Demolishing preconceptions

26th March 2021


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Author

Robert Askew

Thomas Cleary, Greg Lewis and Daniel Brown share how the Costain-Skanska Joint Venture team is applying an environmental approach to HS2 demolition work around Euston Station

On HS2 Enabling Works Contract-South, the Costain-Skanska Joint Venture (CSjv) team and its supply chain have placed the environment front and centre of decision-making in order to push development in key areas around selection of equipment, material reuse and protection screen designs.

The location of the demolition work involved in the London leg of HS2 Phase One made it imperative for the team to reduce the impact of associated noise, vibration and air quality on the local community. The Euston Approaches Demolitions team identifi ed several ways it could reduce the impact of activities through the full integration of environmental specialists and constraints at the pre-planning stage, informing procurement, selection criterion and overall sequencing and methodology.

Material re-use

A key challenge from the demolition work was how CSjv would manage the volume of waste being produced. This was particularly difficult due to the congested road networks surrounding CSjv’s sites, based primarily around Euston Station in the London Borough of Camden. One of the first demolition projects was a former warehouse and a university architecture building. Working with the air quality specialist and the environment team, a procurement selection criterion was devised to reward those who submitted a proposal in which demolition arising would be retained on site and crushed into usable 6F2 (engineered fill material). Despite being constrained on all sides, with very little room for manoeuvre, the supplier John F Hunt delivered a top-down solution that crushed more than 70% of the material on the footprint.

This is now practice across the contract, and through a workshop on designing out waste we developed a strategy of crushing demolition arisings into aggregates for re-use on site under the WRAP Quality Protocol. This was used to create temporary vehicle access ramps, crane mats and haul roads, as well as being deployed as backfill to structures and platforms in order to facilitate the main works civils contract.

This approach has resulted in 175,000 tonnes of demolition arisings being crushed. This has saved more than 1,500 tonnes of CO2 equivalent (CO2e), compared to waste removal and subsequent importing of recycled aggregate, and taken away the need for waste removal and subsequent material delivery, saving nearly £5m. The strategy saved 39,000 vehicle movements associated with waste removal and material delivery, significantly reducing impacts on local roads and air quality.

The team’s co-operation with HS2 and the Environment Agency allowed multiple work package areas to be treated as a ‘single site’, facilitating the transfer, storage and re-use of recovered materials. This enabled further collaboration with Skanska’s IP Central Euston works and the SCS Main Works contract on adjacent sites.

"The location of the work has made it imperative for the team to reduce noise, vibration and air quality impacts"

Equipment selection and demolition screens

A large element of demolition is the equipment used to protect the surrounding environment. Traditionally, in an urban environment, a top-down demolition method would be used, with scaffold encapsulation to provide protection from debris. This involves lifting smaller machines (depending on the strength of the building) onto the roof and demolishing the building using percussive techniques (such as breakers), all behind a scaffold screen.

To minimise the noise and vibration of demolition, the CSjv team at Regent’s Park Estate pushed to reduce the use of scaffolding as a screen where possible. This meant larger machines could be used for demolition without fear of causing uncontrolled collapse. The team designed a bespoke curtain that could be hung from a crane and follow the path of demolition as it progressed. The curtain was developed with a built-in water supply to nozzles in the beam at the top, providing dust suppression.

The use of the heavier high-reach excavator allowed for a pulveriser attachment that was large enough to crush the concrete, rather than a breaker attachment. A top-down method would have required demolition with breakers, as the capacity of the floor slabs limits the size of the machines that can be placed on them. When modelling the predicted noise levels for the two methods, we found noise levels when using pulverising attachments to be 12dB less at 10m away than noise levels when using breaking attachments.

The lessons learnt are being transferred to the next works package, where the high reach excavator will be used again. This time there is a greater constraint on the works in the form of the railway approaches into Euston Station. The team has worked hard to ensure a long reach excavator can be used, to maintain the reduction of noise and vibration. Demolition with the high-reach cannot be done with a full scaffold wrap, but we needed a more predictable screening system than the ‘curtain’.

A shipping container screen has been designed for the power signal box demolition work, and is to be used in tandem with the demolition curtain (see above right). The fully enclosed container screen design gives Network Rail the confidence that passage of trains will not be aff ected, and gives CSjv and HS2 a more sustainable approach.

Thomas Cleary is project manager, CSjv.

Greg Lewis is senior environmental adviser, CSjv.

Daniel Brown is site agent, CSjv.

Image credit: Shutterstock

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