Insight: Dealing with the Complexity of the Underworld, part 1

2nd article in a special underground infrastructure series

The Underworld

The underworld has two formally-defined connotations – a place under the Earth where the spirits of the dead go, and the part of society consisting of criminal organisations and activities. My interest (bear with me) lies only in the former, a term that evokes something poorly defined, something complex in nature; it therefore serves as a useful metaphor for those who study (interrogate, understand, map) the ground and what is buried in it, and then use this information for some purpose (exploitation, harvesting its ecosystem services, protecting something). When defining a major EPSRC-funded programme of research to address one of the essential challenges of installing or maintaining utility service pipelines and cables – understanding what is there before carrying out engineering works in this space, noting the common argument that we know more about the surface of the moon than we do about the top 2 metres of the ground beneath our urban places – we used the term ‘underworld’.

Mapping and Assessing the Underworld

The programme was called Mapping the Underworld and researched several different technological and organisational approaches to detecting, identifying and mapping in 3-D the shallow-buried infrastructure beneath urban streets. This was followed by a complementary programme, Assessing the Underworld, which sought to use similar approaches to determine the condition of both what was buried and the ground that supported it, recognising that a pipeline system performs structurally due to a combination of the competencies of both the pipe and the ground in which it is buried. This research led to and was complemented by a sequence of practical and Government developments, including the creation of industry guidance (e.g., the PAS 128 utility surveying standard), the National Underground Asset Register and the formation of the Geospatial Commission based in the UK Government Cabinet Office. Indeed, this activity has become further recognised as an issue of national importance by the establishment of a UK Government Foresight Future of the Subsurface project (GoFS, 2023).

Unsurprisingly, the British Geological Survey has been at the heart of all of this work, firstly as a project partner to the multi-university, multidisciplinary research programme, then a direct research collaborator, and now providing leadership on behalf of the Government by Holger Kessler to the Geospatial Commission and the Foresight project.

One of the many profound outcomes from this research was the conceptualisation of three interdependent infrastructures in the street corridor: the buried infrastructure (of whatever type), the surface transport infrastructure (typically a road structure) and the ground as the third infrastructure that connects and supports them both. Affording the status of ‘an infrastructure’ to the ground introduces the notion of initial structural competence, a change in structural competence as the context changes, and ‘deterioration’ models to define amended structural performance due to ageing if adverse physical or environmental conditions develop (noting also that consolidation and compression can improve performance – think shakedown theory). While geotechnical engineers readily understand the role of the ground, such terminology elevates the importance of it to the less initiated – it removes all notion that the ground is an innocent bystander in the functioning of two important infrastructure systems from any professional conversation.

Interdependent infrastructure systems

Sticking with the shallow subsurface and its relationship to the urban landscape, it can be argued that it underlies three broad categories of the surface: the built environment, the natural environment (the blue and green spaces that house the flora and fauna that make up urban biodiversity), and the street corridors that largely accommodate the arteries of our villages, towns and cities. The street corridors are the shared spaces in places where the urban metabolism operates most intensively – the flow of people, goods, resources and ideas, both above and below the surface. Engineers have a responsibility to make this urban metabolism, via the many different physical infrastructure systems that support it, operate both efficiently and effectively. This responsibility is complicated by the fact that these infrastructure systems are highly interdependent – their construction, maintenance and operation both affects and are affected by the other systems and, while working on one system there is a need to maintain the services the other systems provide. Factoring in the seemingly infinitely variable nature and properties of the ground and we soon arrive at a situation of considerable complexity.

Referring back to the underworld, and to paraphrase from Robert Macfarlane (2019) when referring to our relationship with the subsurface, the same three tasks recur across cultures and epoques: to shelter what is precious or vulnerable, to yield what is valuable, and to dispose of what is harmful or unwanted. He, like others, refer to our nature, and our description even, as being connected to the ground – the word human deriving from the Latin humanus, said to be a hybrid relative of homo, meaning man, and humus, meaning earth. Whether you agree with this or not, it is undoubtedly true that we rely upon the ground for both our survival and the successful operation of our society. We acknowledge its ability to grow the food we eat, and as engineers we would perhaps focus more on the trees and green infrastructure that we need to weave into our urban designs in some way to ensure that the ecological, health and well-being benefits they offer are not lost in the extensive constructed environment. We need to take account of, and make space for, tree roots. Moreover, we need to acknowledge the pervasive biological activity that occurs in the ground from the scale of bacteria upwards. As engineers, we often stop at simply acknowledgement, though with a slightly uneasy feeling that we ought to take greater account of this biological dimension in some way.

