CEEQUAL Excellent (90.1%) – Whole Project Award
Version 4, Jul 2015 | London, England, UK
|Highly Commended – CEEQUAL Outstanding Achievement Awards 2016 – Effects on Neighbours|
Assessors: Tom Howden, Mike de Silva, Jess Kennedy, Stephanie van der Pette and Dan Ibrahim-Webster
The C300/C410 works involve the construction of the western portion of the Crossrail eastbound and westbound running tunnels, including station platforms and cross passages, between Royal Oak Portal near Paddington Station through to the eastern end of the new Crossrail station at Farringdon, referred to as Drive “X” and totalling 6.5km of twin bore tunnel. The tunnels travel beneath central London, which comprises of a densely populated area of residential, commercial, administrative and heritage buildings plus particularly noise and vibration sensitive locations in Soho, the home of post film editing. The tunnels connect with Bond Street, Tottenham Court Road, and Farrington Stations, and as such have significant integration into the existing infrastructure.
The decision to combine the C300 (bored tunnel) and C410 (sprayed concrete lining) contracts was an added value proposal submitted by BFK, which not only provided construction efficiencies, but also resulted in a significant reduction in the removal of spoil via road from central London with consequent improvements in terms of construction traffic volumes, noise and air quality benefits and safety.
BFK’s area of operations was extensive, covering multiple sites across London and into Kent. The works included a segment manufacturing facility at Old Oak Common and Sprayed Concrete Lining works for tunnel platforms and cross passages at Tottenham Court Road, Bond Street, and Fisher Street. The project also included grout shafts, extensive utility works across London, and a waste transfer facility at Northfleet in Kent where all tunnel spoil was received for onward shipment to Wallasea Island.
Challenges and achievements
People and communities
Working in Central London through highly populated residential areas and adjacent to and under churches, theatres, recording studios, schools, and hotels presented a unique challenge. It required not only a significant investment in noise and vibration monitoring and management but critically an integrated approach led by the BFK Environment Team. This involved the Community Liaison and Construction Teams, an embedded team of noise consultants, and work alongside the Crossrail noise and vibration specialists. A multi-faceted approach was used to overcome the key challenges faced:
- Management of ground-borne noise and vibration from sprayed concrete lining works.
- Management of ground-borne noise and vibration from the temporary construction railway.
- Management of airborne noise impacts
Management of ground-borne noise and vibration from sprayed concrete lining works
Given the difficulties with accurate predictive modelling that was established early on, BFK adopted a risk based approach to assessing the risk profile of works on sensitive receptors. This involved proactive ground-borne noise and vibration monitoring, and identification of the sensitivity to works at different times of day of all receptors within 200m of work sites. This in turn helped inform the works planning community liaison work to enable improved communications and brokering of working hours agreements with key receptors such as churches, recording studios, and residents particularly affected. An early review of construction methodologies and adoption of a hierarchy of sprayed concrete lining demolition methods ensured that heavy equipment – associated with ground-borne noise and vibration impacts – was not used unnecessarily and low impact methods were used instead. Key benefits of this approach included:
- Improved prioritisation process for proactive ground-borne noise and vibration monitoring.
- Improved planning and phasing of works to limit disturbance.
- Improved community liaison and information management.
- Reduction of noise and vibration impacts.
Management of ground-borne noise and vibration from the temporary construction railway
To minimise impacts from 13km of temporary construction railway (used to support tunnelling operations), BFK adopted a range of mitigation measures to limit impact from ground-borne noise and vibration. These measures covered:
- Design and procurement: During pre-construction, BFK carried out extensive acoustic performance modelling in association with rail suppliers. This was followed by verification monitoring over a number of nights once the track was in operation. Together with the adoption of key Crossrail design elements for the track (vertical alignment thresholds and track jointed at 450 to prevent ‘butting’), the key outcome was provision of a versatile track where acoustic performance could be improved by switching up the track isolations pads where this was identified as necessary.
