Project Sheet: Gallows Point, Ynys Môn

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Client

  • Ynys Môn County Council

Contractor

  • Alun Griffiths (Contractors) Ltd

Works Undertaken

  • Site investigation to determine the cause of the landslip and the ground conditions
  • Design of the remedial solution,
  • Preparation of the Contract documentation
  • Preparation of the pre-construction Information
  • Part-time supervision of the construction works

Description of Project

Following a landslip occurring on the slope below the A545 road between Menai Bridge and Beaumaris, which resulted in cracking in the road, GroundSolve Ltd were appointed to undertake a site investigation to determine the cause and prepare options for the remedial works in October 2015. A preferred solution was chosen by the client, Ynys Môn County Council, and construction works commenced in late August 2016 by Alun Griffiths Contractors Ltd.

The preferred solutions comprised an anchored reinforced concrete beam, which is anchored into the slope to support the edge of the highway. Soil nails and mesh were then installed down the slope to prevent any further landslip occurring and undermining of the anchored beam. The soil nails were installed using drilling rigs on skids and operators using rope access techniques.

This option was a preferred solution for the following reasons:

  • It allowed construction to be undertaken under single lane traffic, hence allowing the road to remain open. Closing the road would have had a significant detrimental effect on the local community.
  • The anchored beam allowed the road to be widened by around 1.0m at this narrow pinch point at no additional cost.
  • The use of skid rigs resulted in mature trees being left in place and the soil nails installed around them, hence minimising any habitat damage.
  • The use of skid rigs also negated the need for scaffolding, which would be expensive but also would have been difficult to construct on a very steep unstable slope. Therefore, no requirement for scaffolding also removed significant health & safety risks.
  • The vegetation was only cut to within 200mm of the ground surface so it will be able to re-establish quickly without the need for hydroseeding and so reducing the potential for the introduction of non-native species.
  • No works were undertaken on the foreshore and so reducing any risk to the sensitive marine environment.
  • Soil nailing causes minimal vibration and so the solution satisfied the Wales and West criteria for the protection of their gas main.
Constructing the anchored beam
Constructing the anchored beam
Temporary Works. Liaison with the client and stakeholders at all the stages of the investigation, design and construction ensured that the remedial solution provided a robust solution with a 120 year design life, whilst still addressing all the concerns and requirements of the client, the community, utility suppliers, the environment and health & safety.
Temporary Works. Liaison with the client and stakeholders at all the stages of the investigation, design and construction ensured that the remedial solution provided a robust solution with a 120 year design life, whilst still addressing all the concerns and requirements of the client, the community, utility suppliers, the environment and health & safety.