRK to produce histograms of inter-ramp angle variability, as well as bench face angle and berm width, enabling excellent visual interpretations of the condition of each pit and compliance with the approved slope design. The outputs from this exercise were not only extremely informative for the mine production team, helping them to understand slope performance, but were also used to inform design recommendation changes in later slope stability assessments.
To assess slope stability, we again used PointStudio to generate a large dataset of discontinuities from the high-resolution laser scans. This involved hand-picking thousands of exposed discontinuity surfaces from all three pits to generate data on discontinuity orientation, area, length and spacing. The use of laser scans enabled data to be generated from all benches of each pit, which is often not possible with traditional on-site pit wall mapping as bench face access can be restricted or unsafe. The discontinuity datasets generated were then used in slope stability analysis which primarily involved S-Block, a probabilistic program that calculates the berm widths required to retain a given percentage of expected failure volumes from slope benches. We were able to accurately calibrate the bench failures simulated in S-Block with observed bench failures visible in the laser scans of the pit walls. This enabled determination of appropriate slope inter-ramp angles required to retain a minimum average of 80% of expected failed material in each bench. As a result, new geotechnical domains were created with updated slope design angles based on structural variability, enabling slope angles to be optimised for several domains across the three open pit mines.