- Construction: Regular track inspection by track engineers ensured that the acoustic performance of the rail line was maintained. Track upgrades took place on two occasions following complaints from residential receptors. Track upgrades covered lengths of track 100m either side of affected properties. In one instance, the affected property was part of a residential block so, as a precautionary measure, the upgrade encompassed the entire length of the block and 100m east and west of the block, a total distance of 350m. The residents reported no further noise issues.
- Operation: Managing the speed of the rolling stock was also critical to managing ground-borne noise and vibration: the higher the speed the higher the noise and vibration. Key procedures put in place included:
- Variable loco speed zones to reflect the sensitivity of surface receptors.
- Automatic speed checks though different tunnel sections using automated data loggers.
- Spot checks using a speed gun.
- Fixed speed signage and lighting within the tunnels to delineate speed zones.
- Speed limiters on trains.
Ten construction trains were in operation in two tunnels for a year and a half, covering many thousands of kilometres under Central London and a range of highly sensitive receptors including recording studios and theatres. In all, a total of eight complaints were received, all of which were from residential receptors and all of which were resolved to the satisfaction of the complainants.
Management of airborne noise impacts
Designing out noise was the first stage for noise management and mitigation. Airborne noise impacts were eliminated through the review of works requirements, methodology, and plant. This was then supported by extensive adoption of noise mitigation measures (such as screening) and a rolling programme of automated and attended noise and vibration monitoring carried out by Anderson Acoustics in and around all sites. Measures included:
- Designing out noise: Adapting slab breakout methodology to remove large sections of reinforced concrete as blocks rather than break them up on site. This resulted in a reduction of heavy breaker use of 420 hours. This allowed works to progress within the S61 limits and all slab demolition works were completed in a six week period with only one complaint; a significant achievement considering the extent of the residential estate bordering the site.
- Noise mitigation: The installation of an acoustic barrier on the entire northern façade of a residential facility adjacent to Tottenham Court Road western Ticket hall which reduced measured noise levels by 10dB.
- Noise monitoring: Attended noise monitoring reporting was improved across all construction sites through the development of an iPad app by Anderson Acoustics to record all observations, noise levels, and images of site activity. Use of this technology enabled near real time reporting which proved very effective in complaints handling procedures where quick turn-around was required. At Bond Street station CCTV was used in conjunction with automated noise monitoring equipment to improve our ability to identify noise sources. This enabled better targeting of noise reduction training and also enabled the identification of noise being generated off-site, such as from local bars.
A huge amount of time was invested in eliminating, reducing and mitigating effects on neighbours, particularly from noise and vibration, through a collaborative approach between the BFK Construction Team, the Environment Team, BFK Acoustic Consultants, and the client’s environmental team. Noise management expertise across all these teams has significantly developed given the scope, range and duration of the work, and through development of a positive feedback loop, encouraged through development of a best practice working environment and communication of lessons learnt. Through the award winning approach this work should provide a legacy for future projects, enabling reduced disturbance of residents and businesses and an improved image for construction.
How did CEEQUAL influence the project?
Crossrail’s Sustainability Strategy identifies 18 key sustainability performance indicators designed to address the sustainability elements with the greatest relevance, impact, risk and opportunity for improvement; including for example reducing energy consumption, resource use in construction and whole life costs, and increasing local workforce employment and social inclusion. The value of CEEQUAL in helping to keep focus on these areas of performance was identified by Crossrail early in the project and a commitment made to use this as an assessment methodology by utilising it from design through to construction. Whilst Crossrail’s Environmental Minimum Requirements (part of the Crossrail Act, 2008) set a high bar for environmental performance, the use of CEEQUAL ensured that aspects of performance that were not included in these key indicators were also considered throughout the process. This allowed for incremental improvements to be made in several areas of project performance (e.g. opportunities to introduce new public amenity features into the project, consideration of end of life, factory application of coatings, and materials for permanent works). The use of CEEQUAL also provided a good discipline in evidence collection which as assisted the overall contract closeout process.