Project Sheet: Deganwy Castle



  • Colin Jones (Rock Engineers) Ltd.


  • Volker Steel Foundations

Works Undertaken

  • Identifying the high-low risk areas
  • Design of rock bolts/dowels
  • Identifying where the bolts/dowels need to be located to gain maximum stability

Description of Project

Deganwy Castle is a historic ancient monument in Conwy which recently underwent stabilisation and consolidation works organised by CADW.

Colin Jones (Rock Engineering) Ltd were appointed to stabilise two rock faces to the south of the castle. They contacted GroundSolve Ltd to do the calculations for the design of the dowels and bolts.

A member of GroundSolve Ltd joined someone from Rock Engineering on a site visit to inspect the slope. They climbed the rock face to identify the blocks which needed stabilising and locate the positions of the required bolts and dowels.

GroundSolve Ltd proposed the installation of 2.5m long solid bars into the rock face, ensuring that at least 2m pass into the sound rock mass behind.

As it is a historic monument, the visual impact needed to be minimal. Therefore, it was decided that, where possible, dowels would be used rather than bolts to make the finished work fit into its natural surroundings. Dowels act in shear so there is no requirement for steel plates. However, some rock faces needed additional support so bolts were used.

In total, 20 dowels were installed on one rock face, and the other had 10 dowels and 10 bolts.

The areas of highest risk were heavily fractured rocks, some having evidence of recent rock fall. A few rock faces had already seen the failure of the lower sections leaving overhanging masses. These required the construction of anchored buttresses.
However, some areas were inaccessible to large construction vehicles meaning that anchored buttresses weren’t suitable. In these locations, the rock face was netted using Maccaferri meshing.

Areas of unstable rock face cordoned off for safety
Areas of unstable rock face cordoned off for safety
Inspection of the slope during the site visit
Inspection of the slope during the site visit

Environmental and Sustainability Issues

Some of the more stable rock faces had mature shrubs growing on them which were potentially going to damage the rock. The growing roots extend into the joints of the rocks, loosening blocks causing instability.
Selected shrubs therefore needed to be removed as part of the work being done.


I am sure I can speak on behalf of Cadw and here at Opus that the quality of the work carried out has been exceptional and in keeping with the historical nature of the site. Your efforts and hard work, especially given the working conditions mother nature afforded you, are well appreciated.