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Engineering geology of formerly glaciated and periglaciated terrains

Engineering geology of formerly glaciated and periglaciated terrains

This project aims to investigate the influence of past terrestrial glacier and ground ice formation and decay on the variability in geotechnical properties and behaviour of Quaternary engineering soils. Geological bedrock of the Oxford Clay Formation and clay-rich diamicton (till) in the geographical area of the English south Midlands is investigated in relation to the middle Pleistocene Anglian (Elsterian) glacial limit. The research is undertaken collaboratively between the departments of Geography and Engineering at the University of Cambridge, Arup and the British Geological Survey (BGS). It is funded by Arup and EPSRC. Multiple research and industrial stakeholders are helping to shape the research and include Network Rail and Highways England.

Quantifying geotechnical variability in the shallow geological subsurface and its influence on geotechnical design and infrastructure resilience, remains a major challenge for ground engineers. The effects of mid-latitude climate change during the Quaternary resulted in multiple phases of ice-sheet formation and decay including the British and Irish Ice Sheet (BIIS). Terrain Much of southern Britain remained beyond the influence of glacier ice but was subjected to repeated phases of ice-rich permafrost formation and decay within geological bedrock and Quaternary sediments.

Glacier loading, subglacial meltwater generation and ground-ice formation and melting result in changes in effective stress in the ground. Multiple changes in effective stress occur in response to repeated phases of glaciation and periglaciation. Consequently, geological bedrock and Quaternary sediments record a complex and spatially variable stress history which in turn influences their properties and behaviour under geotechnical design loads. This variability results in reduced confidence in the choice of appropriate parameters during geotechnical design and assessment of infrastructure resilience.

Fundamental properties including particle size distribution, plasticity, density, moisture content and mineralogy are investigated as they influence the subsequent behaviour of engineering soil when subjected to stress. Their behaviour in terms of undrained shear strength, compressibility and stiffness is investigated using isotropically consolidated undrained triaxial and 1D oedometer experiments and compared to published and unpublished data.

This project attempts to quantify the degree of spatial variability using a geological lithostratigraphical classification and its relationship to Quaternary Engineering Geological Domains (QEGD). QEGD are characterised on the basis of their interpreted glacial and periglacial history and the influence of differing degrees of post-depositional weathering.

Geological characterisation of geotechnical spatial variability provides a means of reducing uncertainty in the choice of appropriate geotechnical parameters for infrastructure design and resilience.

Triaxial stress-path experiments with measurement of small-strain stiffness at the British Geological Survey geotechnical laboratories

Triaxial stress-path experiments with measurement of small-strain stiffness at the British Geological Survey geotechnical laboratories