The Cumberland Road Stabilisation Works were a reactive and preventative stabilisation scheme to reinstate a section of the old river wall following deterioration and collapse in some sections. The new scheme, supported by cast insitu piles, was designed to reinstate an old footpath, known as "The Chocolate Path", and also a section of the Dock Side Heritage Railway, which are both associated with the nearby historic Bristol Docks.
In addition to this reinstatement work, the scheme was also designed to provide protection to the adjacent Cumberland Road and mitigate the risk of subsidence of this busy and important thoroughfare used for connecting transport to the local Bristol Airport.
The scheme was delivered by a team consisting of Bristol City Council acting as Client, Jacobs acting as Designers, and Alun Griffiths as Main contractor. Tony Gee were also appointed as temporary works designers to assist in delivery of the scheme.
P J Edwards were appointed to install a variety bored pile sizes and types for the scheme which was split into 3 core areas; Area 1 being temporary works piles to provide a working platform for heavy plant required to install the permanent works piles, Area 2, a large diameter contiguous piled wall to support Cumberland Road, and Area 3 consisting of permanently cased support piles for reinstatement of the footpath and heritage railway lines.
Temporary Works Piling (Area 1)
The first stage of piling work was to install 255no 450dia piles to depths of 14.0m within a closure of one lane of Cumberland Road. These piles were to form the foundations for a RC slab to act as a working platform for a larger 85t rig for installation of the permanent contiguous piled wall required for Area 2. Rig selection was critical here to mitigate the risk of any further damage to the road so a small lightweight GEAX EK65 was selected. The piles were installed by CFA methods and in a sequence which reduced the risk of collapse to the existing road way by installing 3no piles at each end of the slip area and advancing inward to meet at the mid-point.
Contiguous Piled Wall (Area 2)
The contiguous piled wall piles consisted of 75no 1200dia piles at 1500mm centres, utilising 1300dia temporary segmental casing running along the line of the old collapsed inner dock wall. These piles were installed using our Mait HR260 Rotary piling rig. Due to the nature of the site access to the work area, which was restricted by the zone of collapse along the existing river wall section, PJE designed and fabricated bespoke cantilever working platforms to facilitate the safe installation of piles alongside an open edge. These piles also included the requirement for sonic logging to verify their integrity.
Rows 1, 2, and 3 (Area 3)
The next and final phase of the contract was to install 96 no. 750 dia, and 40no 600 dia, permanently cased piles in 3 rows incrementally moving out into the river. The first row was completed utilising the Mait 260 rig following on from completion of the contiguous wall piles giving the client both program and cost benefit.
Due to weight restrictions a smaller 45t rig, a Soilmec SR45, was used to install piles on Rows 2 and 3. As each row was completed PJE demobilised from site to allow for the construction of the main RC slab which would in turn act as an extension of the working platform to install the next row of piles.
The 750dia piles were installed with 13.0m long 813mm OD steel casing while the 600dia piles were installed with 13.0m long 660mm OD casings all procured by PJE.
For Rows 1 to 3 Thermal Integrity Profile Testing (TIP) was specified, which provided by Lloyds Datum/CemOptics presented time and cost benefits to the Client.