Temporary Works

A30 Bridge, London, UK

Project Brief

LSY Engineering Consultants Ltd was appointed by Cadent Gas Ltd to undertake structural engineering services associated with the upgrading of gas infrastructure located within an existing road bridge on the A30, London.

The project involved the inspection and assessment of existing gas chambers, valves, and associated pipework located within and beneath the bridge structure. In addition, new gas pipe connections required the construction of access shafts ranging from 3.5m to 4.2m deep, necessitating careful consideration of excavation support and temporary works requirements.

Our scope included structural surveys, condition assessments, temporary works evaluations, and recommendations to support the safe delivery of the proposed gas infrastructure improvements.

Challenges

The project presented several technical and operational challenges.The existing gas chambers and pipework were located within confined spaces, requiring all inspections to be undertaken in accordance with strict confined space working procedures. Access arrangements had to be coordinated carefully, including isolation of the relevant gas infrastructure and continuous monitoring of atmospheric conditions to ensure the safety of personnel entering the chambers.

The proposed access shafts were located in close proximity to the A30 carriageway, creating additional challenges associated with excavation stability, traffic management, and the protection of adjacent infrastructure. Maintaining the safe operation of the live highway throughout the works was a key project requirement.

In addition, the age and condition of the existing gas infrastructure required thorough assessment to determine whether existing chambers and supporting steelwork could be retained or would require replacement as part of the upgrade works.

Process

LSY undertook a comprehensive non-intrusive visual inspection under the supervision of trained confined space personnel. The inspection enabled our engineers to assess the structural condition of the existing bridge, gas chambers, supporting steelwork, and associated pipework installations. The survey identified significant corrosion affecting several elements of the existing steelwork, confirming that replacement of a number of components would be required to ensure the long-term integrity and reliability of the infrastructure.

To support the temporary works design required for the installation of the new pipelines, ground investigations and trial hole information were reviewed to establish the prevailing soil conditions and assess excavation stability.

Using the findings from these investigations, we carried out structural assessments and earth pressure calculations to determine the most appropriate excavation support system. Following our analysis, a temporary works solution incorporating proprietary trench support frames and sheeted excavation support systems was recommended as the safest and most practical option for the site conditions. Throughout the design process, close consideration was given to constructability, worker safety, traffic management requirements, and the protection of the existing bridge structure and surrounding assets.

Outcome & Lessons Learnt

The project was completed in accordance with the programme requirements while maintaining the operation of the A30 throughout the duration of the works.

The structural assessments and temporary works recommendations provided Cadent Gas Ltd and the construction team with confidence that the upgrade works could be undertaken safely and efficiently. The replacement of the deteriorated infrastructure improved the long-term resilience of the gas network while minimising disruption to road users and surrounding stakeholders.

The project further demonstrated LSY Engineering Consultants Ltd’s capability in delivering structural engineering solutions for complex utility infrastructure projects within constrained environments and live highway networks.

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