The ground monitoring industry has made some huge technological advances in recent years, but understanding what the results mean is still essential for success. Julie-Anne Ryan reports.
It’s nearly two decades since the Heathrow Express tunnel collapse marked a devastating point in ground movement monitoring. But developments in monitoring capabilities in recent years means the problem that led to that event could be consigned to the history books.
The issues related to the need to both gather accurate data and interpret the results in time to allow the design team to respond have reverberated throughout the industry. The resulting changes and advances mean that the instrumentation and monitoring sector is now a technologically sturdy lynchpin in underground construction - to the extent that the market is said to be worth about £100M a year, and growing.
“The market is widening, getting more involved, because people are realising that it’s a tool they need, because they need to have a little more certainty,” says Rory O’Rourke, managing director at Datum.
That’s not to say the money is flowing freely, any more than it is in any other industry. Aidan Laimbeer, commercial manager at Soldata, adds: “With the current climate, everyone is being pinched for smaller margins. From the geotechnical point of view, those margins are smaller to start with, and we have had to come up with ingenious ways to save money, to provide better value. Not just cheaper, but more technically challenging ways.”
Arup director Duncan Nicholson said at GE’s annual Basements and Underground Structures Conference, that while demand for deep excavations was growing, new projects needed to make more use of instrumentation and innovative techniques to meet cost and technical challenges.
The biggest change in the sector over recent years has been in telecommunications, and this will play a major part in what happens over coming years too. “It’s been extremely exciting over the past two or three years,” says Testconsult technical director Simon French. “Now, a remote site can have live data simply because of 3G and mobile technology. The whole ethos is one of having information at our fingertips. If you have a bridge in remote Cumbria, just by clicking on a website you can get live data and see that everything is absolutely fine without visiting the site.”
“Monitoring gets a bad press, because people don’t know what they’re asking for, or they get something in place and then it’s destroyed by their construction work.”
Rory O’Rourke, Datum
Recent advances in digital instrumentation, such as digital levels and tilt sensors, mean that engineers can very accurately monitor the 3D position of something. For the last 15 years, in contrast, they have had robotic total stations - useful and responsive in their way, but not capable of submillimetre interpretation.
“More and more projects won’t have considered breaking ground without having some form of instrumentation in place,” says French. “It’s becoming the norm.”
But clients need to know what they want, warns O’Rourke, and many of them don’t really understand what they are asking for. “We have about 450 sites that we monitor,” he says. “The biggest ones know what they want generally but even they need advice from us. Big companies often don’t ask enough when it comes to monitoring.”
Monitoring these days is just as important on smaller schemes, and no longer has to be the preserve of large, flagship construction projects. Itmsoil business development manager Nick Slater pointed out recently that: “As well as providing real-time monitoring during the construction phase of work, systems can be used in geotechnical and structural applications to help asset owners understand risk and how this may impact on their business.”
Current trends on geotechnical projects reflect technological advances as well as financial considerations. The removal of one layer of strutting at Tottenham Court Road for Crossrail is saving time and money, according to Nicholson, who reported that shape arrays were being used for real time monitoring of the excavation, making sure that the reality matched predicted design deformations.
There is, according to French, a desire to have a genuine understanding of what’s going on, “rather than simply accept what the old textbooks say, which are pretty conservative”.
It’s that understanding that’s so vital, says O’Rourke: “Monitoring gets a bad press, because people don’t know what they are asking for; or they get something in place and then it’s destroyed by their construction work. They don’t give their consultants a chance to do it properly.”
There needs to be a dialogue between subcontractors and clients, he stresses: “Ninety percent of the work I have is single tender, because they trust me to give them the right advice. Sometimes that advice is that they don’t need monitoring.”
There are various issues and challenges with current projects, of course.
French points to some of the Crossrail work: “It is a changing project in as much as expectations are very high, so meeting the expectations of designers is pushing everything to the absolute knife edge. There is nothing like a change to make everything advance. It was on one of the Crossrail projects that we started using digital levels and till sensors because the conventional way won’t work.”
“As well as real-time monitoring during the construction phase of work, systems can be used in geotechnical and structural applications to help asset owners understand risk.”
Nick Slater, Itmsoil
O’Rourke, who has spent “probably three quarters of a million pounds” on computer systems and websites thatare continually being updated, still believes strongly that “people are preoccupied with technology. We have a wide range of products and services, but often I’m persuading people that they don’t need to have all that.”
With multiple hits at any given time, he says, the big problem is interaction. “Some people will find it too complex, some will find it too simple, some people are impatient with a two-second wait, others are impressed with the speed and immediacy of it all. You’ve got to know your client.”
Nonetheless, monitoring systems for construction projects must focus on displacement rather than trying to measure stress in the field if they are to deliver usable results, according to UCL emeritus reader Richard Bassett. Speaking at the recent GE Instrumentation and Monitoring Conference in London, he said: “Displacement monitoring is the best approach. Stress monitoring only tells you if the stress is going up or down, not whether the project is close to failure. Nonetheless, even with displacement monitoring, there is a need to be clear about what is acceptable and what is not.”
And it’s this clarity that’s key, says French: “There is an education process required. When the spec asks for real time monitoring I ask the client what they mean and they say ‘data immediately’. That’s when I ask: ‘what are you going to do with it?’ There is no point in having real time data unless you have real time reaction.”
Lambeer adds: “Early subcontractor involvement is essential. What the manufacturer says about the instrument, and what the actual performance rate of the instrument is, are two very different things.”
At GE’s conference Bassett said he would like to see more information published about situations where failure has started, but emergency response has recovered the project. “We cannot learn from these experiences unless they are put in the public domain,” he says.
Assuming that the learning and the finance are put in place, the sector is set to boom. French is clear: “It’s going to absolutely mushroom.
“Six years ago you wouldn’t be able to dream of what you could do with an iPhone. Project that into the future - the whole concept of information is going to be taken to another level. We’re currently working on an app for the iPad; for years we have been using Google as the key information source, but that now has a limited life because everyone is going to have apps.
“I do believe it will all be much cheaper as technology becomes more run of the mill.”
Wireless systems are accepted as being very much part of the future, but again their use needs to be part of a considered approach to technology - using the correct technology for the particular environment.
Lambeer believes that wireless is part of the new wave of tools that will reduce unnecessary intervention. “It’s time and cost effective but it also meets health and safety concerns - taking someone off site when they can do the job in the office,” he says. “However, sometimes you do need someone on the site who understands what’s going on, data will be meaningless if they don’t know what the critical processes are on site.”