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.
Article published in the June 2018 edition of the South African Builder