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

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.