The 2nd Hanrahan Lecture: Geotechnical properties of Irish compressible soils

Abstract

The objectives of this paper are to provide an update on work done and the development of knowledge on Irish compressible soils since Eamon Hanrahan's book on the topic. Eamon subdivided these soils into three categories; namely, alluvial, estuarine and lake-bed deposits, and he termed them ‘troublesome soils’. A brief background geology will initially be presented. The complexity of the deposits both on a macro- and micro-scale will be highlighted. Sites that have been well studied will be summarized and the engineering solutions used to construct on these sites will be reviewed. Although work on these sites presents a significant engineering achievement, some important lessons were learned. The remainder of the paper deals with how these lessons might be addressed in the future; for example, how to use modern ground investigation techniques to best characterize these complex deposits and what are the best techniques for examining important detailed aspects of 1D consolidation behaviour such as the identification of the apparent preconsolidation stress, the sometimes rapid rate of consolidation and creep, and also how to characterize the undrained shear strength of the soils. The work will be benchmarked against experience of the behaviour of Scandinavian soft soils.

The development and impact of an ice‐contact proglacial lake during the Last Glacial Termination, Palaeolake Riada, central Ireland

“…For example, at the southern end of Lough Ree, over 10 m of glaciolacustrine silt and clay underlies alluvium (Fig. 11A; Long and O'Riordan, 2001; Long, 2019) while the Lough Ennell basin contains glaciolacustrine deposits up to 14.5 m thick below Holocene sediments (Fig. 11B; Long, 2019).…”

“…11A; Long and O'Riordan, 2001; Long, 2019) while the Lough Ennell basin contains glaciolacustrine deposits up to 14.5 m thick below Holocene sediments (Fig. 11B; Long, 2019). Elsewhere, Van der Meer and Warren (1997) record glaciolacustrine clays up to 5 m thick under Clara Bog, as do Carney et al .…”

“…Further evidence for a former glacial lake includes the presence of glaciofluvial deltas and subaqueous outwash fans at the downstream end of conduit fills (eskers; Gallagher et al ., 1996; Delaney 2001, 2002a, b; Pellicer et al ., 2012, Delaney, 2019) and deposits of glaciolacustrine inorganic, laminated silt and clay that underlie the extensive peat and Holocene lake sequences on either side of the Shannon River and within the Brosna catchment (Van der Meer and Warren, 1997; Long and O'Riordan, 2001; Delaney, 2007; Long, 2019).…”