Piling high: Foundations for Al Maryah Central
PMV takes a journey to the centre of the earthworks underway on Gulf Related’s Al Maryah Central project
The UAE is known for its pace of development, but it is more than evident at the $1bn Al Maryah Central site in Abu Dhabi, where, after just seven months of work by two contractors, the enabling works are complete.
Al Maryah Central will ultimately rise five storeys above the causeways of Al Maryah Island, and four storeys below, including two levels below grade, yielding 214,000m2 of space across two flagship department stores, together with a sweeping mall in between them.
The shoring was executed by Bauer Equipment, the operating arm of the German manufacturer, while the piling was produced by NSCC — both presided over by developer Gulf Related, whose Raymond Hubbard, our guide and senior VP for project construction, notes: “We have 900 piles, and NSCC produced these in in basically six weeks. I was here in 2009 and 2010 to consult for ADAC, and NSCC produced 7,000 piles for the Midfield Terminal — so I really wanted these guys.
“We had to competitively bid it, but thank goodness they got it, because I’ve never seen a contractor produce like these guys. They are outstanding, and they’re walking away from here three weeks early, which really helps us.”
The entire project is being turned around in 33 months, employing a schedule that will heavily overlap the different contractors on site, with the aim of accelerating certain components of the project ahead of others.
Al Tayer Group’s anchor department stores — a Bloomingdale’s and the first Macy’s outside of the US — are assigned to go vertical first.
The aim of this is to allow ample time for their fit-out ahead of the hundreds of subcontractors that will descend to furnish the main mall’s 400 retail stores, 145 F&B venues, and 20-screen cinema complex.
Hubbard explains: “We’ve decided to take the two department stores straight up. They’ll be finished in six months so that the Al Tayer Group out of Dubai gets as much time as possible to handle the fit out.
“In the same six months, the mall will be back up to street level, but it will take another five months to take it up the other five floors to top it out at the height to the department stores.
“So the concrete structure will take 12 months, while we will have five concrete crews on the job: one in each of the department stores, and three in the mall.”
“The key was to get the two department stores up quickly, and get the elevators and escalators, the MEP piping and duct work popped through and operational for Al Tayer.
“Then the teams can concentrate on just finishing the mall itself,” continues Hubbard.
“We’ve got 400 clients and customers coming in there. The mall itself is not an issue: it’s a big box. But it goes from us managing one big contractor to managing 400 little contractors, and getting all of them to the finish line, done and signed off by the appropriate authorities — that’s a challenge, I can tell you.”
The project is also in part being dictated by specific features on the construction and interior design, which has resulted in the constant relocation of the cinema around the site.
Hubbard noted: “In the part of the building where there is a cinema, you have that added weight in a very specific area of the roof deck — so the piles under that have to be bigger. The structural engineers have had to change the size of the piles depending on where it’s going.”
In all, there’s a lot riding on the piling, which NSCC installed using four machines: three Bauer BG-28 drilling rigs, delivering 270kNm of torque and 330kN of push/pull force; and a Liebherr LB 36 drilling rig, delivering 410kNm of torque and 400kN of push/pull force.
The project is employing three sizes of pile casing: 900mm, 1,200mm and 1,500mm to provide the required friction (rather than bearing pressure) for the project’s overbearing loads.
Hubbard notes: “Friction piles are much larger in diameter, because what actually holds the building up is the skin friction as the sand grips the concrete cylinders — so the structural engineers figure out the facial friction and how many piles they’ll need to hold the building up.”
He adds: “Even a 900mm casing is a large diameter, so it needs a lot of torque, and the Kelly bar has got to be a lot stronger to cut from 600mm to 900mm and so on.”
Assuming the pile casings don’t get stuck, each individual drilling and case-driving operation takes an hour, with the rig buckets filling up with the soft sediment in less than a minute.
Symphony of soil
For the closing months of the enabling works, Bauer and NSCC had to work around one another, in a delicate ballet performance of equipment that reached its peak with 30 units on site, carrying out excavation, piling, dewatering, re-excavation and pile-cutting operations.
For various reasons, including issues with the utilities, the shoring works fell slightly behind schedule, so NSCC arrived on site before Bauer had completed the shoring in pursuit of the project’s aggressive schedule. Only the first cut of soil off the top was performed — leaving the remainder of the excavation for later.
Hubbard explains: “One of the reasons why I came over is because I push things very hard. The Gulf tends to execute consecutively; but Related and I like to overlap things.
“We could have waited until the excavation was done, and then put the piles in, but it made more sense schedule-wise to begin once they made the first cut.
“With the shoring contractor running behind schedule, we made the decision to put the piles in from the first cut — it was a very small premium to cut them off later, but we saved ourselves about four months.”
In line with the plan to see the two department stores go vertical first, the piles were first placed in these two footprints at either end of the site, before NSCC worked inwards.
