Extending the Service Life of Wessels Vent Shaft, in Hotazel, South Africa: Fid-Bau Portal

Extending the Service Life of Wessels Vent Shaft, in Hotazel, South Africa

Strydom, Johnnie / da Silva, Jared / Manganye, Tshepo

This paper presents the extension of life for the vent shaft at the Wessels Manganese mine in Hotazel, Northern Cape, South Africa. The existing vent shaft comprises a concrete box-type structure sloped at 6% to allow vehicle access to the underground operation in emergencies. In addition, the vent shaft supplies vital air to the mine, thus closing of the shaft is not possible. The new rail balloon intersects the shaft perpendicularly, on a fill of 10 m. The existing vent shaft was constructed using low-strength concrete with mild steel reinforcement bars that were available at the time of construction and therefore does not have the required structural integrity to carry the fill and associated rail loading. Several options were evaluated to extend the service life of the vent shaft, including building a bridge over the shaft and constructing a new vent shaft that would daylight at a different location. The most feasible solution was to keep as much as possible of the existing vent shaft and construct new sections under the high-fill regions. Rapid impact compaction was required on the collapsible in-situ soil conditions. To ensure uninterrupted air supply, a collar was introduced over a section of the existing shaft, equipped with a chimney to serve as temporary air vents. This allowed for the upper portion of the shaft to be demolished and rebuilt, thereby extending the structure’s service life. Additionally, wing walls were constructed at both the top and bottom to prevent the new rail fill from encroaching on the remaining portions of the old vent shaft.