Emergency Work to Ladies Walk, Cardiff Castle

Cardiff Castle is a Grade I listed structure of cultural and historical significance. A major conservation and restoration programme has been underway since 2001. The initial priority was to make the structure watertight ahead of the construction of new visitor attractions inside the castle and its walls.

Ladies Walk forms part of the outer wall of the castle, believed to be part Roman, and constructed from random stone with a variable rubble core. The top of the wall provides a walkway at high level to the main house. As part of a thorough examination of all the masonry a laser survey revealed considerable variation in the thickness of the wall ranging from 3m to 4m tapering in towards the top and bulging in certain sections. It is thought that water penetration from the walkway above had caused fine material to be washed out particularly towards the east face creating voids behind the facing stone.

The consultant, John Mann of Mann Williams Consulting Engineers, determined that while the core of the wall was

stable the outer faces required tying in to prevent any outward movement and trial anchors were installed and tested as part of the pre-tender qualification process.

Bersche-Rolt won the contract to install horizontal anchor ties within the wall by competitive tender, which was let through Project Managers, Parry & Dawkin on behalf of the client, Cardiff County Council.

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Conditions of the contract included a strict twelve week contract period and that the anchors have minimum visual impact on the structure.

In total 1200 Bersche-Rolt anchors were installed in the wall, ranging from 1.5m to 4m in length. The heavy duty anchors, consisting of high yield stainless steel reinforcing bars with stainless steel spacers inside a semipermeable sleeve, were installed in holes formed with diamond tipped core drills and bonded in place with a specially formulated cementitious grout.

The anchor and sleeve are inserted into the wall and grout is pumped into the hole at a controlled pressure. Sufficient grout is forced through the sleeve to ensure a bond between the stone and the grout and hence the anchor. The expansion of the grouted sleeve intovoids and fissures also provides a mechanical interlock.

The sleeve is designed to contain most of the grout and prevent filling of the significant voids within the wall, which minimises changes to the fabric of the structure.

Metal detecting equipment was used to ensure that the core drill did not go completely through the wall and was calibrated to detect the drill head 40mm from the outer face of the masonry. Quality checks and pull out tests were carried out on randomly selected working anchors.

Bersche-Rolt LimitedStream House, Heron’s GhyllUckfield, East Sussex.TN22 4BY

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