Mabey helps facilitate rapid and safe ten metre excavation below central London

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Leading bridge and engineering services specialist Mabey has joined forces with construction contracting company Cappagh and engineering consultancy Malachy Walsh & Partners (MWP) to enable vital repair works to a collapsed sewer on Burleigh Street, a busy London side street off The Strand, which flooded some nearby buildings.

Responding to an urgent requirement from Thames Water in December, Cappagh managed the 10.5m-deep excavation which was dug using a pole grab excavator for the first seven metres, then by hand for the final three. Contracted by Cappagh and working alongside Malachy Walsh & Partners (MWP) who designed the temporary works, Mabey provided ten levels of Shaftbrace – a four-way hydraulic bracing system – to safely and securely support the walls of the excavation while the sewer repairs took place.

They overcame several challenges throughout the 12-week project, including working with the local council to divert traffic on the busy London thoroughfare, and having to re-direct several utility pipes.

In Britain, there are now more than enough pipes and cables below ground to stretch to the Moon and back 10 times. In London, a third of these pipes were laid more than 150 years ago, so are extremely delicate, and often laid extremely close together. Given the complex network of utilities pipes in high-density urban areas like this, Cappagh dug a number of trial holes to establish the safest route possible. Several underground gas and water mains were identified, which needed to be avoided or re-directed for the repair to take place.

The project ran through Christmas, with the sewer successfully repaired by late February.

Paul Ferncombe, Operations Manager, Cappagh, comments: “Having worked with Mabey and MWP on several projects over the past few years, we drafted in their services feeling confident that they would be able to support this urgent and challenging excavation on a busy, utilities-heavy London street. Digging holes this depth must be approached with the utmost safety, which is why supporting the excavation with a reliable groundworks solution assured we could go as deep as possible, completely safe in the knowledge that the walls were supported throughout."

Dave Holland, Engineering Director, Mabey Hire, said: “Cappagh brought us into this project at an early stage, which meant that we could advise on the most cost effective and safe groundworks solution. With nearby buildings, including a hotel, at risk of damage, time was of the essence and, over the course of three weeks, we provided ten levels of the strong Shaftbrace solution to enable the complex excavation to progress at a safe and efficient pace.”

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