Ground stability and geohazards

Building damage in external wall.

  • How will the built environment (including regional infrastructure) be affected by changes in the physical properties of geological materials caused by environmental implications?
  • What are the implications for engineering development and geohazards in the future?

The physical properties of geological materials are incredibly complex and take into account their engineering properties, strength, ability to absorb water and other fluids as well as their susceptibility to compression, collapse, shrink or swell. These characteristics are strongly influenced by water content, temperature and frost, which in turn are influenced by weather and climatic conditions. It is absolutely vital, therefore, that we understand the impact of environmental change on the geosphere. In other words, what will be the physical response of the geology beneath us to the changing environment?

Improved understanding of processes and predictive modelling

Responding to these problems will involve consideration of wider issues including changes in land-use, trends of urbanisation, planning and potential changes in engineering practices, but could potentially contribute to an improved understanding of processes and predictive modelling.

More information on geohazards for the Thames basin area.

More specific questions that we are helping to answer:

How will extremes of the climate impact on shrink-swell clays in the Thames basin area?

The London Clay Formation is particularly susceptible to shrink-swell behaviour that has resulted in a long history of foundation damage due to ground movement across the outcrop. Damage has cost up to £500 m in a single year. Underlying most of the Greater London area, the London Clay Formation is of major engineering importance as it is on and within this formation that the majority of the city's infrastructure, buildings and underground services are constructed.

The volume change potential of a soil is the relative change in volume to be expected with changes in soil moisture content and the subsequent shrinkage or swelling can cause major damage to structures both above and below ground. Detailed statistical and spatial analysis of data across the London Clay outcrop has revealed a significant geographical trend in the volume change potential of this deposit, confirming an overall increase from west to east, but also showing subtle trends with depth. If the UK were to experience an increase in extended periods of dry weather, prior to future rainfall events, costs could rise significantly.

As part of an EU FP7 Pan Geo project, a polygon-wise ground stability layer of Greater London with an associated description document has been produced. The identification of geohazards was performed through combined interpretation of geological, land use and other geospatial layers, together with satellite persistent scatterers (PS) ground motion data for 1992–2010. This product identifies approximately 450 km2 of observed and approximately 1240 km2 of potential geohazards over London. Potential for natural ground movements (shrink-swell clays and compressible ground) is observed for the majority of the area. Geohazards observed through the PS data include both natural processes (compaction of the River Thames sediments) and anthropomorphic instability due to water abstraction and recent engineering works.

Recent research at BGS has analysed and modelled the relationship between climate and shrink-swell behaviour in order to increase understanding of the potential consequences of changes in precipitation and temperature on ground movement in the south-east of England during the coming century.

Analysis of historical climate data and comparison with subsidence claims data demonstrated the relatively close relationship of subsidence with two years' previous precipitation. A direct relationship with temperature has also been identified. To model a projection for susceptibility of south-east England to future climate change, forecast climate data were used and combined with BGS's national shrink-swell GeoSure geohazard dataset.

Preliminary results demonstrate the most noticeable increases in subsidence susceptibility are within the areas underlain by the London Clay Formation, with other clay-rich formations also being identified, including glacial till.

How will land subsidence and sea level rise interact in the Thames basin?

Long term planning for flood risk management in coastal areas requires timely and reliable information on changes in land and sea levels. A high resolution map of current changes in land levels in the London and Thames estuary area has been generated by satellite-based persistent scatter interferometry (PSI) aligned to absolute gravity (AG) and global positioning system (GPS) measurements. This map has been qualitatively validated by geological interpretation, which demonstrates a variety of controlling influences on the rates of land level change, ranging from near-surface to deep-seated mechanisms and from less than a decade to more than 100 000 years duration. During the period 1997–2005, most of the region around the Thames estuary subsided between 0.9 and 1.5 mm a-1 on average, with subsidence of thick Holocene deposits being as fast as 2.1 mm a-1. By contrast, parts of west and north London on the Midlands microcraton subsided by less than 0.7 mm a-1, and in places appear to have risen by about 0.3 mm a-1.

Is landslide risk likely to increase under climate change?

An improved understanding of cohesive shore platform erosion was sought through a collaborative project in 2005. The overall purpose of the research was to provide an improved understanding of cohesive shore platform erosion with a view to move towards best practice guidance. Achieving better guidance requires new data collection and improved predictive capability. New data are essential to improve our presently poor understanding of UK cohesive platforms, and to contribute to incremental improvement in predictive models.

As part of this data collection exercise, field programmes were designed at two contrasting platform-beach sites along the United Kingdom coast to collect samples and gather in situ data on geology, geotechnics, geomorphology and biology. The sites chosen were the London Clay platform at Warden Point on the Isle of Sheppey and the till platform at Easington on the East Riding of Yorkshire coast. These sites were chosen because they provide contrasting geological, geomorphological, geotechnical and biological make-ups. Two field campaigns were envisioned at each site, one to collect relevant data in the summer and one in the winter, to enable seasonal comparisons to be made.

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