Piled Foundations
Basements’ Best Shot
Due for completion in 2019, the 96 Illovo development is well underway, with an innovative treatment for its three-storey-deep basement’s retaining walls. ocated on the corner of Oxford and Chaplin roads in Illovo, is a huge hole in the ground, dropping 13 metres to what is destined to be the floor of the fourth parking basement of an office block. The construction site is for the 96 Illovo office development, commissioned by client Victhyme Investments. Dev Devan, project manager at 3D Projects, describes what the development comprises: “The project involves the development of a 7 500 square metre A-grade office block, consisting of four levels of basement and ground, plus three levels of offices. The size of the plot is 3 500 square metres in an extremely tight site.” The site, like all the other new developments underway in the built-up area, is struggling with a confined working space. “One of the challenges in managing this job is the logistics created by having a site that is bound by Oxford and Chaplin roads, as well as the close proximity of a built-up property next door,” Devan explains. Presently underway, but nearing an end, are the bulk earthworks, which are being completed by Harrogate Civil Construction. Pregan Moonsamy, contracts manager at Harrogate, describes the scope of work: “To get to the depth we have, which is 13 metres from ground level, we excavated about 40 000 cubic metres of earth, in about two-and-a-half months,” he explains. Looking around the site, in overcast weather, there are large puddles of water, evidence of the recent storms that battered Gauteng. Moonsamy assures, however, that this has not delayed the project to any degree: “Other than a minor delay around an issue over an existing stormwater pipe, the earthworks are on schedule because the underfoot conditions are good for excavation, as the earth is soft to about seven metres in depth,” he adds.
The good soil that comes from the excavations will be used on other projects, while the rest will be disposed of in municipal dumps. Devan continues: “Presently, we have completed the bulk excavation, by and large, with one section remaining. How we sequenced the earthworks was by starting from the northern face, working towards the southern face, creating the excavation platforms that we required for the piling to get underway.”
The piling operations had literally started on the day of the site visit, with the first pile in progress. Dan Alford, contracts manager at Mega Pile Inland, says that Mega Pile Inland is responsible for the major lateral support works and piling works within the four parking basements. His response to comment on the large puddles of water possibly being from groundwater seepage is: “The significant water on the site was not from water seepage, but from the substantial rain experienced over the past week,”
Alford assures and adds: “We have had about 0.5 metres of rain since the start of the project. Despite this, we are still on track with meeting the deadline, although the rain causes logistical problems with trucks moving in and out of the site. We were concerned about encountering groundwater at the base of our excavation, but fortunately, we have not found any.” When asked about the number of piles, he says with a grin: “96 piles in total. I think this was intentional, as this is 96 Illovo.” The piles are various diameters, ranging from 500mm to 1.2 metres — BIG piles, with heavy steel, to support massive loads. The concrete used in the piles amounts to about 700 cubic metres, with about 40 tons of rebar.
The 13-metre-high basement’s retaining walls are made of wet Shotcrete, Alford explains: “Previously, dry Shotcrete was used. This new wet Shotcrete is an innovation; it reduces wastage massively and also produces a more consistent mix and wall finish. “In the old conventional system, using dry Shotcrete (gunite), the process was to add the water at the nozzle, whereas wet Shotcrete is already mixed. By adding water at the nozzle, the emerging concrete spray can be inconsistent, dependent on the consistency/pressure of the water spray. Now we use ready-mix, which goes straight through the nozzle. This gives uniform quality and moisture consistency, which also reduce wastage considerably. Air entrainment in the mix ensures that when the mix leaves the nozzle and impacts with the wall, it stiffens, or firms within about 20 minutes,” he adds. Alford says that initially, the mix contained stone, measuring 9–14mm, but that changed. “While the finish was okay, we removed the stone and increased the sand content, resulting in a much nicer finish, with the same strength,” he explains.
Challenges
All three professionals agree that while the weather creates a challenge, it is the logistics that is the greatest to overcome.
The proximity to busy roads within a built-up area poses multiple challenges, as there is the noise component to deal with, compounded by limited access to site, creating little to no laydown area.
“We are at the early stage of the design development, so we have brought Solid Green on board to advise us on how best to optimise green building principles.”
“We were fortunate not to encounter any groundwater on site as this would have severely impacted the founding conditions for the piles as, if there had been significant groundwater, we would have had to bring in dump-rock to create a drain aquifer, as well as a platform on which the big machines would work.”
He refers to the lack of space on the confined site and explains that an arrangement was made with a nearby office to use their boardroom for meetings and their parking area for their cars. Devan continues: “The piling operation will continue for another three weeks and then Mega Pile Inland would have completed their scope of works as a specialist subcontractor responsible for the piling and lateral support contract. The main contractor to undertake the superstructure and complete the buildings, is recently appointed Tiber Construction, due to start in May.”
“Previously, dry Shotcrete was used. This new wet Shotcrete is an innovation; it reduces wastage massively and also produces a more consistent mix.”
The value of the development is in excess of R120-million to R130-million, Devan says, and adds that the project is aiming to optimise the ‘green’ effort. “We are at the early stage of the design development, so we have brought Solid Green on board to advise us on how best to optimise green building principles. We have commissioned a borehole on the site and with respect to water reuse, there will be subsoil drains to catch any water generated by seepage, for recycling. It will be a function of how much is generated, as well as the quality.”
Bulk earthworks commenced after the builders’ break in January 2018, with the intention to complete the entire project by July 2019. Devan has only praise for the interaction the project has had with the authorities: “Surprisingly, the municipality has been extremely cooperative in respect of permits and so too, JRA has been collaborative with regard to truck movement in a congested area,” Devan stresses.
Comment
Asked to comment on the industry generally, Devan muses, “I think we have come out of a quiet period from an office development point of view, having been awarded two large projects in the Sandton area. After that, the industry quietened down a little; nevertheless, there is a general sense of optimism in the construction industry.” To a large extent, he attributes this optimism to the new political order and adds that the industry is looking forward to the construction sector being reignited. “Talking to all stakeholders within construction, from suppliers, contractors, and clients to developers, there is a positive sense of anticipation,” he assures. Alford explains thatMega Pile Inlandhas recently established an office in Johannesburg after its managing director, Greg Whittaker, decided to break away from the Durban branch. “We have only been in Johannesburg the past five years and we are extremely busy with a good client base, mostly as a result of our good reputation, since establishment in 1996.
“We buy only world-class geotechnical equipment, with brands like BAUER, Casagrande, and Comacchio, in order to stick to our motto of ‘Delivering INNOVATIVE Geotechnical Solutions’ for our clients. “Hiring only works if it is a short-term project. If you’re going to use these machines all day and every day, it becomes more cost-effective to purchase reliable equipment,” Alford adds.
“This has been one of the few sites where everything has gone according to plan, with no need for night-time work on the site.”
But it is Moonsamy who best sums up the project thus far: “This has been one of the few sites where everything has gone according to plan, with no need for night-time work on the site,” he states with conviction. Oxford Road is holding its breath until July 2019 when, if all continues at the present smooth rate of progress, the completed project will grace this thriving thoroughfare and join the plethora of activity along its length.
Project: 96 Illovo
Type: Office
Client: Victhyme Investments
Architects: Lyt Architects
Project management: 3D Projects
Bulk earthworks: Harrogate Civil Construction
Piling and lateral support: Mega Pile Inland
Structural and civil engineering: Calibre Consulting
Mechanical engineering: C3 Mechanical Engineers
Electrical engineering: KKK Consulting
Fire consultant: Chimera
Green consultant: Solid Green