A465, Heads of the Valleys Road
The Challenge from the Client:
The A465 Heads of the Valleys Road, built in the 1960s, is being upgraded to dual-carriageway as part of a £220m scheme to improve safety, traffic flow and business links to the local area.
Our challenge was to install two parallel walls of sheet piles approximately 200m long, next to the existing A465, into a 2.0m rock socket with rock strength up to ~90MPa. This is some of the hardest ground sheet piles have been installed into by a Giken in the UK to date. Sheet piles were required to be installed into the rock socket to directly transfers loads from the raised carriageway into the bedrock.
The scheme was subject to various environmental restrictions; working inside the Brecon Beacons National Park, a Special Area of Conservation, a National Nature Reserve, multiple Sites of Special Scientific and Geological Interest and in close proximity to a scheduled ancient monument. There was also a requirement from the client to install sheet piles using a vibration-free method to prevent damage to the existing diverted River Clydach, which runs in a mass concrete channel.
One pile line was to be installed along the side of an existing embankment, the other within an existing road lane.
As sheet piles were required to realise a sufficient design life of greater than 120 years, piles were special ordered from the mill in Grade S430GP steel.
Health, Safety and Environmental Challenges
- Working adjacent to live carriageways
- Working on steep slopes
- Working near waters
- Working on split levels
- Pollution of waterways
- Uncharted / abandoned mine workings
- Global Slope Stability failure
- Strength and stability of sheet piles during piling
- Accuracy and recording of information
The Ivor King Solution:
To facilitate the construction of a split level carriageway between Brynmawr and Pont Harri, we designed and installed the sheet piles to anchor the raised level carriageway to the bedrock. This then formed the footings for a concrete structure to be built on top.
We mobilised two Giken Silent Pilers operating in Super Crush Mode to site to install ‘U’ sheet piles. We worked closely with AGD Equipment, utilising their crawler cranes to ensure drilling supplies were maintained.
Sheet piles were unloaded at one end of the site using our 70t crawler crane, with piles being transported via our 25t excavator. A single 40t telescopic crawler crane pitched the 12.0m PU32 steel sheet piles to both Giken machines.
By choosing the Giken Supercrush method, the northern pile line could be installed without the construction of a piling mat. The southern pile line was installed next to the live A465. The majority of the works were completed working from a piling mat constructed on a single lane of the old A465.
Super Crush Mode
Super Crush Mode or Hard Ground Installation method enables piles to be installed into difficult ground conditions. At Heads of the Valleys we encountered cobbles and boulders in a layer between 4 and 7 metres below the existing ground surface and were required to install piles 2.0m into a rock socket.
The Giken ECO700 Silent Piler was utilised to pre-auger 685mm diameter holes prior to installing sheet piles. This pre-drilling of the boulder and rock layers enabled sheet piles to be installed, using either 2 or 3 winged drill heads with tungsten cutting teeth. `
Following the pre-augering process, the Silent Piler pressed in piles whilst simultaneously augering, progressing down the already pre-augered hole and under-reaming the piles. Augering the minimum area of ground was necessary to enable pile installation, but ceased before the full depth of the pile was installed. The final 400 to 500mm was then pressed with the auger retracted, to ensure the pile had end bearing capabilities into the bed rock.
The Giken ECO700 has an in-built Press-in Monitoring and Data Logging System which was used for quality control purposes and to determine the depth of the rock socket. The logs show press-in force, auger torque and installation time, downloadable in PDF form from the on-board computers.
Given the sheer scale and critical nature of the work, close site management and support was allocated for the duration of the works. Utilising our fully equipped site office, key supervisors and managers were located on-site, with vital operational links backs back to central resources and systems back at Ivor King’s Headquarters.
Ivor King provided a fully trained and experienced workforce, with the requisite construction, plant operators, and where applicable, supervisor’s qualifications. Additional Official Giken training and advice was brought in to ensure our operators were using the optimum drilling technique in such challenging ground conditions.
All pile deliveries were undertaken using FORS Registered and Chapter 8 compliant vehicles.