Construction World December 2023

TREVENNA SUPER BASEMENT PROJECT C oncor was appointed by the Public Investment conducted. Concor is committed to limiting the environmental impact of its projects,

AfriSam Innovation Award for Sustainable Construction

Corporation (PIC) as the principal contractor on the large and challenging Trevenna Super Basement Project in Sunnyside, Pretoria – which has created a ‘future proofed’ five-level basement as a precursor for A-grade office buildings in the Trevenna Office Campus. To prepare the way for the future evolution of the upper structures, the scope of work also included extensive underground services such as sewer and stormwater infrastructure, electrical reticulation, lifts to the ground floor and access control. Covering almost 70 000 square metres of parking space and other amenities, the super basement extends 20 metres below ground level. This meant that the basement floor was 12 metres below the water table, creating significant groundwater and rainwater challenges. Hard rock conditions were also encountered and required controlled blasting and other excavation to reach the required levels. The Trevenna Super Basement is in a busy urban area, surrounded by high density residential accommodation. Community engagement was therefore key to the project’s success, as was careful planning, effective communication and a flexible approach from the contractors. To facilitate the fast pace of construction, Concor deployed five tower cranes on the site for expediting movement of steelwork, formwork and other construction materials. Space was at a premium due to the busy urban location, and the footprint of the basement extended across almost the entire site. In preparing the ground for the basement, Concor was required to work in rock with a hardness up to 250 MPa, and 12 metres below the natural water table. Controlled blasting was applied, and sumps and channels created to pump water continuously from the site. Careful planning and hands-on implementation of resources allowed Concor to break up the challenging areas into manageable blocks – to progressively work towards the upper levels. During construction, a key innovation was the use of post-tensioned beams throughout the super basement. This allowed for thinner slabs and reduced the concrete and rebar requirement - adding to the overall project’s green star strategy. The post-tensioned designs provided flexibility for the design engineers in terms of loading and constructability within the large super basement structure. Dealing with water ingress required

including the reduction of the carbon footprint through lower emissions. At Trevenna Super Basement this was achieved in various ways. The local participation of subcontractors and suppliers meant that most resources – in labour and materials – were from the Tshwane region. The various concrete mixes for the columns, walls and slabs, supplied by readymix specialist AfriSam, were specified to have a 30% replacement of cement with fly ash to reduce its carbon footprint. This provided a green star mix of four stars in terms of the Green Building Council of South Africa criteria.

The main supply for the readymix concrete also came from AfriSam’s nearby Ferro Plant in Pretoria North – just 14 km from the site – ensuring carbon emissions from the readymix trucks were minimised. AfriSam also supported the project’s environmental sustainability aims by managing the production and delivery of readymix in a responsible manner that reduced waste. Management of water on the site was done in compliance with the client’s water use licence. Working below the water table meant continuous pumping of water from the site, which required the measurement of water volumes leaving the site and entering the city’s stormwater system. The future-proofing of the super basement meant that all foundations and vertical structures were designed to accommodate the top structures – which at the time of the basement’s construction were not yet designed. 

PROJECT INFORMATION

• Company entering: Concor Construction • Client: Public Investment Corporation • Main Contractor: Concor Construction • Architect: Paragon • Principal Agent: Origin PM • Project Manager: Origin PM • Quantity Surveyor: Crane QS • Consulting Engineer: NAKO ILISO

extensive waterproofing of the structure, so hybrid systems were used to ensure no ingress of rain or underground water. This included the use of concrete additives in shaft pits and waterproofing applications slab levels had to tie up with existing adjacent basements, requiring ramps to be designed and constructed. Where access portals were necessary, these were supported with structural steel while concrete cutting or stitch coring was on tanks to ensure no leakage. The Trevenna Super Basement

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22 nd Best Projects Awards 2023