The implementation of a monitoring system able to catch geotechnical events in large-scale open pits is challenging and requires a combination of different technologies, since rock masses are heterogeneous. Traditional monitoring systems commonly treat rock masses as a discrete and homogeneous domain, which is not representative of the global slope failure process with differentiated deformation along the structure, due to different rock types, joint families and rheology. Interferometric radars have been used as a potential tool in monitoring large-scale geotechnical failures, since they could give a rapid response in all scale deformation, characterize the behavior of the movement, and predict failure time using tools, as inverse velocity. Regardless of the scale of slope monitored, the data obtained is rarely associated with rock types and rheology. This article presents an optimization of a large-scale slope monitoring system, correlating interferometric radar and geological compartmentalization, in a real case of global slope failure.
The Gongo Soco Pit is located in Barão de Cocais, Minas Gerais, Brazil. Mining activities started in the late 18th century, with the exploration of gold, and continued until the beginning of the 20th century. Around 1989, iron ore production started in Gongo Soco and continued until 2015, when all operation ceased.
The Gongo Soco pit has two main slopes, North and South Wall (Figure 1). Each one has its own geomechanical characteristics. In addition, the absence of a water pumping system after mining closure increased superficial and groundwater levels, resulting in a lake on the bottom of the pit. Since 2002, the North Wall has been presenting deformations. However, in a global point of view, the slope presented low deformation rates for radar and prism data. In 2019, a major mechanism of a structurally controlled planar failure (called Primary Failure) started at the central portion of the north slope and a robust monitoring system was implemented. In January 2020, the deformation rate reached its maximum value (the peak) and the slope started to gradually fall. The Primary Failure initiated a residual deformation stage after this event. Besides that, as a consequence of the Primary Failure rupture and a heavy rainfall season, a second failure in the northeastern portion of the Gongo Soco pit (called Secondary Instability) started a deformation process, with high deformation rates and velocity. Since then, the North Wall has been the subject of different studies and analysis, encompassing all aspects related to the rock mass as, for example, the geological properties. The present study is focused on the North Wall global ruptures and the monitoring system designed to optimize the analysis of movement and deformation, considering the correlation between interferometric radar data and the geological compartmentalization.
