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- PublicationPeat slope failure in IrelandRecent peat failures in Ireland in the autumn of 2003 at Pollatomish, County Mayo and Derrybrien, County Galway have focused attention on such events. However, peat failures are not a recent phenomenon with possible evidence of peat failures in Ireland having been identified as far back as the Early Bronze Age. This paper summarises the issues surrounding peat failures in Ireland that would be of interest to an engineer\engineering geologist assessing this geohazard. The distribution of peat throughout Ireland, its formation, and its typical characteristic properties are discussed. A review of historical failures shows that there is a relationship between run out distance and failure volume and that the majority of the failures are clustered at slope angles between 4º and 8º. It seems that the risk of fatalities from peat slides is relatively low. The likely casual factors attributed to peat failures are presented using examples of failure, including the recent failures at Pollatomish and Derrybrien both of which have been investigated by the authors. Particular attention is paid to shear strength properties of peat and the applicability of traditional soil mechanics. Given the uncertainties which exist about peat strength, a cautious approach to slope stability assessment is advocated together with identification of potential causal factors to mitigate against this geohazard.
1625Scopus© Citations 52
- PublicationAnalysis of the peat slide at Pollatomish, County Mayo, IrelandA major landslide event occurred at Pollatomish, County Mayo, Ireland in September 2003, during a period of intense rainfall. It comprised about 30 significant individual longitudinal planar type slides of peat and weathered rock. Relatively simple limit state stability analyses, using the method of slices and an infinite slope analysis, 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.
2065Scopus© Citations 36
- PublicationIrish peat slides 2006 – 2010The purpose of this paper is to present a review of peat landslide events in Ireland since 2003, when two significant events occurred. Since 2003, there have been at least thirteen such events. Several of these events included more than one slide. It is also likely that there have been unrecorded slides. It seems that there is an increasing incidence of such events but they seem to occur in clusters with intervening quiet periods. These clusters coincide with periods of intense rainfall. For many slides at least two causal factors can be identified. Primarily these comprised intense rainfall but human activities such as road construction and peat cutting also contributed to the slides. Detailed geotechnical testing of the peat, including laboratory direct simple shear tests (DSS), is reported for two of the slides. Back analysis of these two failures suggest that the mobilised strength of the material in the failure surface is similar to that measured in the DSS tests. However conventional geotechnical analyses need to be treated with caution as they fail to account for the complex interactions in the sliding surface and in particular the lubricating role of water.
1305Scopus© Citations 12