Patterns of movement in the Ventnor landslide complex, Isle of Wight, southern England

Jonathan Carey, David Petley, R Moore

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Abstract

The patterns of ground movement were monitored within a large, deep-seated landslide complex at Ventnor in southern England, between May 1998 and June 2002 using automated crackmeters, settlement cells and vibrating wire piezometers. It was found that the landslide maintains a state of marginal instability, such that it is subject to continual very slow deformation. Movement is primarily on a low-angled basal shear surface at >90 m depth. The movement record shows a series of distinct deformation patterns that vary as groundwater conditions change. Continuous slow deformation occurs across the landslide complex at rates of between 5 and 10 mm/year. The background pattern of movement does not appear to correlate with local porewater pressure. Periods of more rapid movement (reaching up to c. 34 mm/year during the monitoring period) were associated with a period of elevated groundwater, although the relationship between movement rate and porewater pressure was complex. The patterns of movement and the landslide geometry suggest that the likelihood of a rapid, catastrophic failure is low. Future episodes of faster movement are likely during periods when porewater pressures at the basal shear surface are elevated above a critical threshold. Whilst the resulting surface deformation damages the town, it is unlikely to occur rapidly without significant changes to the landslide hydrogeology or the stress state within the landslide.
Original languageEnglish
Pages (from-to)1107-1118
JournalLandslides
Volume12
Issue number6
Early online date16 Nov 2014
DOIs
Publication statusPublished - Dec 2015

Keywords

  • monitoring
  • isle of wight
  • landslide

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