Is the GCC’s high-rise community making the most of geotechnical tools?
With the number of high-rise structures in the GCC increasing, is the construction industry doing enough to keep abreast of developments in geotechnics? Fatima de la Cerna reports
At this very moment, the world’s next tallest skyscraper is being constructed in Jeddah, Saudi Arabia, roughly 1,676km from Dubai, the home of the current tallest building.
If all goes according to plan – or at least according to recent reports concerning construction delays – the Jeddah Tower will be completed in 2019 and, at 1km tall, will easily strip Burj Khalifa of its title.
While this promises to be a remarkable achievement for the kingdom and is – for the time being, at least – in a league of its own, Jeddah Tower is by no means the only high-rise structure in development in the region, much less the world.
According to the Council on Tall Buildings and Urban Habitat (CTUBH), approximately nine super-tall structures are expected to be completed in the Middle East this year. It’s the same number that saw completion in the GCC in 2016 – the year that CTUBH dubbed “the tallest year ever”, with 128 buildings higher than 200m completed worldwide.
But with all this attention being paid to just how high builders can go, is the same focus being afforded to what’s going on under the ground – to what’s helping to keep these architectural marvels upright?
Merei Mohammed, head of the structural department at Dubai Creative Clusters Authority (DCCA), says that this concern for foundation designs for high-rises is the reason the authority organised the 2017 International Conference on Recent Developments and Innovations in Geotechnics and High-rise Structures, which was held from 16 to 18 May, 2017.
He tells Construction Week that it has become increasingly critical to identify new technologies in geotechnics that can help engineers get more accurate results when studying soil and rock conditions and carrying out other activities related to foundation design.
“This is very important now, especially with the growing number of high-rise buildings and their corresponding huge loads,” says Mohammed, noting that while DCCA regulations adhere to established codes and standards when it comes to foundation work, the Dubai authority is open to approaches, applications, and designs that may vary from traditional practices – as long as the geotechnical engineers involved are able to defend their ideas with solid calculations.
This openness to innovations in geotechnical principles and solutions, however, is not a widely held attitude in the region, states Prof Harry Poulos, senior consultant at Coffey, pointing out that while gradual education can be seen to be taking place in the industry, many of its members continue to adopt a conservative approach to foundation design.
He explains: “We have a number of criteria that we try to satisfy in foundation design, and one of the newer ones is the issue of sustainability, which also relates to the issue of economy in foundation design.
“In Dubai, for example, there has been a tendency to be overly conservative with designs, which means more use of concrete – and that means more carbon emissions. I think we’re at the stage now where we are able to develop more economical designs, which will cut down the cost without compromising safety, as well as increase the sustainability of the foundations and the structures.”
Citing an instance of the conservatism he has observed in the emirate, he recounts having encountered some reluctance to account for the resistance provided by the rafts when analysing foundation requirements, pointing out: “That resistance, in some projects, can be quite significant, so we’ve been trying to persuade the municipality here to allow rafts to take some of the loads, so that there’s no need to design for the piles to carry all the loads.”
Offering a similar observation, Prof Rolf Katzenbach, director of the Institute and the Research Laboratory for Geotechnics at TU Darmstadt, in Germany, says that recent pile-load tests he’s helped to conduct have revealed that “nearly all foundations in Dubai and the rest of the emirates are heavily over-dimensioned”.
He notes: “They are certainly safe, but they would be just as safe if [their dimensions] were a little smaller – if they used less concrete and less reinforcement.”
Attributing this apparent conservatism to a lack of accurate data on actual ground conditions, he continues: “Our philosophy as geotechnical engineers, when it comes to our computations and modelling, is to get as close to the real scenario as possible.”
In a bid to get that data, Katzenbach says that a number of pile-load tests were carried out in Dubai, involving a significantly bigger sample than normal.
“Our idea was to conduct these extremely expensive pile load tests – each costs between $50,000 and $100,000. They were expensive because we’re talking about massive dimensions, at least 40m. We had to put 2m3 of concrete inside, as well as a lot of reinforcement, and that’s only for testing,” he explains.
Katzenbach says that such an expensive undertaking was necessary because the tests gave “a wonderful impression of the real behaviour of the rock mass” in the emirate, something that is otherwise difficult to acquire through ordinary testing, which typically involves small samples of the material.
“[Conventional testing methods are] not representative of the actual ground conditions because they’re much too small, and then engineers will have to make a lot of assumptions to get from the values in the laboratory to the real value,” elaborates Katzenbach.
He adds that the results of his team’s tests indicated that soil conditions in Dubai are much better than what has been specified in theoretical prognosis, thus supporting Poulos’ assertion that conservatism in foundation design needs to be reviewed.
While not everyone in the geotechnical community will be comfortable with the idea of spending $100,000 on pile testing, it does not mean that there are no other innovations in the field that can assist in the delivery of foundation designs that marry safety, sustainability, and economy.
Dr Andrew Smith, technical director of Coffey Geotechnics Limited, notes that while most significant developments in geotechnics 30 or 50 years ago were in the area of theoretical understanding of the field, current developments are in the area of practical applications.
“People are developing new forms of construction plants that can do things that they couldn’t before,” he says, adding: “For instance, walls can be constructed to greater depths in the ground. Also, we now have electronic instrumentation that allows us to get real-time measurements of what is happening in the ground, which we could not do 20 or 30 years ago.
“And of course, as soon as you measure something, you find that it’s behaving not quite the way you expect it to, and that’s when you start learning. I think that electronic technology is going to help us a lot, simply because it will allow us to find out more of what’s happening in the ground while we build things on it or dig things in it.”
These innovations and developments in geotechnics, concludes Smith, will be crucial in enabling members of the international construction community to create the super-tall structures to which many GCC developers aspire.