Development of an early-warning time-of-failure analysis methodology for open-pit mine slopes utilizing ground-based slope stability radar monitoring data

Abstract

The recent introduction of ground-based slope stability radar in open-pit mines to complement conventional geodetic monitoring programs provides near real-time deformation measurements over a broad coverage area; this allows geotechnical engineers to observe the spatial distribution of pit wall movements and their progression over time. This paper presents a newly proposed early warning time-of-failure (TOF) analysis procedure for use in real-time with ground-based radar measurements designed to be integrated in an open-pit mine’s trigger action response plan (TARP). The inverse-velocity and slope gradient (SLO) TOF analysis methods are applied to radar displacement measurements using a new systematic multi-pixel selection technique termed the “percent deformation method.” The utilization of the percent deformation method in the proposed real-time TOF analysis methodology gives more-reliable results than current practice by providing recommendations for pixel selections, data filtering, where and how to undertake TOF analyses, and presenting TOF results in real time. The addition of a more rigorous, methodical treatment of radar monitoring data when faced with critical slope instability will reduce uncertainty and increase confidence in any trigger action response decisions, helping to ensure a safer work environment.

Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses

“…and the smoothing factor is β = 0.5 If the time interval between adjacent measurements is constant, the type of moving average as in (2) is equivalent to the simple equation utilized by Dick et al (2014) …”

“…Graphs have been divided in two sections, before and after an identified OOA/TU point. As previously said, this marks either the point after which a trend toward the x-axis can be clearly defined or a change in the trend slope and usually occurs together with a reduction in data noise (Dick et al 2014).…”

“…3a. Life expectancy plots are very useful tools to examine the course with time of the T f predictions, updated on an on-going basis each time a new measurement is available (Mufundirwa et al 2010;Dick et al 2014).…”

“…Rose and Hungr (2007) also assessed that the inverse velocity plot often approaches linearity, especially during the final stages of failure; they also highlighted the need to seek consistent linear trends in the data and their changes. On this subject, Dick et al (2014) suggested that the linear fitting procedure should only include data following the identification of Onset Of Acceleration (OOA) points; they also advised that additional fitting should be performed if a TU point (Trend Update, i.e. significant change in the acceleration trend) is detected.…”

“…Dick et al (2014) carried out a sensitivity analysis for an open pit mine slope failure case history, which showed that variation of T f for rates filtered over a short time period produced larger variations compared to rates filtered over a longer time period; however, the topic was not comprehensively examined as in the terms proposed here, and the main focus was directed towards the correct handling of spatially distributed ground-based radar data in monitoring open pit mine slopes. It should also be noted that different filters may generate different results depending on the shape of the rate acceleration curve and on the level of noise intensity.…”