Engineering in the Anthropocene
An understanding of younger stratigraphy is essential for engineering geologists, argues Ursula Lawrence
In the Autumn 2021 issue, Philip Ringrose highlights the importance of younger stratigraphy as we reimagine some geoscientific careers for the energy transition. Cenozoic, and particularly Quaternary and Anthropocene, deposits pose the biggest hazards to today’s civil engineering projects. Knowledge of these deposits is invaluable for keeping on track projects with design lives that are required to last more than 120 years.
In the UK, there are important Cenozoic bedrock outcrops in the London Basin. Over the last two decades, the majority of the big infrastructure projects (such as Crossrail, High Speed Two, Thames Tideway, Lee Tunnel and the Lower Thames Crossing) were constructed in and on these deposits, furthering our knowledge of the London Basin enormously. The London Clay Formation is an excellent tunnelling medium due to its strength, low permeability and relative uniformity, but its limited extent restricted London’s tunnels to the north of the Thames. Recent advances in tunnelling techniques have allowed the Underground network to expand into south London and the much more variable Lambeth Group.
Quaternary deposits occur throughout the UK. Glacial till often contains water-bearing, granular materials that adversely impact slope stability. Its thickness can vary enormously across buried valleys, impacting pile design, and it can contain shear surfaces that lead to slope instability. Fluvioglacial deposits form valuable aggregate resources—vital for use in concrete and drainage systems—but these can also vary in thickness and locally contain a lot of clay.
Relict Quaternary processes can continue to generate hazards. Cambering and valley bulging from over-eroded valleys can produce ground movements leading to voids and shear surfaces that can cause large settlements and slope instability. Periglacial processes can result in valleys containing soft, sheared material that can bring about slope instability or drift-filled hollows filled with water-bearing, coarse, granular materials that can lead to excavation instability, inundation, pile failure and settlement problems.
Anthropocene deposits potentially pose the biggest hazards. For example, prehistoric and historic mining has left partially backfilled mine-workings and quarries that result in loose backfill materials or voids. These cause excessive ground movements beneath structures and can destabilise excavations or slopes.
Old building foundations, especially at former industrial premises, can be substantial obstructions to new works. Prior site usage can result in chemical contamination that can spread with water movements, such as dewatering. Anthropogenic materials can be incorporated in new works if they are inert, or treated in situ and/or disposed off-site if they toxic or hazardous.
Engineering geologists acquire knowledge of younger geological materials and the processes that formed them through on-the-job experience, formal Continued Professional Development, and self-directed learning. However, university is an essential starting point: geoscientific and geo-environmental courses should be modified to provide a wide-ranging and detailed understanding of younger strata, not only in Britain but worldwide.
Dr Ursula Lawrence is an Associate Director of Engineering Geology for Capita Real Estate and Infra-structure and Chair of the Engineering Group Geological Society