DSI stabilize the largest Excavation for a Single Project in South Africa: The new Discovery Office Building

Currently, a new office building is being constructed north of Johannesburg, South Africa for the insurance and financial services company Discovery in Sandton. The centrally located 87,000m² office building will offer room for more than 5,000 employees that are currently working in four different buildings.

The 24,435m² excavation represented a major challenge to all parties involved due to its size and to the work that had to be completed within 12 months. First, the existing buildings occupying the site had to be demolished. The last part of the construction site could only be vacated 4 months after commencing the project.

The final excavation volume reached 565,000m³; this includes 180,000m³ of hard rock blasting. Afterwards, gunite had to be applied on a surface of 15,540m². These quantities surpass those of any single super basement in South Africa.

The excavation support design had to accommodate a 33m high vertical face hard-up against the heavily used Rivonia Road. The highly variable and complex ground conditions necessitated constant lateral support, design reviews and meticulous co-ordination between lateral support, earthworks, blasting and demolition contractors. Furthermore, in some places, the constant presence of subterranean water lead to instability so that geotechnical systems were also needed in these areas. A layer of pegmatite was encountered along the south and eastern elevations, necessitating anchor systems with between 60 and 70% higher load-bearing forces.

As a result of the exceptionally high soil faces to be retained, high capacity DSI Strand Anchors with load-bearing capacities in excess of 100t each and exceeding 24m in length were installed along Rivonia Road and along the existing buildings. In addition, steel section walers weighing more than 300kg each were utilized to distribute the additional anchor forces among the soldier pile members.

In total, Rocbolt Technologies supplied anchor systems for stabilizing 15,540m² of excavation walls. For this purpose, 1,311 12-14m long DSI Strand Anchors and 943 25mm Ø DSISoil Nails were used that were installed in layers.