In the late 90s, the excavation of an open pit mine was initiated in the Iron Quadrangle, a rich iron ore region situated in southeast Brazil. During years of excavation and mining duties, but especially after reaching its maximum depth, many instabilities occurred in the north wall, which presents about 500 m height and overall slope inclination that fluctuates between 30° to 35°. In the 2010s, a Real Aperture Radar and a series of prisms distributed across this wall indicated a total displacement of about 65 cm in 120 days during severe rainstorms. More recently, in the 2020s, InSAR data have shown that the displacements are still occurring after many slope failures, especially during the rainy season. As a result, the extensive erosion process accelerated the wall unloading generating a net of several unstable surfaces (comprising millions of cubic meters) controlled by the regional structural setting. Thus, during the design review of the remediation project, according to the reduced data available, several analyses were conducted to confirm the geotechnical parameters obtained from field and lab tests and assess the failure depth from back analyses. Finally, the design review service shows that the remediation proposed by the basic design could no longer address effective treatments for the decommissioning design of the north wall, but the remediation actions are still valid.
The mine is localised in the northeast of a region known as Quadrilátero Ferrífero, a mineral-rich zone situated in the southeast of Brazil where the rainy season is well established over four months with cumulative precipitation over two thousand millimetres. The first reports of mineral exploration in the mine date back to the 18th century (around 1745) as a gold panning using enslaved labour. In the 19th century, gold production dramatically reduced to just a few grams, paralysing the mine for several decades. However, in the late 20th century, a mining company expanded a narrow ancient gold mine into a world-class iron ore open pit. It operated until 2015, when the mine was declared closed and a legacy mine, about 350 Mt of iron ore had been extracted from the mine in this period.
