Geological Field Trip to Landslip at Fairlight Cove, East Sussex
Several Southern Testing Engineers attended on the 17th of September 2017, a field trip organised by the South East Regional Group of the Geological Society, to a landslip at Fairlight Cove, in East Sussex.
Fairlight Cove village sits on 50m high cliffs. The geology comprises siltstones and mottled mudstones interbedded with thin sandstone layers of the Ashdown Formation (approximately 134 to 145 million years old).
In southeast Sussex, the argillaceous part of the Ashdown Formation is well-developed and a series of clay seams, the informally named ‘Fairlight Clays’, is well exposed on the shoreline cliffs at Fairlight Cove. Here, this argillaceous part of the Ashdown Formation comprises dark grey finely-bedded mudstones and mudstones, commonly red-stained, with abundant iron carbonate pellets at some levels.
Fairlight Cove Landslips & Cliff Erosion – Late 1990’s to Early 2000’s
Major landslip and cliff erosion events occurred between 1997 and 2005 to the east of Rockmead Road in Fairlight Cove village, which led to the destruction of five houses and the evacuation of several others.
Subsequent site investigation and mapping of the slipped area indicated a combination of deep seated rotational and shallow translational slope failure mechanisms developed within an adverse geological environment comprising low friction angle clay and mudstone beds and high groundwater levels and associated pore water pressures within the sandstone layers. Over time, the toe of the slipped mass was continuously eroded be wave action, causing further ground collapses and slippages seawards.
Fairlight Cove Landslip Remediation Scheme – 2007 to 2015
The landslip and cliff erosion remediation comprised a combination of the following:
- A series of 55 No pumping wells at 6m spacing and up to 30m deep, along Rockmead Road. The role of the pumping wells has been to decrease the groundwater pressures to acceptable levels for the cliff stability.
- Re-profiling of the land slipped mass and installation of a network of surface drains. The re-profiling assisted in eliminating ponding conditions and encourage vegetation growth.
- A rock berm 240m long constructed along the toe of the landslip at the shoreline. The role of the berm has been to dissipate the wave action and decrease significantly the effects of sea erosion to the cliff material.
- Local residents’ active involvement at every stage of the planning, construction and maintenance works of the stabilisation scheme.
We would like to thank Professor Roger Moore (CH2M and Chair of Applied Geomorphology at the University of Sussex) the South East Regional Group of the Geological Society and local residents of the Fairlight Preservation Trust for what was a very informative and interesting tour.