Knab Rock, Mumbles

Outcome:

A low cost geological visual and tactile inspection of the cliff and slope providing the client with an account of the condition of the rock slope. Recommendations on remedial works for further Geotechnical or other interventions to protect users of a pumping station.

Details:

Knab Rock. Mumbles, Swansea

The Carboniferous Limestone promontory at Swansea Bay, Mumbles, is as former sea cliff which is particularly vulnerable to weathering along mudstone partings. A pumping station was constructed at the base of the limestone cliffs many years ago and this construction activity exposed fresh beds of mudstone. Since construction the mudstone has eroded significantly, causing overhangs in the limestone. This erosion combined with faults and steeply dipping beds created an ongoing problem with rockfalls.

The client looked for ways to stabilise and maintain the slope and prevent further erosion and commissioned ESP to perform a geotechnical appraisal and provide recommendations.

Access to the cliff was difficult and where required a roped access team was utilised to undertake the geological inspections.

In view of the space restrictions trimming back the slopes in an attempt to achieve a more stable profile was not feasible. Recommendations on support works included the following:

  • Dentition – i.e. concrete works to provide support to critical key stones which showed signs of potential failure.
  • Rock bolting to support individual blocks for which dentition was impossible or inappropriate.
  • Netting to control loosening of weathered rock faces

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