A combined field and laboratory investigation into the moisture dependency of Vs for a clay-rich railway embankment fill

Embankments that were constructed over 100 years ago in the UK are increasingly vulnerable to the impact of climate change. These embankments were constructed without standard compaction techniques and many are comprised of clay. The clay fill used in these embankments historically exhibited volumetric instability due to moisture variation. With climate change models projecting increased precipitation events in UK and Northern Europe, these embankments face a growing risk associated with their stability and serviceability. Consequently, establishing geophysical-geotechnical relationships through combined field and laboratory monitoring becomes necessary for characterising the moisture-dependent behaviour of embankments. Since V s is related to the soil stiffness, combined field and laboratory based geophysical monitoring can help assess and understand the embankment condition under varying moisture levels. Combined field and laboratory investigations that capture the moisture-dependent behaviour of clay embankments remain limited, particularly where geophysical responses are monitored under actual environmental conditions. This study addresses that gap by examining a railway embankment constructed from London Clay through a combined field and laboratory characterisation programme designed to evaluate the influence of moisture variation on its geophysical and geotechnical properties. In the field, V s measurements were obtained on four occasions using the Multichannel Analysis of Surface Waves (MASW) method and correlated with soil suction and moisture data recorded by sensors installed within the embankment. Complementary laboratory testing was carried out on reconstituted soil samples subjected to drying and wetting (D/W) cycles that reflected the in-situ suction range, enabling a controlled assessment of corresponding V s measurements. The laboratory response was then compared with in-situ geophysical measurements to assess their relationship. By establishing these links, the study demonstrates the relevance and necessity of integrated field-laboratory geophysical approaches for characterising the moisture-dependent behaviour of clay embankments, particularly those susceptible to seasonal or climate-induced instability.