Costing £14.8bn, the route will run more than 100 km via 38 stations and include 21 kilometers of new, twin-bore tunnels under central London. Eight custom-made, tunnel-boring, giant machines weighing 1000 tonnes each will work 24 hours a day excavating the ground and building the tunnel walls as they dig. The Crossrail trains will bring an additional 1.5 million people within 45 minutes commuting distance of London’s business district and carry 72,000 passengers per hour in peak times along the central section, which should be completed in 2018 and be fully operational in 2019.
A massive construction project such as Crossrail brings with it an abundance of noise and vibration challenges. The C501 Moorgate shaft is a 35 × 35 meter, 55-meter-deep hole excavated right next to the existing Moorgate Station. Reinforced concrete panels sixty meters deep are being installed to form a box below ground, which will house a new ticket hall.
The site is one of the most constrained on the Crossrail scheme and offers little opportunity for multi-tasking; each job has to be done one step at a time. In fact, space is so constricted that the main contractor, BAM Nuttall Kier JV (BNK JV), opted for modular accommodation erected on a steel grid on columns above the access points to the underground. The operating conditions, established with the City of London, are also complex in order to both limit noise impact and provide periods of respite to the different stakeholders day and night. Permitted noise levels vary up to 12 times throughout the day. BNK JV needed to be sure that the priorities and expectations of stakeholders were met while enabling the project team to make progress with construction and fulfill obligations to the local authority and project owners, Crossrail.
In addition, the site is surrounded by buildings – some listed (protected due to their heritage value). Moor House, one of London’s largest office buildings, various hotels, a school and an exclusive apartment building are all close to the construction site and have to be taken into account regarding noise nuisance. In such a built-up area there are also many sources of noise other than the construction at Moorgate – air, road and rail transport create significant noise disturbance as well as other nearby construction sites. This makes it a challenge not just to keep construction noise levels below limits but also, should a breach occur, to determine the cause.
Drilling down into the details of data
In order to deal with these challenges, BNK JV turned to acoustic consultants Anderson Acoustics for a real-time noise-management solution that would fulfill the Crossrail project’s noise pollution restrictions, and prevent operations being delayed. With advice from Anderson Acoustics, BNK JV chose Noise Sentinel, a subscription-based service that combines established monitoring practices with new innovations, such as continuous assessment and easy data sharing with stakeholders, to help industry manage noise impact in the community. Noise Sentinel records the audio when levels are high, allowing users to investigate noise breaches by replaying the noise and thereby determining if it was construction-related, and if so, take action to address it.
Construction shift teams are equipped with a duty phone that receives warnings or alerts from Noise Sentinel via e-mail and SMS so that they can react quickly to noise events above set limits. Cloud-based computing allows any member of the team to have access to web pages that detail real-time noise levels, historical noise data and alerts.
This robust and effective system is designed to take away the headache of monitoring from the construction team. Noise Sentinel is constantly monitored by Brüel & Kjær and any equipment failure is identified and quickly rectified without the involvement of the project team. So while Brüel & Kjær focuses on its expertise – noise management technology, the contractor team is left to focus on its core business – construction.
The system has continuously monitored noise around the site since November 2011 and has exceeded both the expectations of the City of London and the contractual requirements of Crossrail. The history of noise data from Noise Sentinel is provided to the City on a monthly basis to show the site’s noise performance. Regular meetings with environmental health officers then look at more detailed data. As a result, the construction team is seen to be a ‘good neighbor’, which will work well for future construction bids, and can get more done because they know what their real noise impact is and don’t have to worry about breaching noise regulations.
A winning team
BNK JV been awarded Crossrail’s Green Line Scheme award for the project and Noise Sentinel has not only won the UK Noise Abatement Society’s John Connell Technology Award, sponsored by the Institute of Acoustics, but also been shortlisted for the Environmental Initiative of the year at the 2013 International Tunnelling Awards.
Did you know
Two-thirds of the excavated material will be donated to the RSPB (Royal Society for the Protection of Birds) to create a new, 1500 acre reserve at Wallasea Island in Essex.