Phoenecian completes work on ‘super basement’
By Leila Steed20 July 2022
South African contractor Phoenecian Group has used its expertise in demolition to complete the bulk earthworks for a five-level ‘super basement’, as part of a new office development.
The Trevenna office complex, which is being built just outside of Johannesburg in the city of Pretoria, Tshwane municipality, features a five-level basement that extends for 20 m (65 ft) below the surface.
The design of the structure, which is made from post-tensioned concrete slabs, incorporates extensive underground sewer and stormwater infrastructure, electrical reticulation, lifts to the ground floor, and access control.
To carry out the works Phoenecian used two 30 t excavators to remove 193,000 cu m (6.8 million sq ft) of soil and rock from the 38,600 sq m (415,000 sq ft) site, as well as drilling and blasting to remove a further 80,000 cu m (2.8 million cu ft) of material.
A fleet of 10 cube trucks was used to transport the excavated material to a nearby military base, where it was used to build up the berms (walls of earth) at the base’s shooting range.
Grant Luck, contract manager for Phoenecian’s demolition and earthworks division, said: “It highlights our capability to undertake the largest super basement projects in South Africa. Building on our expertise as a demolition company, we have the flexibility to undertake any earthworks or lateral support requirements.”
According to the company, the site presented a number of challenges, including the relocation of an existing stormwater drainage pipe and the type of rock formations embedded in the ground.
“We had a lot of overbreak that required engineering input as to the designability of the rock face,” said Grant.
Phoenecian also completed lateral support works for the structure, drilling holes at a predetermined depth for the installation of anchors. The anchors supported a mesh wall sprayed with layers of gunite - a mixture of cement, sand, and water applied by a high-pressure hose.
“The guniting could not exceed 100 mm (4 in) a day, with the thin layers applied to the mesh wall ultimately hardening into a concrete wall providing the necessary lateral support for the super basement,” said the company.