Franki Africa – leading Geotechnical Engineers in South Africa. Part of the Keller group which is the biggest in the world. Franki Africa is the largest, oldest and most established specialist geotechnical contractor in Sub-Saharan Africa. Franki offers a comprehensive range of services which ensures that its customers benefit from the most cost-effective solutions for their geotechnical requirements.
Franki operates in sub-Saharan Africa and the Indian Ocean Islands and, together with Keller, has the experience, capability and capacity to undertake projects of all sizes. The comprehensive product range at Franki is further enhanced by its in-house geotechnical investigation capability, as well as its Design Department. Being part of Keller (www.kellerholding.com) also widens our product range, capacity and capability
[Johannesburg, 7 September 2018]: The old adage that building roads and bridges is fundamental to the growth of an economy has certainly been heeded by the Saldanha IDZ (Industrial Development Zone), which, in contrast to many areas in South Africa, has been undertaking significant infrastructural development with the funds they have received from the South African government for that specific purpose.
Some of this infrastructure includes roads and bridges such as the Greenfields Link Interchange project, awarded to WBHO Construction in late 2017 and who subsequently awarded the geotechnical piling contract to Keller’s Franki Africa.
The project, initiated by the Western Cape Government: Department of Roads and Public Works, is situated in the Saldanha Bay municipal area 125km north of Cape Town.
Franki senior contracts manager, Anton Stoll, explains that at tender stage the pile founding solution was stipulated as “predrilled, based temporary cased auger piles” for all three bridges, founding in the greenish, grey mottled orange and brown dense sand, by means of basing out an enlarged base below the temporary installed casings. These piles were expected to be around 14m in length from underside of pile cap.
“From the outset we were not quite sure that the tender solution was the correct one for the circumstances,” says Stoll. “The fact is the West Coast area around Saldanha Bay is known for its difficult geology and founding conditions for many a structure, including, of course, this particular bridge interchange.
He adds that the geology of the site consists of windblown sands for around 0.5 to 1.0 m below natural ground level, followed by up to 3-4m of strongly cemented hardpan calcrete (pedogenic), then varying layers of loose, silty, clayey sand and calcrete lenses, followed by a greenish, grey mottled orange and brown dense sand. This varying profile continued to depth and a high-water table was present.
The Interchange has three bridge structures and, while the largest structure was clear of any obstructions, the other two had a water main in close proximity to the piles and pile cap, raising a concern over vibration during pile installation further complicating things from a geotechnical perspective.
The ultimate outcome was that Franki decided that the site conditions suited a different pile type and installation methodology with the varying soils, the very high-water pressure and an aquifer which became evident in close proximity to where the piling would be.
“The water had further softened the dense sand layer in places, making the formation of the enlarged base difficult due to large volumes of basing material required to improve the silty sands,” says Stoll. “As more skips were added, the basing appeared to soften rather than densify the layer. At times, plumbs were added without effect ultimately resulting in the plug suddenly being expelled by the 6-ton hammer from the temporary casings allowing water into the casing. After a number of attempts, it was proposed that an alternative piling solution would be more suitable to the site conditions, geology and pipeline obstructions.”
After discussion with the engineers and main contractor, Franki proposed that the two bridges with the existing water pipeline obstruction would be more suitable to CFA (Continuous flight auger) piles while the main bridge could be found on DCIS (driven cast-in-situ) Franki piles founded at a dense layer, higher up in the soil profile. This required a variety of piling rigs, service cranes and technical skills, all available within the Franki group.
Stoll says that by this time, the programme had become critical and the merits of the alternatives were debated, approved and immediately implemented with non-working test piles at each structure. Predrilling remained in order to penetrate the hardpan calcrete layer prior to installing the piles.
The test pile results proved the alternative methodology was correct and working piles were installed accordingly.
Franki has developed a reputation far and wide for finding the right solution for the job at hand. “Our experience in South Africa and in many parts of Africa in general over the years gives us an unmatched understanding of the geology and of what is required relative to it to ensure that we give our clients the most cost-effective solution,” Stoll says. “The Green fields Link Interchange is certainly not the first time that we have successfully offered a solution different from that of the tender proposal.”
Of course, knowledge is one thing but having the right hardware for the job is as important. In this case the CFA piles and the world-renowned Franki Pile, which has been used extensively throughout southern Africa for the past 70 years (and is still today one of the most popular pile-types) proved their worth in the solution.
The main feature of the Franki Pile is the enlarged base formed at the toe of the pile. In forming this base, the end-bearing area is increased significantly and the displacement achieved when expelling the plug and forming the enlarged base compacts and preloads the soil surrounding the base. Thus, the end-bearing of a Franki Pile in sands develops at much lower base deflections than that of a bored pile.
Other important advantages of the Frank Pile include: it is often a very economical system; it has an extensive range of pile sizes; it has an exceptional load/deflection performance; noise levels are relatively low; it has excellent tension load capacity.
The CFA piling system is also a fast and economical one, which has no vibration and limited noise levels. Some of its other attributes include: high production levels in suitable soil conditions; economical in suitable soil profiles.
“The fact is there are some limiting considerations to be taken into account with the CFA system reducing its popularity compared with driven piles. The conditions in the Greenfields Link Interchange, however, made the system a very successful choice,” Stoll says.
