Piffs Elm Overbridge carries the A4019 Cheltenham to Tewkesbury Road over the M5 at Junction 10. R&W was contracted, as part of the Area 2 supply chain team, to replace the bridge foundations – which were subject to thaumasite attack – with piled foundations.
Our team worked with Skanska over a six-month ECI period, developing a detailed programme for the works, including a comprehensive plan for traffic management works (including narrow lane running, Varioguard and SPECS cameras) and a robust target price that was subsequently agreed and accepted by Highways England (HE).
The project included significant temporary works to facilitate the design solution: (1) ground and cofferdam support to accommodate the pier foundation excavation, (2) bridge deck propping to support the existing overbridge deck (while the piers and foundation were effectively ‘severed’ and then replaced), and (3) extensive scaffolding to carry out the structural steelwork to the bridge abutment (sited at the top of steep revetments); to access the pier repair works; and to provide temporary access stairwells, allowing unhindered pedestrian access to the central reserve phase of the works.
Temporary works also included the detailed production of AIP documentation, and design approvals and checks, all of which were carried out by R&W and our supply chain team. We purchased specialist equipment for the scheme that allowed us to excavate the pier foundation within very tight working constraints. We installed sheet piles as part of the cofferdam works and 900mm diameter augered piles to form the new bridge pier supports.
A key challenge faced during this project was the limited headroom – a maximum four metre clearance – for the cofferdam installation and piling. We purchased specialist digging equipment and zero tail swing plant to carry out the cofferdam excavation, using the same equipment to undertake the extensive earthworks. We also recognised that additional specialist equipment was required for the pile installation due to the head room, and quickly identified the best supply chain partner to complete the work effectively.
The team used a phased approach to construct the new foundations, including the installation of proprietary products by the R&W team; this required specialist training to connect the reinforcement. The new, partially completed, pile caps were used to support the extensive bridge deck propping. This propping enabled the hydrodemolition and severing of the existing pier to be completed, making the old foundations redundant. We then constructed the new piers and connected them to the new pile caps, effectively forming a new bridge pier and pier foundation, which allowed us to remove the propping.
To minimise disruption to motorway users and local residents, we propped the deck of the overbridge and minimised the network we occupied, allowing traffic to flow over the M5 motorway throughout, except for two weekend closures when the ‘stitch’ works, connecting the old piers to the new foundations were undertaken. By adopting this approach we maximised lane availability and minimised disruption without compromising the completion time of the project.
We also proposed and used alternative repair materials, including sulphate resisting concrete that had rapid strength gain characteristics, reducing the concrete curing times. This methodology also enabled us to complete the project in less time and reduced cost.
We made best use of the reduced working space by installing an innovative temporary access stairway for the central reserve phase of the works. The stairway also provided the following benefits:
R&W also undertook extensive safety fencing, including slip-formed barriers along with kerbing, ducting, boundary fencing, stonework, structural steelwork, ducting, drainage, site clearance and surfacing.
The R&W team collaborated fully with the client and wider team throughout the project. The very early engagement of R&W and other key suppliers accelerated the pre-start approval works and AIP completion. We invested considerable time on ECI and the joint development of a robust price and risk register. We also shared office space to promote the collaborative, one team approach.
Agreeing to complete multiple structures schemes as part of a wider works programme for our client allowed the management costs associated with each individual project (including this one) to be shared out over several schemes. This added significant value in terms of experience while creating cost efficiencies.
The combination of ECI, collaboration, innovative working and pioneering approaches resulted in R&W completing the scheme six weeks ahead of the original construction programme – an 8% saving. This was a significant success with clear and obvious benefits to Skanska and HE.
Lessons learned from the project were jointly reviewed and taken forward to a similar scheme that R&W also undertook for Skanska. Installing the pile reinforcement and achieving the design lap lengths was a challenge due to the limited head room. By discussing the works, after completion, with our supply chain partners and Skanska, R&W’s solution was subsequently implemented on a follow-up project.
The site had numerous visits and audits from Skanska’s project managers and HE directors. All feedback was excellent and reports demonstrated that the works were completed to a very high standard.
This project demonstrates R&W’s ability to undertake high value complex civil engineering works requiring full collaboration, commercial robustness and innovative solutions.
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