Characterisation and engineering properties of Dublin Boulder Clay—an update

In this paper, we present an update on the geotechnical characterisation and the geotechnical behaviour of the Dublin Boulder Clay, which is arguably the most important geotechnical material in the Republic of Ireland from an economic point of view. Despite its properties and the units within the material being well known, variations can occur, and detailed ground investigation is often warranted. The material is very strong and stiff and has a high content of coarse particles. Examples are given as to where triple tube rotary coring, combined with sub-sampling, can produce very good sample quality of the material for geotechnical testing. In situ testing is problematic though there appears to be some promise in shear wave velocity measurements and high-pressure dilatometer testing. Examples are given where the material is shown to behave very well in a wide range of geotechnical applications, e.g., for retaining walls and soil nails/ground anchors. Some examples of surprising behaviour of the material, e.g., unexpected rapid settlements and the impact of fissuring, are also outlined. Further work is required into the development of practical numerical constitutive models of the soil, especially for use in fully coupled undrained to drained analyses.