Exploiting the Underworld

The concept of ecosystem services perhaps provides a more helpful perspective. Ecosystem services are defined as the goods and services provided by ecosystems to humans and are commonly grouped into four broad categories: provisioning services, regulating services, supporting services and cultural services (Sadler et al., 2018). Provisioning (minerals, water, heat), regulating (temperature, enabling / limiting or preventing the flow of water) and supporting (strength, stiffness) are straightforward to interpret from a geotechnical engineering perspective, while cultural demands a little more reflection – ‘we bury our history’ is a starting point, yet there is a human connection with the ground that enhances our wellbeing. Such conceptions are particularly useful for three reasons: they reinforce the idea that engineering should seek to augment what the planet provides rather than replace it, that there are many forms of value that can be realised alongside the particular engineering requirements that we seek from our designs if we are aware of the full range of opportunities, and that when harnessing ecosystem services for our immediate needs we should recognise that (other and/or additional) future needs might need to be met from this same source (the ground with which we are working). It is in recognition of this that Price et al. (2016) describe “a methodology that combines subsurface characterisation, ecosystem service classification and future scenario analysis”.

Extending the notion that ‘we bury our history’, it is widely appreciated that construction in a built-up area might reveal unknown and/or unanticipated archaeological remains of some type. These include what previous generations have either left at the surface and then covered or consciously buried. They might be of cultural value at the time of burial or simply functional, reflecting societies and practices of their time. It is incumbent upon us to record, and perhaps retrieve or rebury, what we find so that the archaeological value is not lost. This dimension of the underworld adds both to the value equation that we should compile when creating and presenting the case for our designs and to the many dimensions of the context in which our work is carried out and to which our designs must speak.

Investing in the Underworld

One of the primary forms of value offered by the subsurface is underground space. As alluded to earlier, we bury things for several different reasons. Burial for protection and aesthetics combine in the form of pipelines – a partnership between structural elements and the ground to provide a stable and resilient conduit through which some resource can pass. By avoiding this activity on the surface or above the ground, it also serves to make places more sustainable and liveable (and what about ‘waste by pipeline’?). As also alluded to earlier, monitoring the condition of the pipe and ground, and carrying out maintenance when required, add to the pipeline’s sustainability and resilience credentials. A proactive approach applied to all infrastructure ensures continuation of functionality and protects the initial investment; put another way, maintenance itself is an investment and not simply a cost as many perceive it.

One prime example from the current UK research portfolio concerns Pipebots – the creation of swarms of small robots that will ultimately live within a pipe network and traverse it periodically to carry out a longitudinal programme of assessment of its condition. In this way, incipient failure – for example, the formation of blockages in sewers, formation of misaligned joints, cracks or other forms of progressive deterioration that might result in leakage – can be identified and dealt with economically before failure occurs. One reason why this programme is particularly important is that it has been suggested that there are more than 300 UK projects that have focused, or are focusing, on leakage detection from pipelines (i.e., once failure has already occurred and, importantly, once the ground has been affected by whatever has leaked). By adopting such routine monitoring, the industry would become proactive in terms of pipeline maintenance and thereby avoid the many adverse consequences, or negative value if you wish, associated with failures and emergency repairs. The business models, and hence business case, for such proactive action should surely be compelling.

None of this is a surprise, of course, to those of us who own buildings, gardens, vehicles, other mechanical equipment or, in fact, pretty well anything – we know we need to monitor, assess and maintain where necessary. Taking gardens as an obvious parallel, it is well known that growing and harvesting without ploughing back in organic matter and fertiliser of some sort results in steadily reducing productivity, quality and value of the outcome – maintaining the health of the ground is a necessary action, and arguably a responsibility if we do not wish to leave things in a poorer state than we found them. The thinking should equally apply to engineering soils.

Read more in part 2