SAICE Civil Engineering – April 2018 – Vol 26 No 3
April 1, 2018
Piling into the opposition
July 2, 2018
Basements’ best shot
The Shotcreting of the three-storey basement’s retaining walls ensures an even spread and consistency of application, and also reduces wastage by about 40%.
The massive piles will comprise about 40t of rebar to support the huge weight above.
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.
The first of 96 piles being drilled into the soft earth. The piles are various diameters, ranging from 500mm to 1.2m.
A ready-mix concrete truck gingerly negotiates its way down the ramp after the extensive rains.
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.”
Alford says: “The weather is a challenge. However, with projects of this size, the main issue is normally logistics, because the earthworks company needs to bring multiple trucks on site, while we want concrete on site and need a place to store our steel and equipment. If tight sites like this are not planned properly, it can turn into a mess. Even the on-site offices had to be removed once the wall had reached its optimum height.” He continues: “In addition, there is a substation on the site, which created a problem. Normally on sites like this, that area would be kept open, enabling us to erect a site office or create a laydown storage area. But on this site, we have gone down so deep that we needed to take the stuff off the top, namely, the site offices.
“Other than that, we are going well, and we are ahead of schedule. The earth is soft, which makes it easier for us to drill; the trim is easier for the Shotcrete, and the earthworks are easier as there is no rock.” “The main concern has been around the extensive rain that has fallen over a short period of time, waterlogging parts of the site, bogging trucks down in the mud,” Moonsamy adds. Harrogate has 10 trucks a day running backwards and forwards from the tip site in Midrand.
Devan concurs and adds that the tight programme also poses a challenge, exacerbated by the vast amount of rain, which causes all construction to be halted until the downpour passes. “Also, to achieve an A-grade finish of the building entails very strict specifications. We have to produce a quality product in a narrow time frame.
“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.
The proximity to nearby buildings poses a challenge on the tight site, which is void of laydown area.
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 that Mega Pile Inland has 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.
Dev Devan is the project manager at 3D Projects.
Dan Alford, Mega Pile Inland contract manager.
Pregan Moonsamy is contracts manager at Harrogate Civil Construction.
“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.
