New knowledge for old engineering structures
Expert(s) |
Joost Breedeveld
“We’re facing a monstrous task”, says Joost Breedeveld, researcher resilient infrastructure at Deltares. “In forthcoming years, more and more bridges, sluices, weirs, pumping stations and other sections of the waterways will reach the end of their lifespan, in any event, on paper.” Joost and his fellow experts Dick ten Hove from MARIN and Ad van 't Zelfde from TNO are developing a knowledge base with tools to assist administrators such as Rijkswaterstaat. This will give them an overview of the maintenance tasks for wet engineering structures and a perspective for action.
The Netherlands is a water-rich country, filled with thousands of hydraulic engineering structures. Many of them were built in the years before and just after the Second World War and, given their lifespan, are possibly 'exhausted'. In the meanwhile, transport, safety, agriculture, water supply and the economy are highly dependent on this water infrastructure. “Some engineering structures need to be replaced”, says Joost Breedeveld, “others can be renovated and sometimes the lifespan can be extended with more intensive maintenance. The costs of all these operations are considerable and capacity is limited, so we have to make choices. The question, however, is which choices are good.”
Research into corrosion
Together with TNO, MARIN and Rijkswaterstaat, the operating authority of many large, complex engineering structures, Deltares is working on the Knowledge Programme of Hydraulic Engineering Structures (Kennisprogramma Natte Kunstwerken, KpNK). “The KpNK must support the making of these operating authority’s choices with knowledge and tools to assess the engineering structures”, says Dick ten Hove, researcher at MARIN. “A good example is research into the corrosion of steel sheet piling, which have been constructed along canals, or as sections of sluices or weirs”, says Joost. “Due to corrosion – in real terms rust – the thickness reduces and therefore becomes less sturdy over time. Would there possibly be a smart way to measure how thick these steel sheet piles are?”
New measuring technique
“Until now, a technique based on ultrasonic sound has been used for such thickness measurements”, says Ad van 't Zelfde at TNO, the institute that developed this technique. “To do so, a diver must enter the water, because the surface must first be cleaned of fouling, the growth of algae, shells and other muck.” However, deploying divers is expensive and entails risks. A new technique, the Pulsed Eddy Current Testing (PECT), measures thickness by detecting the response to electromagnetic pulses. “There is no need to wipe anything clean for this”, says Ad, “so it can be done from the water’s edge, or possibly with submersible robots.” But before switching to another measuring technique, one needs to know if the techniques are equally reliable. “So we applied both techniques to a sluice that was to be demolished. Then we extracted the sheet piling and measured the thickness with an extremely precise laser measurement.” This research validates the new PECT technique, which in future, will allow sheet piling to be measured faster, cheaper and more thoroughly.
The knowledge programme must support the making of choices by operating authorities with knowledge and tools to assess the engineering structures
Dick ten Hove, shipping expert at MARIN
Options
“In some cases it still looks quite good even after fifty or seventy years, in other cases there are corrosion spots everywhere”, says Ad. If such measurements show that a longer lifespan is possible, then it can simply be maintained as usual, or more intensive maintenance can be undertaken to extend the lifespan further. “However, it may also be necessary to reinforce the sheet piling”, says Joost. “More extreme would be to extract the sheet piling completely and put a new one in its place. Or the choice might be made for an optimised construction with less steel, or made of timber. These are all options to be considered.”
Collision risks
“Another aspect is identifying the risks of collision at bridges”, says Dick ten Hove, an expert on ships at MARIN, “in seeking new methods to assess the likelihood of a collision and what the consequences would be.” The scaling-up of shipping, with ever more and larger ships, as well as stronger engines, plays a major role in this. Ten Hove: “One always assumes the worst situation, i.e. the biggest ship, with the greatest speed. That means wanting to be on the conservative side with the dimensioning, but that leeway is not always available anymore. So, we need to look at how the actual risks can be ascertained better. It means, literally pushing the boundaries a bit more.”
Imagine getting shipping to make a detour so that the ageing sluice gate does not need to be used at all, then that would make an enormous difference in costs
Joost Breedeveld, expert resilience infrastructure at Deltares
“Such considerations explicitly include the role that the engineering structure plays in the waterways network”, says Joost, “not every engineering structure is of equal importance. Imagine getting shipping to make a detour so that the ageing sluice gate is used less often or does not need to be used at all, then that would make an enormous difference in costs.”
Aside from shipping, factors such as water safety, the supply of drinking water and ecology are also included in such considerations. Another issue is preservation of the ageing weirs in the river Meuse, which regulate the water level in the Meuse for shipping. Joost: “The mechanisms with which the weirs are being lowered and raised, are starting to show defects, and they no longer comply with the latest European machinery directives.” A major renewal operation will have to be decided on in forthcoming years.
Climate change
In addition to the 'maturing warranty' of the engineering structures, there are also other factors that make the task of renewal pressing. “Climate change is creating more extreme situations”, says Joost, “which means more and longer dry spells with water shortages and wetter periods with flooding.” Given the history of the Netherlands, it has always been about the threat of high water levels. Ad: “But in 2018, we learned that drought and low water levels can be a problem too.” This is so, not only for shipping and the supply of drinking water and sprinkler water, but also for engineering structures. “Corrosion of dried-up sections could increase, and there is less fresh water available to prevent the intrusion of saltwater from the sea.”
Simulations
Facilitating simulations, e.g. an intrusion of the volume of salty seawater through a sea lock to the inland waterway when allowing ships to pass through, is also part of the KpNK programme. “The
knowledge gained is systematically analysed”, says Ad. “Drawings of older engineering structures are sometimes no longer available, but all kinds of data from various sources are available. If a hundred sluices are examined, how would you be able to compare these? And retrieving the essence from all that information, for example, to find where the problems mainly lie? The knowledge database plays a major role in such knowledge management questions.”
Drawings of older engineering structures are sometimes no longer available, but all kinds of data from various sources are available
Ad van 't Zelfde, TNO
The knowledge database is a website that is accessible to everyone. “One can select by type of engineering structure, and perspectives specific to the subject”, Joost says, “the nautical angle, the structural side, or the geotechnical side.”
Shared knowledge
All three KpNK researchers emphasized that hydraulic engineering structures are inherently interdisciplinary. The expertise at Deltares, TNO and MARIN is complementary. Breedeveld: “For a sluice gate, TNO has expertise of the steel and concrete, Deltares of the water and subsoil where it is constructed, and MARIN of the ships that make use of it.”
The shared knowledge is also collated in plans for practical research. Joost: “If a sluice has been amortised in full and must be demolished, this could possibly be used as a kind of testing ground. How instructive would it be to get a ship – also amortised – to crash through the sluice gate under controlled conditions. Then the consequences could be studied very precisely for the entire structure. A great deal can be learned from that kind of research. This is one of the wilder ideas that is being considered to provide operating authorities with better knowledge and tools for their preservation requirements in future.”
