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All major social tasks in the areas of housing, sustainability, climate adaptation or livability have a substantial underground component. The underground is already crowded and more needs to be added. In the meantime, much of what is already in the ground needs to be renovated or replaced. For both tunnels and cables and pipes, that leads to a substantial task. Brenda Berkhout, coordinator Civil within the COB Tunnel Program and Jarko van Bloois, coordinator within the Knowledge Arena for Cables and Pipelines, explain the tasks, impact and solutions for renovation and replacement in the subsurface.
"In the 1960s and 1970s, we saw a peak in the construction of infrastructural structures in the Netherlands. We see that peak now and over the next decade reflected in the renovation task for bridges and locks, and thus also for tunnels," explains Brenda Berkhout. "More than 20 tunnels are expected to need renovation in the next 10 to 15 years. We still see some new construction in the multi-year plans, but most of the available funds will be devoted to renovation in the coming period."
According to Brenda Berkhout, the fact that so many projects are taking place relatively in quick succession presents a wonderful opportunity to take a smarter approach to tunnel renovations. "Now is the time. Within the South Holland Tunnel Renovations Program (PTZ) - fitting within the national Replacement and Renovation Program - Rijkswaterstaat has deliberately chosen a sequential approach in which experiences from the renovation of one tunnel are immediately processed and applied in the next. ProRail takes a similar approach, using renovations of the Hemspoort Tunnel and the Willems Tunnel to learn for the benefit of subsequent renovations. Within the CDE network's tunnel program, several projects are underway that support learning from project to project. The idea is that we turn the current renovation task into an opportunity to reduce the need for renovation in the future."
Much experience has already been gained in recent years with the replacement and/or renovation of tunnel technical installations. The lifespan of those installations is shorter than that of the civil construction. "For the civil engineering part, there is an increasing need to understand what happens in terms of deformation and degradation," explains Brenda Berkhout. "To achieve a life span of a hundred years and more, maintenance of the civil components is necessary. The Netherlands has many immersed tunnels, where the joints in particular are crucial. We see that these are aging and we want to know what is needed to prevent damage in the next fifty years. The same applies to concrete renovation."
"We are on the right track," is Brenda Berkhout's interim conclusion. "There are research projects ongoing within the civil engineering part of the tunnel program that deal with various aspects of grouting problems. The insights we gained within earlier projects are already being used in ongoing renovations. Furthermore, Rijkswaterstaat is facilitating our participation in the renovation of the Heinenoord Tunnel so that we can learn from it for the benefit of other practical projects. In addition, we are now working with universities. Funding has been arranged for doctoral research into the deformation and degradation of tunnels. That program runs through 2030."
So there is a structural knowledge approach that is increasingly beginning to bear fruit. That does not alter the fact that, according to Brenda Berkhout, there is still something to be desired. "When it comes to monitoring, for example, we can still learn something from the approach in Asia. There, too, there are many immersed tunnels. There you see that there is much more budget for monitoring joints, deformation and materials. Monitoring is often seen as too expensive in the Netherlands, but the result is enormously valuable. In tunnels we see ongoing settlement, even in tunnels that have been there for decades, but we still don't really know why that happens. We ballast tunnels to make sure they don't float and yet tunnels sink year after year. We want to know how long that process continues and what deformation the structure may have. Structural monitoring helps us answer such questions."
The renovation task for tunnels is not limited to the grouting problems of the civil structure. Brenda Berkhout: "We also want to achieve maximum availability of tunnels. Simply because the Netherlands cannot afford to have tunnels closed for long periods of time for maintenance or renovation. Keeping a tunnel tube closed in one direction already causes enormous chaos in many places, let alone a complete closure for a longer period. That's why we want to ensure that in the future there is no need for large-scale, long-term renovations and unexpected maintenance does not occur."
In addition, the COB network, in which clients, engineering firms, contractors and knowledge institutes work together, is looking for more efficiency. Brenda Berkhout: "A good example is the Evolutionary path to uniformity project, in which the COB network is investigating how we can ensure that tunnels become more similar in terms of technology and management information. This will make renovations faster, smoother and more efficient, as well as making future renovations simpler and with fewer tunnel closures.
With the help of this kind of focused, practical research, we are working more and more integrally. This is also necessary because we are missing hands on. We really need to be more efficient with the people we have."
For cables and pipelines, too, the peak in construction in the 1960s and 1970s is reflected in today's replacement task. But there is more to it. The replacement task comes into play when cable and pipeline networks need to be expanded. The energy transition is leading to the reinforcement of the electricity grid and the construction of heat networks, while hundreds of thousands of homes must also be added in the coming years. Moreover, the peak in replacement of cables and pipes is less unambiguous than for tunnels, because the expected life span for the different media (sewerage, electricity, water, gas) is not the same. From the desire to avoid disruption and duplication of work and to combine work for different assets, this is a complicating factor.
