Characterization of a large slope failure in an open-pit mine through the back-analysis of satellite InSAR and ground- based radar data

The object of this paper is the investigation of a large slope failure that occurred unexpectedly in an undisclosed copper open-pit mine. The nature of the event urged for a thorough back-analysis of slope monitoring data in order to characterize its actual size and temporal evolution, and to identify whether precursors potentially able to anticipate the incipient failure were present. To this aim, satellite InSAR measurements relatively to the period of interest were, in retrospect, acquired and coupled to those derived by a ground-based radar that was in use in the pit at the time of the failure. Rainfall records, pre- and post-event topography, and a field mapping of the failure complemented the review of the slope displacements. Although a small area affected by accelerating creep could have been identified in correspondence of two benches in the uppermost part of the pit, the satellite InSAR dataset revealed that the vast majority of the instability actually involved a slope sector above the mine crest and was therefore not visible by the ground-based radar. Following the high revisiting time of modern satellites (up to 6 days for the Sentinel satellites used in this study), a clear accelerating creep behavior beginning one month before the event was observed for the first time in spaceborne interferometric radar data over an open-pit mine. The delimitation of the area where satellite InSAR measurement points featured accelerating creep matched the margins of the failure as mapped in the field. By comparing displacements with rainfall records, it was also observed that the initiation of the failure process was most likely related to an intense precipitation season. The results provided crucial advancements concerning the joint use of ground-based and satellite slope monitoring data, demonstrating the complementarity between the two techniques and the value of their combined use to reduce the uncertainties associated with the management of slope failure risk.