The need for improved management of the subsurface

The subsurface is used intensively to support economic stability and growth. Human interaction with the shallow subsurface ranges from exploitation of resources, accommodation of utilities, harnessing of energy (ground source heat pumps) and storage of waste. Current practice of managing these shallow subsurface zones is far from ideal. Many subsurface interventions are preceded by feasibility studies, predictive models or investigative measures to mitigate risks or predict the impacts of the work. However, the complex interactions between the anthropogenic structures and natural processes mean that a holistic impact assessment is often not achievable. By integrating these subsurface infrastructures within three dimensional framework models, a comprehensive assessment of the potential hazards in these shallow subsurface environments may be made. Some Geological Survey Organizations (GSOs) are currently developing subsurface management systems that will aid decision making in the shallow subsurface [1]. The British Geological Survey (BGS) is developing an open Environmental Modeling Platform [2] to provide the data standards and applications to link models, numerical simulations and ultimately socio-economic models so as to generate predictive responses to questions concerning sustainable us of the subsurface

Influence of geology and hydrogeology on heat rejection from residential basements in urban areas

Urbanization and limited land availability have resulted in the increased utilization of underground structures including residential basements in largely populated cities such as London, with an average addition of 200 basements per year in some boroughs. Residential basements kept at a comfortable temperature level throughout the year significantly contribute to heat fluxes in the subsurface as well as an increase in ground temperature. Understanding the ground thermal status is crucial in managing the significant geothermal energy potential in urban areas as well as the sustainable development of the urban underground, and in maintaining the energy efficiency of underground structures. In this proof-of-concept study, a 3D finite element approach accounting for coupled heat transfer and groundwater flow in the ground was used to investigate the influence of ground conditions on the heat rejection rate from basements. A detailed analysis was made of ground, above ground and underground built environment characteristics. This study demonstrates that the amount of heat from basements rejected to the ground constitutes a significant percentage of the total heat loss from buildings, particularly in the presence of groundwater flow. The extent of thermal disturbance in the ground varies depending on the ground characteristics. The volume of thermally disturbance ground inversely correlates with the groundwater flow rate in ground mainly consisting of highly permeable material. However, a direct correlation exists when the thickness of permeable soil layer decreases. A larger horizontal to vertical ratio of ground thermal disturbance is observed when the thickness of permeable soil layer increases

Large-scale urban underground hydro-thermal modelling - A case study of the Royal Borough of Kensington and Chelsea, London.

The shallow subsurface of dense cities is increasingly exploited for various purposes due to the significant rise in urban populations. Past research has shown that underground activities have a significant impact on local subsurface temperatures. However, the resulting spatial variability of ground temperature elevations on a city-scale is not well understood due to the lack of sufficient information and modelling complexity at such large scales. Resilient and sustainable planning of underground developments and geothermal exploitation in the short and long-term necessitate more detailed, more reliable knowledge of subsurface thermal status. This paper investigates the impact of some common underground heat sources such as train tunnels and residential basements on subsurface temperature elevation on a large scale and highlights the influence of local geology, hydrogeology, density, and type and arrangement of the heat sources on ground thermal disturbance. To tackle the size issues and computational expenses of such a large-scale problem, a semi-3D hydro-thermal numerical approach is presented to capture the combined influence of underground built environment characteristics coupled with ground properties on ground temperature elevation within the Royals Borough of Kensington and Chelsea (RBKC), London. Numerical results show that the extent of ground thermal disturbance is mostly affected by geological and hydrogeological characteristics in permeable ground (River Terrace Deposits). Density and spatial distribution of heat sources, however, are critical parameters in ground temperature evaluation in highly impermeable ground such as London Clay Formation. The locality of temperature rise and potential ground energy within immediate impermeable ground surrounding heat sources versus significantly large extent of ground thermal disturbance in permeable ground, highlights the significant dependency of ground thermal state and geothermal potential at the studied site to the ground and underground built environment characteristics and necessitates a better understanding of shallow subsurface thermal state for a sustainable and resilient urban underground development.This work was funded under the Global University Alliance (Cambridge Centre for Smart Infrastructure and Construction, University of California, Berkeley, and National University of Singapore) and in collaboration with the British Geological Survey (BGS) (EPSRC reference: EP/N021614/1)

Development of unified geological model surfaces from legacy 3D models in the Thames basin catchment area

A proliferation of 3D geological models has been created by the British Geological Survey (BGS) over the last 15 years, following significant developments in software, hardware and modelling methodology. Modelling of the subsurface by the BGS has been widespread, ranging in depth from 1m to 15000m, and covering areas in the orders of 0.1 km2 to 100 km2. These models have been produced to increase our understanding of the subsurface environment and to help us communicate issues pertaining to it, such as geological hazards, water protection and resource management. For these reasons, particular focus has been drawn to the major urban areas of the UK such as the Lower Mersey Corridor (Liverpool to Manchester), the Clyde basin (Glasgow and surrounding region) and Thames basin (London and surrounding region). This has led to the development of a number of overlapping models in these regions and, since these models have been created for specific purposes and at varying scales, there has been little consideration given to ensuring that the individual geological surfaces within them are consistent from one model to another. Methodology has now been developed through the Thames Basin Cross- Cutting Project to amalgamate multiple versions of individual geological surfaces taken from existing 3D models, some of them overlapping, into a series of unified surfaces that represent the preferred geological interpretation at any given set of coordinates. The methodology alleviates some of the issues that have arisen with the existing models, such as different scales of overlapping surfaces (expressed as cell or mesh size), and the use of different subsets of the available records (boreholes/seismic reflection profiles/geological maps), commonly with different interpretations. This methodology has been tested on four key horizons within the Thames basin catchment area which are the stratigraphic tops and bases of the Lambeth Group and Chalk Group. The unified surfaces will provide a consistent representation of the subsurface for use by other modelling disciplines, including groundwater science. They will contribute to a whole-systems approach to climate change research, structural modelling, process modelling and palaeoclimate studies. They will also provide a starting point for future geological modelling that takes account of the work already done for existing 3D models, rather than one that goes back to the original data

