A walkover survey of a side embankment on the West Coast Mainline railway (UK) revealed significant movement of the twin-track; a waterlogged trackbed and general deterioration of the slope. Ground monitoring and investigations indicated that in addition to shallow washout failures and formation pumping problems at trackbed level, the embankment was at limiting equilibrium with progressive downslope movement occurring along a deep-seated shear zone ( within underlying strata of glacial till and

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... laminated clay (weathered mudstone/siltstone). Phreatic level increases during rainstorm events, in combination with winter groundwater maxima, induced artesian pressures on the underside of the steeply-sloping shear zone triggering step increases in shear displacements. Other factors included the gradual post-peak decline in shear strength due to creep; internal weathering; cyclic, transitory stress increases by passing trains and densification of the overlying embankment fill. The upgrade works reduced the hazard of further embankment movement affecting the track and comprised the installation of stabilising piles along the mid embankment-slope arresting the deep-seated slide (factor of safety, FOS = 1.2); the construction of an earth buttress and regrading works reducing the upper slope gradient (preventing shallower slips and wash-out failures, FOS ≥ 1.3) and improved site drainage.