Characterisation of gravel deposits in the pre-glacial channel, Central Dublin

Abstract

This paper reports on the production of an interactive 3-dimensional model over a key section of a pre-glacial channel feature in Dublin City. Significant infrastructural developments, most importantly the Dublin MetroLink project, are planned in the study area. The model presented here represents a complex depositional environment produced by several discrete phases of glaciation and deglaciation during the Quaternary and is consistent with previous published reports on the area. The geology in the study area typically consists of a Quaternary channel cut into the Carboniferous limestone bedrock, an intermittent lower glacial till, a large fluvio-glacial sand and gravel deposit and an intermittent upper glacial till.The digital software used to manage and create a 3-dimensional ground model is described and is comprised of several commercially available modules. The digital 3-dimensional ground models are particularly useful as a single data repository which can easily be updated as new data becomes available. Interpretation of a large body of geotechnical tests confirmed the fluvio-glacial sand and gravel deposit is relatively non-homogenous but can be broadly characterised as a medium to very dense slightly sandy to sandy gravel. Simple index tests, such as particle size distribution analyses and standard penetration testing, are very useful for both material characterisation and interpretation of profiles, albeit the latter test results can be influenced by the presence of cobbles or boulders. Geophysical testing, especially shear wave velocity profiling, was shown to be a very useful characterisation tool in these deposits. The findings of this work are consistent with the overall understanding of the erosional features, pattern of glacial deposition and general geological history of the study area in Dublin.