Making geological data accessible to non-geoscientists : a 3D model case history from Glasgow, U.K.

The British Geological Survey’s 3D geological framework modelling of the entire Glasgow conurbation and surrounding River Clyde catchment, has been undertaken as part of the Clyde-Urban Super-Project (CUSP) and in partnership with Glasgow City Council and other local and regulatory authorities. The 3D modelling covers an area of complex glacial superficial deposits, overlain by heterogeneous anthropogenic deposits that reflect Glasgow’s industrial heritage, over coal-bearing Palaeozoic bedrock succession deformed by multiple faulting episodes. As such, the geology poses significant interpretive challenges for planners, regulators and engineers. The depth dimension of conventional geological maps is very hard for non-geologists to appreciate. As a result, decision makers rarely take full account of geoscience issues in planning and development; nor do they fully exploit potential subsurface assets. With the advances of 3D hardware and software, it is now possible to combine disparate geoscience data types for a wide range applications and scenarios and to display these data effectively, and in ways that non-geologists can easily understand and use to inform their decisions. Using several 3D modelling packages, but primarily GSI3D and GOCAD® workflows in tandem, we have created 3D models designed to ‘nest’ within each other. Lower resolution regional models (c.1:50,000-scale equivalent) therefore provide the context for higher resolution (1:10,000-scale equivalent), and ultimately site-specific, models. The geological framework models have been attributed with a wide range of parameters such as permeability, aquifer productivity and various engineering properties. They have also been exported to flow modelling packages to model time-series processes such as recharge and flow of groundwater and will be used to model migration of contaminant plumes and carbon dioxide. Man-made objects, such as tunnels and mine workings have been embedded as 3D objects and placed into the 3D geological framework so their relationships to faults and other geological structures can be examined. The models are already assisting in the design and layout of new subsurface infrastructure such as buried utilities, tunnels, and underground storage, as part of Glasgow’s regeneration and redevelopment. They will also help to accurately quantify resources and enable their sustainable exploitation (e.g. aggregates, coal). In particular, the models provide an excellent basis for assessing the sustainable extraction of heat, using ground source heat pumps, from mine waters in Glasgow’s extensive network of abandoned mines. 3D modelling is therefore placing geoscience data and knowledge at the heart of the decision making process. With these data in forms that are interoperable with existing 3D models of surface infrastructure, the vision of an integrated 3 dimensional surfaces and subsurface approach to future city-scale planning is becoming achievable

The 3D characterisation of the zone of human interaction and the sustainable use of underground space in urban and peri-urban environments : case studies from the UK

Meeting the challenges of sustainable development and regeneration to support city growth requires the provision of attributed 3D geological and geotechnical data, information and process understanding in the urban subsurface. This provides a 3D framework for the characterisation of the spatial variability of the properties and processes within the shallow subsurface to aid sustainable land use planning and regeneration. The subsurface has to provide the resources and ecosystem services to sustain and create economic growth and meet societal needs, now and in the future while minimising the environmental impact of development. The 3D variability of the ground results from anthropogenic (man-made) processes as well as geological. Human exploitation of the subsurface and rapid land use change in response to population growth and urbanisation, result in temporal and spatial modification of the ground. The integration of 3D geological and anthropogenic deposits models is therefore essential for the characterisation of urban "zone of human interaction" and its response to anthropogenic environmental change. Model integration to aid land use planning has been applied in the formerly heavily industrialised cities of NW England and Northern Ireland to provide a basis for linear transport assessment, urban planning and the assessment of aquifer vulnerability

Effect of anthropogenic heat sources in the shallow subsurface at city-scale

Rapid rates of urbanisation are placing growing demands on cities for accommodation and transportation, with increasing numbers of basements and tunnel networks being built to meet these rising demands. Such subsurface structures constitute continuous heat sources and sinks, particularly if maintained at comfortable temperatures. At the city-scale, there is limited understanding of the effect of heat exchange of underground infrastructures with their environments, in part due to limited availability of long-term underground temperature data. The effects of underground temperature changes due anthropogenic heat fluxes can be significant, impacting ventilation and cooling costs of underground spaces, efficiency of geo-energy systems, quality and quantity of groundwater flow, and the health and maintenance of underground structures. In this paper we explore the impact of anthropogenic subsurface structures on the thermal climate of the shallow subsurface by developing a heat transfer model of the city of Cardiff, UK, utilising a recently developed semi-3D modelling approach