Millerhill Energy from Waste

Careys was engaged as a specialist subcontractor to construct a new mechanical treatment plant and 14MW Energy from Waste (EfW) facility, designed to process approximately 155,000 tonnes of waste per annum. The facility is owned and operated by FCC Environmental, a joint venture between the City of Edinburgh Council and Midlothian Council. The project won the prestigious Gold RoSPA Health and Safety Achievement Award for excellent health and safety standards.

Our scope included earthworks, concrete works, installation of foul and storm drainage, service ducts, earthing and lighting protection, infrastructure works and structural steelwork for the substation. It was our responsibility to construct Millerhill’s vast waste bunker and its waste chutes, as well as all of the associated foundation slabs for the main building. We were also tasked with installing the external concrete slabs and the hard landscaping.

The project was located on a former railway marshalling yard, which meant that in order to start the works we needed to divert and replace a Network Rail drainage culvert. When constructing the new waste bunker, we had to carry out extensive excavation works at depths of 10m. We ensured that zero utility strikes occurred during these works through providing extensive ‘safe digging’ training for all groundworkers and supervisors.

9000m3 of muck-away from the excavation works was produced on this project, and so presented a number of logistical challenges. At the peak of excavation works there were multiple muck-away wagons of over 100 per day to and from the site. To ensure that we did not disrupt the locality we built an independent access road with a wheel wash. A 40-tonne excavator from Careys plant and fleet was used to complete the deep excavation to formation level of the waste bunker.

Careys in-house design team checked the stability of the bunker prior to the slipform works commencing, and confirmed that no additional propping would be necessary to ensure the temporary stability of the structure throughout the slipforming.

However, temporary works were required at each opening for the seven chutes; doka props with scaffolding bracing were placed 1m apart and provided sufficient support to each opening until the full strength of the concrete was reached. Getting the props into position whilst the slipform was moving was a challenge - the slipform was rising (on average) 170mm in height every hour. We negated this through planning our operations thoroughly, and always ensuring that we had the correct number of operatives working each shift to complete each activity.

We trialled a number of different concrete mixes before starting the concrete works to ensure that the correct mix was secured. The most important thing was ensuring the setting times were accurate as the slipform operation was continuously running 24 hours a day for 18 days. The works were carried out in two shifts with a thorough handover done at each change of shift. Managing the concrete, including checking the quality of the concrete, and all other engineering and construction checks were carried out throughout the pour by the site team. Concrete technicians were on site constantly to carry out all of the concrete testing.

Capitalising on extensive slipform experience, the large, high-profile slipform solution was safely and efficiently designed and delivered in close consultation with the client team and stakeholders, in parallel to Careys’ robust in-house HSSQ and engineering-related procedures.

Careys engaged sub-contract partner UK Slipform to supply plant, equipment and specialist labour to build, install and operate the rig; this was supported by our own labour for the carpentry, concreting and engineering aspects. Working closely with UK Slipform, the team engaged with the design as early in the process as possible in order to incorporate lessons learned and to mitigate potential issues. The team ensured that the rig build and rate of rise targets were realistic and achievable, meeting the client’s time and quality expectations.

The slip required extensive cranage and concrete pump resources; early stage procurement was essentially paramount to ensure the programme was both met and maintained, without interruption to service. Similarly, sufficient concrete supplies were sourced to meet the high volume requirements of the rig; this included a system of contingency supply.

Proactive engagement with the various stakeholders ensured timely warnings of the 24 hour nature of operations.