Soil Nails Stabilize a Huge Open Pit Mine

Context

The mine is located in southeastern Brazil, only 10km to the northeast of Belo Horizonte. Until the depletion of the iron ore reserves in 2002, approximately 300 million tons of iron ore were extracted from Águas Claras over an area of roughly 1,000ha. After the mine was closed, the deep pit was partly filled with water, which created a large lake over the years.

Before the mine was closed, a large landslide occurred in 1992, causing a part of the Curral Ridge to collapse. A 2008 report also detected many steep slopes that were not covered by vegetation and therefore exposed to erosion. However, the shutdown and rehabilitation of the mine area, which had been planned for the years 2003 to 2013, were repeatedly delayed.

Since the former mine is located in the immediate vicinity of a densely populated area, the uncovered, steep slopes in the open pit mine represented a major security risk. In 2013, the owner Vale decided to carry out stabilization measures in order to minimize the risk of landslides and to enable the future use of the entire area.

Solution

Within the scope of the project “Cava Oeste”, the comprehensive stabilization of the highest portion of the western pit started in August 2014. During this project, loose soil was removed and a drainage system was installed that will prevent future erosion. Afterwards, a stepwise slope stabilization is carried out from the top down. The slopes are stabilized using high-strength steel mesh and revegetated following installation.

The passive steel mesh slope stabilization system is anchored in the stable slope strata using DYWIDAG GEWI Soil Nails that act directly on the slope surface. 47,535m of 32mm Ø, GR 50/55  DYWIDAG GEWI Soil Nails with a weight of 21t were installed to safely secure the steel mesh. DYWIDAG supplied the soil nails complete with 7,310 nuts.