Insight: Underground infrastructure in the time of a climate crisis. What can we do to help?

Image credit: Emran Kassim

3rd article in a special underground infrastructure series

The most pressing challenge facing humanity is the climate crisis. How can we ensure that everyone has the ability to live comfortable and meaningful lives, while preventing further damage to the planet and atmosphere, and also starting to reverse negative impacts? Those stewarding the creation, use, maintenance, and (if appropriate) end of life of urban underground infrastructure do not bear the sole responsibility for addressing this challenge, but we do need to ensure that opportunities to contribute meaningfully to aversion of the crisis are capitalised on. This means minimising all future carbon emissions. In the simplest sense that could mean that we do not build any more infrastructure or maintain existing assets. However, we know that is not the solution since infrastructure is the lifeblood of society, with the social value of infrastructure being increasingly included in decision making to enable improvements in, or at least sustaining the level of, quality of life metrics.

Given the urgency of the climate crisis, carbon emitted now and in the near future also bears greater cost. This is in synergy with UK governmental budgeting rules, where the “discount rate” effectively makes money cheaper in the future, discouraging spending now and giving lesser value to benefits (financial or otherwise) that are accrued a long time in the future. Again, this could encourage us to do less now and more in the future. But at what cost? Some climate change impacts are already locked in. Urbanisation is increasing and more and more people live in cities, increasing the demands on infrastructure. Combined these effects have the potential to reduce resilience of infrastructure, risking them not delivering on their purpose, and hence providing declining social value. Hence there is arguably a conflict between embedding and improving essential resilience and minimising the accumulation of further embodied carbon through capital works and maintenance.

Or is there? Often the costs of developing or maintaining infrastructure are discussed, but rarely the costs of inaction. Not investing in infrastructure can ultimately lead to catastrophic failure. But even if that is avoided, fixing problems in a pro-active way is more efficient in both cost and carbon terms than being reactive. Underground infrastructure in particular can have high construction and maintenance costs due to the specialist nature of the environment, and the inability to divert services (be they rail, road, water, wastewater) elsewhere. Therefore, allowing a recovery situation to arise will inevitably result in greater financial, carbon and social costs. There is therefore a “sweet spot” for intervening in existing infrastructure to take action to increase their resilience and prevent loss of service. Some research work is happening to understand when this should be, but there remain uncertainties. How, and how fast, underground structures will deteriorate in current and future climate conditions still needs to be better understood. We routinely think about quantifying design life for steel through corrosion rates, but concrete and soil aged in aggressive conditions remains active areas of research. In addition, the cost and benefits in both purely financial, but also carbon and social terms still needs to be quantified. Overall, methodologies for all these aspects are not necessarily available.

Making the correct decisions to maintain cost, carbon and social value is also hampered by the lack of frameworks for taking those decisions. This makes the case to invest in resilience of infrastructure, including underground infrastructure, difficult. Firstly, the “Green Book” approach in the UK does not allow for accounting of value outside of the project being assessed. This neglects the inherent connectedness of all infrastructure and urban systems. Secondly, the approach is designed primarily for new projects and does not have a method for giving value to resilience improvements of existing underground infrastructure. Coupled with current demands for cost constraint in public spending this often means that action will be taken to reduce costs (and with it resilience) rather than to increase it.

The first conclusion of this piece is therefore that we need to equip decisions makers with the tools needed to value the costs and benefits associated with existing and new buried infrastructure that properly takes account of financial resources, carbon resources and social value across longer time scales and over as wide as possible system boundaries.

However, looking fully at benefits in multiple areas and timescales is not enough. We can also seek to actively minimise those carbon costs and maximise those social benefits. Lean design and low carbon materials have important roles to play, but I will look here at my special interest in maximising social and carbon benefit by increasing the connectivity of infrastructure by making it dual use. The Stormwater Management and Road Tunnel (SMART) in Kuala Lumpur’s central business district is one example of financial and carbon costs being deployed to achieve two purposes and hence offer better value. It cost 515 million US $ to construct, which can be compared with benefits accrued over 30 years comprising: 1.58 billion US $ flood damage prevention, and up to 1.26 billion US $ savings due to non-realised traffic congestion.