The key to the success of the piling project was the implementation of Franki’s alternative plan. “It took teamwork to get this right,” says Stoll, “and I would like to pay special tribute to Ross Dold, Nabeel Omar and Wilhelm Wessels on site for Aecom, together with Abie Newmark and Alexi Maraveilas from the Aecom office, while Stefan Herbst and Willie Broekman of WBHO Construction assisted us with the implementation. This was indeed a great team effort,” he says.
Stoll emphasised that no project is too big, or too small, or too complex for Franki. In terms of South Africa and Africa in general we are geared up like no other geotechnical company in the world. We have permanent offices and yards in South Africa, Mauritius, Mozambique, Tanzania, Zambia, Kenya, Ghana and Angola. We are also registered in Uganda, Botswana, Swaziland, Lesotho, Seychelles and Namibia. Our French speaking colleagues are present in Morocco, Cote d’Ivoire and Algeria and our middle eastern colleagues are present in Egypt.
“Add to this the depth of global experience that the Keller group has it becomes clear that Franki’s ability to provide a world class service in this country and across the continent is second to none,” he concluded.
Frank Africa contact details:
031 507 1051
MoonDawn Media & Communications
For construction programmes to be compressed into the shortest possible time to meet client handover deadlines is not unusual, but for contractors to offer innovative improvements to design to realise cost and time savings is far more so – particularly when this increases the pressure on the contractor to perform! For the prestigious new Umhlanga Arch development, north of Durban, KZN, the Keller group’s Franki Africa, through innovative solutions and unusual industriousness, did just this.
Umhlanga Arch is a 45,000m² residential, commercial and hotel development situated on prime Umhlanga Ridge real estate with expansive views over the Indian Ocean. The demand for space in the suburb has been insatiable and development has been continuous even in the current tough economic conditions. Typically, an urgent start and fast track programme to ensure handover to new tenants as early as possible was demanded.
Innovation for Time and Cost Saving
When Franki’s team reviewed the tender requirements, it was clear that the earthworks and piling could not be completed within the time frames specified. Early access was required to the main structural cores of the high-rise buildings but this was inhibited by their close proximity to deep cuts into the steeply sloping site.
Graded embankments for staged piling platforms would only allow access to key core piling platforms late in the piling programme so Franki proposed additional anchored lateral support walls as an alternative and, in conjunction with the client and the project team, these were worked into the foundation design to realise overall time and cost savings.
But Franki offered many other innovative time and cost saving solutions to the earthworks, foundation and lateral support requirements which were integrated into the structural design while work continued. This included ingenious geotechnical optimisation, which resulted in the approximately 1,300 foundation piles being halved with the introduction of large diameter (750mm and 900mm) Zwidi DCIS piles.
Programme constraints were further alleviated by Franki introducing additional contiguous piled lateral support enabling earlier commencement of the foundation piling and subsequent main structure. This resulted in Franki’s lateral support scope increasing to approximately 3,000m² of anchored pile lateral support which, along with the foundation piles and earthworks, was all to be completed in less than 6 months.
Furthermore, careful coordination with the client, local authorities, other contractors and the project team resulted in bulk earthworks and piling starting simultaneously allowing the early introduction of the building contractor in yet another solution to bring the completion date forward. In addition, further temporary lateral support solutions were found to allow early access to other key areas.
The Construction Techniques
The lateral support works comprised retained heights up 9m with nearly 320 anchors up to 19m long in two to four rows. These had to support construction traffic as well as adjacent roadway traffic. The Berea Red sands are fairly consistent in this area, but CFA piles and self-drilling hollow bar anchors were used to accommodate bands of loose collapsible sands.
The added complication of installing piles behind anchored lateral support required the accurate positioning of anchors to avoid pile positions. Although there were certain conflicts, these were overcome without any major design implications.
Foundation piling began away from the deepest cuts, but access had to be provided for foundation piling to the critical cores of the main structure – some of which were close to deep cuts – in the shortest possible time. The Zwidi pile proposed by Franki is a derivative of the Franki pile and is suited to unsaturated soils, which do not collapse, found in some areas of Umhlanga Ridge. They are large diameter piles with enlarged bases and can carry high loads. One of their main advantages is that they can be installed relatively quickly.
Building works commenced on site as soon as the first section was handed over and from then on, the main contractor for the building works applied continuous pressure on the Franki team which did not flinch and was able to provide safe access to meet the stringent deadlines. With access from one steeply sloped point only, the potential for conflict between disciplines was ever-present and required continual liaison between all concerned.
Heavy run-off from adjacent roadways and the site itself had to be carefully managed, as sites further down Umhlanga Ridge could not accommodate concentrated flows. With the works largely taking place during Durban’s wet season, rainfall and flooding were responsible for frequent work stoppages when the site was flooded but major erosion and downstream flood damage were prevented.
The lateral support and piling works could not have been completed in the specified time frame without the value engineering offered by Franki. “Although the products offered were not, in themselves, necessarily new or innovative, they were part of innovative and inventive engineering solutions which met the demanding requirements and ensured that this project could meet the client’s expectations in terms of safety, time, cost and technical competence,” says Franki’s Paul Pearce.
He added that the success of the project depended to a large extent on the co-operation of all involved. “The client was open to suggestions and by allowing adequate time for tender, design review and incorporation of changes, the right solution was found to the benefit of all. The on-site management of the different disciplines was also critical and without the buy-in of the piling, earthworks and building contractor, the timely sequencing and completion of critical sections could not have been achieved,” he concluded.
All critical piling handover dates were met with non-critical elements being completed in line with the provision of access and without any delay to the overall programme.
MoonDawn Media & Communications
Frank Africa contact details:
031 507 1051