Clifton Suspension Bridge

Constructed by Isambard Kingdom Brunel. In 2000, a narrow shaft was discovered under the south footpath. A small excavation revealed a second corresponding shaft under the north footpath, and in 2002, 12 large vaulted chambers linked by 600mm diameter shafts were discovered in the 33m high Leigh Woods Abutment of the Bridge.

The Clifton Suspension Bridge. On the far side is the Leigh Woods Abutment

Initial Investigation Techniques

Investigation Work

Falcon was appointed to assist in opening up and forming a doorway into Chamber 4 of the Leigh Woods Abutment. In order to carry out this work an exploratory core was put through at the lower level of the vault to determine the exact make up and thickness of the wall to the abutment.

A 76mm diameter hole was diamond cored through the wall using mining barrel to allow withdrawal of the cored material as a complete length. Results showed the exact wall construction to be sandstone internally and externally, with solid concrete between the layers and an overall wall thickness of 1800mm.

Left: Stitch drilling operation to form door opening. Right: Removal of sandstone to create opening

Stitch Drilling

Following the results of the investigation work, Falcon was able to commence work forming a door opening to provide access to Chamber 4. Falcon stitch drilled 70 number 102mm dia.holes/cores around the proposed door opening perimeter, with the cores taken to full wall thickness/depth.

Cementitious Anchors

Cintec anchors are installed around opening

To give additional support and tie together the external and internal sandstone, Cintec cementitious anchors were installed around the internal perimeter of the opening. Cintec anchors are a stainless steel bar enclosed in a woven polyester tubular sock, which will expand when cementitious grout is pumped into the sock under pressure. The anchors were installed 200mm from the external wall face and set at an angle to ensure they were not visible.

Left: View from within Chamber 9.
Right: Falcon operative wearing confined space equipment in Chamber.

Falcon took just 10 days to complete the formation of the door opening and the work met the approval of all parties involved including English Heritage and the National Trust.
On completion of investigation works, the sandstone blocks were carefully removed to the Clifton Suspension Bridge Museum.

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