However, in times of climate crisis it would be desirable for our buried infrastructure to positively help reduce future carbon emissions. The most obvious way for this to occur is via use of buried structures for heat exchange and storage as well as for their original function. Heat decarbonisation is a massive issue in the UK. Heating still accounts for almost one quarter of national carbon emissions, and is particularly hard to tackle due to the need to enter and retrofit around 28 million buildings as well as make changes in national infrastructure. Use of foundations and retaining walls or basements related to buildings for heat exchange, and their connection to local ground source heat pumps is well established. However, despite trials of using buried infrastructure in the same way, the solution has not become popular. Recent work has tried to uncover the reasons for this difficulty in implementing buried infrastructure heat sources.

Several transport infrastructure projects in the UK (Crossarail, Northern Line extension, HS2 Phase 1) have discussed, commissioned studies and even commenced design of dual use new tunnels for thermal energy exploitation, but none have implemented the solutions. Consultations with parties involved in these projects suggests this is due to a combination of high capital costs that make it hard to meet government affordability tests and the challenges of interfacing with various heat users outside of the specific infrastructure project so that a return on investment can be both generated and guaranteed. There can also be reluctance for a transport infrastructure provider to also work as an energy supply company.

The first of these reasons speaks to the earlier discussion about the absence of methodologies to fully consider benefits of infrastructure beyond the specific project. This is further compounded by the nature of government. Different departments have responsibility for the budget for transport, buildings and energy security and supply. While the costs for new transportation tunnels are borne by the department for transport, if the tunnels become energy tunnels they also give benefit to other government departments which are not sharing in the costs. At the same time, in the UK, the Department for Energy Security and Net Zero is leading on the development of heat network zones, where heat networks are expected to be the lowest cost answer to heating decarbonisation. However, the methodology for developing these zones takes is relatively unsophisticated in how it takes account of the availability of heat sources. In particular, the potential to use heat from underground sources is not well integrated into the zoning models. The presence of, for example, transportation tunnels or buried water and waste water pipes which could be exploited for thermal resources are not considered at all. This disconnect at the heart of government and in major infrastructure projects leads to significant missed opportunities, e.g. for the low carbon heating of around 1,000 homes per tunnel kilometre.

The examples above which considered use of tunnel heat exchange for thermal energy were all new build projects. But the opportunities to make a different would be much greater if existing buried assets could be retrofitted for energy exploitation. For some old tunnels, e.g. London Underground, this will prove challenging due to the tight train-tunnel envelope, but there may still be opportunities in e.g. the track drainage which is accessed for periodic maintenance. Heat pumps have already been connected to hot air coming from tunnel ventilation shafts in London and this opportunity could be utilised further. The waste water network in particular offers substantial opportunities for retrofit. Previous conservative estimates suggest that between 80 and 140GWh/day of thermal energy could be harvested, or enough to heat over 4 million homes. Flooded historical and abandoned mine adits and shafts also offer excellent opportunities for re-use in various regions of the UK, with the Coal Authority estimating that one quarter of the UK population lives in an area that could access mine heat.

Again, why do we not adopt these solutions? Some of the same challenges arise about accounting for benefits over a large system size. But in the case of retrofitting existing underground infrastructure for heat there are also technical challenges to be overcome. How can the retrofit be carried out in a cost-effective way that does not affect existing service levels? All structures require maintenance for their resilience and taking advantage of these works to also implement the additional capacity for heat capture must be at the heart of any solutions. For example, water and waste water networks already suffer unacceptable performance levels in terms of leaks. Combining the lining or repair of these networks with adapting for heat transfer makes sense. There is also the possibility for additional benefit to be drawn from heat capture, for example in lowering the temperature of sewerage and reducing the rate of harmful processes than can lead to corrosion of components within the network.

Finally, how we account for and allocate the carbon benefit from dual use infrastructure needs careful consideration. In the same way as the costs of dual use infrastructure should be split between the benefiting organisation, the carbon benefits need to also be shared. But how much of the benefit should an infrastructure company take compared to the energy company which distributes the heat? Again, the answer will lie in considering our systems over wider boundaries. Artificial divisions are of course useful for planning and budgeting, but can otherwise give rise to artificial barriers for adoption of new solutions.

In summary, while the construction and maintenance of buried urban infrastructure is associated with significant carbon emissions there is also the potential to use that infrastructure to help reduce carbon emissions in other sectors as long as we take a broad enough and long enough view of the both the costs and the benefits and we fully account for social value outside of any individual projects. The more value we take from infrastructure, the more important their resilience also becomes, and developing the methods needed to value that resilience and balance carbon costs and benefits will be more important in the future.