Geotechnical contractor Franki Africa, part of Keller Group, is using its own in-house design and expertise to provide the geotechnical solution for Phase 2 of the V&A Silo District basement for V&A Waterfront Holdings, represented by Mace Project Managers.

The contract started in January and is scheduled to be completed in March 2015 at current progress.

The scope of work involves the lateral support for the new basement, foundation piles for the structures and lift shaft anchors for the grain silo development.

Franki Africa senior contracts manager Anton Stoll says Franki had to deliver a variety of products and services, while dealing with tidal conditions, varying rock profiles and restricted access within a public place. “This has definitely been one of our most challenging contracts.”

Zeitz Museum of Contemporary Art Africa (MOCAA), a new not-for-profit institution, will be housed in the historic Grain Silo, with the V&A committing over R500-million to the development required for the establishment of the museum. The museum is the result of a partnership between the V&A Waterfront and German businessman and art collector Jochen Zeitz, who is donating his collection of African art to the museum on a permanent basis.

One of the most demanding aspects of the contract was the varying geological profile of the site, combined with strong underground water movement caused by tidal changes.

Stoll notes the geology consists of imported fine silt and clay sands and rock fill overlying highly fractured greywacke residual rock, which improves with depth. There are also old beach zones with sand and shelly fragments in areas overlying the residual rock. “The residual bedrock can vary up to 13 m over the site, making this a challenging piling environment particularly when we need to ensure we have minimum socket lengths for tension loads in some piles.”

However, he says that “by far” the most difficult aspect of this job is the site itself. “The V&A Waterfront is not only a live, working environment, it is also one of the most visited destinations in the country, attracting huge volumes of public foot- and vehicular-traffic.”

Stoll says the main challenge is to disrupt the normal flow of activity as little as possible, while performing the necessary tasks, which include, among other things, rerouting many old and unknown services and negotiating Franki Africa’s large equipment and machinery around the site, while trying to achieve production targets. “Under such circumstances, planning is never easy, especially when services cannot be located prior to piling, and there have been numerous delays as a result, making progress difficult.”

These challenges are overcome by manipulating the numerous resources on site and by trying to finish in areas that are accessible, while preparing to work in other areas.

“The excellent working relationship between main contractor engineering and construction group WBHO, Mace and Sutherland Consulting Engineers and Franki Africa has resulted in a joint effort that will ensure that time and production targets are met despite the fact that, so far this winter, the Cape of Storms has lived up to its name with rain making the concrete sheet piling operation challenging.”

Diverse Products Required
From a practical perspective, this contract requires a wide range of geotechnical product solutions.

Driven concrete sheet piles with grout socks and anchors are required to form lateral support on the north and east sides of the basement. These consisted of 228 piles of 206 m long, ranging in depth from 9 m to 13 m. The grout socks were used in between the concrete sheets for waterproofing.

Forming lateral support on the south side of the basement, were 148 permanently-cased odex piles of 325 mm diameter with arched gunite, waler beams and anchors.

In addition, 299 temporary-cased augered piles of 750 mm diameter were used, which were permanently lined for foundation piles.

Further, 356 Franki cast-on-site, permanently lined foundation piles of 610 mm diameter were also required.

Lateral support was provided with 184 anchors anchoring systems.

The silo lift shaft required 32 tension anchors of 1 000 kN.
Franki also provided geotechnical investigation works with limited headroom within the silo building, consisting of 11 core-drilled holes.