The susceptibility of glacigenic deposits to liquefaction under seismic loading conditions: a case study relating to nuclear site characterization in West Cumbria

Abstract

Previous research has established a chronostratigraphy of glacial/deglacial events together with a lithostratigraphical framework for the Quaternary deposits of the Sellafield area in West Cumbria. The glacial record is dominated by sediments and landforms laid down during the deglaciation of the Devensian ice sheet. The Quaternary deposits are characterized by complex sequences resulting from oscillating ice sheet margins, changing glacial lake and outwash environments, relative sea level changes and glacio-tectonic deformation. The resulting deposits comprise sequences which possess a wide range of grain size, shape and sorting; some are normally consolidated and have very low to low in situ density. An understanding of the geotechnical behaviour of these deposits is critical during geological site characterization studies for the design of new buildings and infrastructure on existing and proposed nuclear sites. The geotechnical engineering behaviour of a sequence of glacial deposits on the Sellafield nuclear site is evaluated together with their susceptibility to potential liquefaction under certain seismic load conditions. The evaluation identified that layers of very loose to loose deposits within the ice sheet marginal landsystem are particularly susceptible to liquefaction under specified seismic loading conditions that are required to be modelled by the UK Office for Nuclear Regulation (ONR).