Analysis of the peat slide at Pollatomish, County Mayo, Ireland

Abstract

Publication information Landslides, 3 (1): 51-61Publisher Springer were used to model the slide and it was found that the features observed on site could easily be reproduced. These included confirmation that thin layers of peat could be stable on steep slopes but the margin of safety reduces rapidly under elevated pore pressure conditions. As was observed in the field, the analyses suggested the most vulnerable zone was the upper layer of weathered rock but that slides could occur in the peat if its thickness was appreciable. Careful site characterization is vital in such studies. Here efforts have been made to understand the effect of fibres on the peat strength and some sensitivity analyes have been performed to assess the critical engineering parameters of the peat.

Measurement, interpretation and recommended use of laboratory strength properties of fibrous peat

“…In other words, the decomposition of fibrous peat material reduces its level of structural anisotropy (Pichan and O'Kelly, 2012;O'Kelly and Pichan, 2013). However, not all fibrous peat deposits have a general cross-anisotropic fabric -for example, the fibres in upland blanket bog peat material are typically orientated and spaced randomly (Long and Jennings, 2006). Figure 4 gives a clear indication of the hierarchy in the extent of structural anisotropy expected for different botanical peat types of Polder Zegveld (the Netherlands), with the axial (e a ), horizontal (e h ) and volumetric (e vol ) strain values calculated from shrinkage measurements taken in the vertical and horizontal directions during air-drying of representative test specimens.…”

“…In an intact state, the peat fibres themselves have relatively high tensile strength and they also provide conduits for the preferential flow of water through the bulk material (Hobbs, 1986;O'Kelly, 2015a;O'Kelly and Pichan, 2013). For peat deposits, the fibre deposition and subsequent large vertical strains experienced during the onedimensional (1D) consolidation in situ produce an inherent structural cross-anisotropy (Helenelund, 1967;Landva and Pheeney, 1980;Yamaguchi et al, 1985a), the degree of which is dependent on the material's level of humification (Hendry et al, 2012), although an exception is upland blanket bog peat material (Long and Jennings, 2006).…”

“…In recent decades, engineering problems associated with peat deposits, such as failures of embankments (Den Haan and Feddema, 2013) and dikes (Bezuijen et al, 2005;McInerney et al, 2006;O'Kelly, 2008), large-scale slope failures (Boylan et al, 2008;Long and Jennings, 2006;Long et al, 2011) and wind-turbine foundation failures (Lindsay and Bragg, 2005), have focused much attention on the research of peat mechanical properties. Further, historically, some dikes and canals (e.g.…”

“…Numerous examples are given later in the paper to demonstrate these behaviours. An exception is upland blanket bog peat material, for which the fibres are typically orientated and spaced randomly (Long and Jennings, 2006), with no detected pattern in measured horizontal and vertical undrained tensile strengths (Dykes, 2008).…”

Irish peat slides 2006–2010

“…It is not continuous and bedrock outcrops at the base of the slide in several locations. The mineral soil is reminiscent of the "hardpan" at the Pollatomish site (Long and Jennings, 2006). The failure surface is therefore complex and thus does not easily lend itself to numerical modelling.…”