Only Ramadan slowed down the rapacious rate of progress, but Hubbard notes that even then the project was still witnessing the pouring of 1,000m3 of concrete a night — using a combination of 42m-hose Putzmeister and Schwing machines from the concrete supplier — with drilling operations continuing by day.
Mire of Maryah
Shoring complete, Bauer continued with the excavation of the remaining 100,000m3 of soil on site, while installing de-watering wells.
“There are 32 dewatering wells across the plot. The extracted water goes through a filtration system and then the clean water gets dumped back into the sea,” notes Hubbard.
During the drilling, the site was also sufficiently saturated with seawater that the concrete delivered by chute into the piles was forcing out large quantities of water.
Hubbard comments: it’s a pretty messy operation when you’re below the water table.”
The final step for NSCC, once the second cut has been made, is the use of HYTEC T00400-131 hydraulic pile breakers from German-Gulf, using chisel heads to bisect the pile.
Hubbard notes: “We’ve got to go another four feet down and two feet out from each of the piles to pour the caps, and then the first parking level goes right across the top of that on grade. Because it’s below the water, it’s heavily reinforced to prevent the hydro-static pressure from raising the slab.”
The main contractor, Brookfield Multiplex, will then install the water-proofing for the site, running it under the slab, between the piles and the pile caps, and up the site walls.
Send in the cranes
A more advanced stage of the project, but one which Gulf Related has already had to prepare for, requires the installation of two pedestrian bridges — 50m long and 18m wide — traversing the road between Al Maryah Central and the parking for the Sowwah Square complex.
Hubbard explains: “We’re going to pre-fab the bridges on the ground, pick the structure up with one of the biggest cranes they have in the UAE (on to the causeway), and put it on to a crabber — which is an elongated truck bed with 25ft-circumference tyres.
“The crabber doesn’t have to turn, but the tyres can turn 90°, so that we can bring the bridges in sideways and then hydraulically jack them into place. It’s an interesting process that avoids tying up the roads, and it’s really good that UAE contractors have that capacity.”
The final twist of the project will be two contracts for the overbuild of Sowwah Square’s parking garages connected to the bridges.
Hubbard adds: “The bridges are going to be challenging, but the over-builds, while not big footprints, are also going to be pretty challenging. All in all it’s going to be really interesting when all these buildings are done — you’re going to be able to walk around Al Maryah Island without ever having to go outdoors.”
And with the $425m main construction contract now signed by Brookfield Multiplex, it is now time to go vertical — marching steadily toward the scheduled opening in March 2018.
“We are very pleased,” says Marcus Truscott, Brookfield Multiplex’s regional MD. “The appointment is a considerable achievement for our team to be working with Gulf Related.
“We were fortunate enough to be one of two contractors shortlisted and then asked to present a best and final offer. The process of converting a contract of this magnitude is never easy, but Related made it reasonably painless.”
With the award, Brookfield joins an all-star cast of design and consultancy parties on the project including: Gensler as the main architect; Elkus Manfredi Architects as the retail specialists; the Rockwell Group on F&B, AECOM as the local engineering partners; and WSP and Thornton Tomasetti as consultants.
Kevin Ryan, MD for real estate at Gulf Related, comments: “A project of this ambition, size and complexity needs technical expertise and large-scale mixed-use construction experience. It’s nine storeys over the entire plot, so there are complexities from a scheduling point of view. Part of the retail world is dealing with retailer-led changes that can lead to changes even when you’re already under construction. That’s different from a residential building, where you make your decisions and build it.”
Peter Anderson, development director at Gulf Related, adds: “Hypermarkets are normally the anchor, so it’s a different philosophy.
“Over Macy’s, the fifth floor is a sort of lifestyle and F&B concept; over Bloomingdales, a hotel lobby will extend out over the roof-top.
“In terms of the overbuild, we’re building a retail centre and park on one, and a sports and outdoor retail concept and park on the other.”
Ryan adds: “We actually planned it from the start. Al Maryah Central is not a joint venture, so quite a different development from Sowwah Square, but the planning concept included the mall and the overbuilds from the beginning, when we bought the land from Mubadala.
“It was a different philosophy originally. Before we came along, the overbuilds were planned as parks across the entire surface, and designed to support all the soil and trees.
“That’s a very heavy load — so it just worked out well that the structure could actually support a level of construction instead.”
Anderson notes: “From a construction point of view, that doesn’t mean we’re not interfering with those car parks.
“Because of local requirements for egress, we have to put in a scape course so that we’re satisfying fire and life safety of those over builds, but the car parks will remain fully operational the whole time.”
Ryan adds: “We’ve worked to build a really excellent inter-disciplinary team, and it will hit the deadlines, which is not common here.
“The typical mall runs late and opens with low occupancy. Here, as The Galleria at Sowwah Square, you’re going to walk in on the first day, and it’s going to be full.”