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Jennings, Paul
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Jennings, Paul
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Jennings, Paul
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Publication
Analysis of the peat slide at Pollatomish, County Mayo, Ireland
2006-03, Long, Michael (Michael M.), Jennings, Paul
A 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.
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Publication
Peat slope failure in Ireland
2008-02, Boylan, Noel, Jennings, Paul, Long, Michael (Michael M.)
Recent 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.
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Publication
Irish peat slides 2006 – 2010
2011-03-02, Long, Michael (Michael M.), Jennings, Paul, Carroll, Roselyn
The 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.