The cable and pipeline sector sees opportunities to combine replacement and new construction to make a virtue of necessity. A difficult task according to Jarko van Bloois, who emphasizes that the subsurface is already so full that we need to start thinking and working differently. "Governments and grid operators had the basic premise 'anything goes.' But that era is really behind us. The replacement and expansion task not only coincides with the energy transition; measures for rainwater harvesting and the increasingly undergrounding of functions such as waste collection and parking also have a major impact on cables and pipes. And the demand for greenery in the city is increasing in response to the desire to improve quality of life. This makes the overall task even more complex. On the one hand, we have to deal with a growing underground space claim, while less space is available underground. Moreover, the number of stakeholders is growing, making it even more difficult to unite the various interests."
"We have passed the point where we can still regulate. The crowded subsurface makes that directing has become a necessity," continued Jarko van Bloois. "Until now, solutions are always only sought in practice; that is not a tenable situation. Strategic choices are needed, clear policy choices that prevent discussions in practice. By being clear in advance about what is and is not allowed, what requirements and preconditions apply, all stakeholders know where they stand."
"The existing situation in the subsurface can hinder the progress of above-ground projects considerably. On the other hand, clever use of the subsurface can actually help to achieve tasks. That realization will have to sink in with administrators and policymakers," says Jarko van Bloois. "We can no longer afford to let the subsurface be a balancing item. The interdependent relationship between topsoil and subsoil should be on the table at the start of every project."
The CDE network, in which governments, network operators and contractors are represented, approaches the tasks from different angles. Jarko van Bloois: "All research projects are part of the Knowledge Arena on Cables and Pipelines, a knowledge program of the My Connection foundation and the CDE, which is often supported at the project level by the Physical Living Environment Fund. In this we look at issues such as direction, factual knowledge, new ways of working and digital collaboration."
Whereas the tunneling program currently focuses on three main topics - civil engineering, digitization and sustainability (see box) - the Knowledge Arena is still very fragmented. "The 'Common ground for underground infra' analysis conducted in 2018 and 2019 provided a good picture of the status of and challenges for underground cable and pipeline infrastructure in the Netherlands," says Jarko van Bloois. "Even then it was clear that cooperation is going to become even more important, but also that it is still very laborious. That is why it was decided to start small, with practical, recognizable tasks. In this way, various research projects have been successfully carried out in recent years. For example, an extensive online reference work (growth book) has been created that provides insight into myths and facts about laws and regulations for cables and pipes. We have also investigated the real state of affairs with regard to the "jungle of regulations" in municipalities and the behavior behind the occurrence of excavation damage. The organization of a Knowledge Expert Day in 2021 and 2023 ensured that the results were shared and celebrated. All this means that trust and understanding for each other has grown and we can now take the next step."
Jarko van Bloois is referring to the more programmatic approach that is currently being developed. "We see that more attention is being paid to the subsurface in policy-making for spatial planning, such as the ambition to make water and soil guiding spatial developments. There is an increase in consultative tables, research programs, knowledge institutions and cooperation coalitions dealing with the subsurface. In order to avoid duplication, unremarkable ad hoc results, confusion and contradictory conclusions, and instead to join forces and create coherence, it is desirable to give the Knowledge Arena a more central place and to program research for the longer term."
"That does not mean, incidentally, that the Knowledge Arena will function differently," stresses Jarko van Bloois. "The short-cycle method of knowledge development in which research trajectories are broken down into intermediate steps and several deliverables per year will certainly be maintained. The industry is very positive about this, it makes the enormous tasks manageable and the research concrete and rewarding. What we want is to align the projects more with the ultimate goal - where will we be in 2030? - so that there is a coherent plan for the coming years. That gives a foothold and offers the possibility of long-term funding, thus better ensuring continuity."
Sustainability is receiving increasing attention in both the tunnel and cable and pipeline sectors. In the tunnels program, the COB network is working toward three overarching goals for renovated and newly built tunnels in 2030: energy-neutral in operation, maximum 50% primary raw materials through commitment to reusability, and tunnels as a demonstrable solution for climate-resistant and water-robust design. For cables and pipelines, research into sustainability was conducted in 2022 from the Knowledge Arena. With governments, network operators, consulting and engineering firms, suppliers and contractors, frameworks have been determined for drawing up successful sustainability measures. The elaboration will be taken up this year. More information can be found at www.cob.nl/tunnelprogramma and www.cob.nl/kennisarena.
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