Middleton 400kV GIS Substation
First of its kind compact layout GIS substation, pioneering the development of this format
Recognised highly sustainable project, cutting CO2 emissions by over 30%
Cost and time savings through innovative solutions
An innovative and sustainable solution, the 400kV compact Gas Insulated Switchgear (GIS) substation at Middleton was one of the first of its kind in the UK. It paved the way in the use of a mini GIS kit, meaning a smaller footprint and cost savings on the building, and pioneered the support and installation requirements that have since been used on other compact GIS projects.
BakerHicks provided a comprehensive civil and structural consultancy service for the project, including:
In-depth geotechnical and structural analysis
Enabling works to raise the site level
Architectural detailing for the GIS building
Design and detailing for the steel frame GIS building and associated annex control and relay rooms, access road, perimeter security fencing, building services and the piled and ground bearing foundations for the overhead line-landing gantries, cable sealing ends, AIS/GIB equipment and external switchhouse buildings
Located on a greenfield site, with vehicle access provided along a disused railway embankment and connected to the existing road by a roundabout spur, there were a number of geotechnical and drainage issues to take into account in the design. The team raised the site level to eliminate the flood risk through a mechanically stabilised layer.
They ensured the top level of the weak organic clay and peat soil was not stripped, this mitigated long term settlements and saved both time and costs. The flood hazard presented by a perimeter ditch was eliminated by installing a buried filter drain in its place, ensuring the personnel and plant constructing the overhead towers could do so safely.
A highly sustainable design, the project was a finalist in the 2015 Construction News Specialists Awards Sustainability category. No excavated material was sent to landfill, with the equivalent of 7,420 tons being reused. A further of 5.1 tons of reinforcement and 430 tons of concrete were made through our highly optimised designs. In addition, by redesigning the cement design mix to incorporate a higher level of ground granulated blast furnace slag (GGBS), a 30% plus CO2 saving on all concrete structures was made. This also enabled cost savings to be made.
The new, more sustainable 66-80% design mix also replaced Morgan Sindall’s standard mix design of 36-65% for future projects, delivering continued environmental benefits across National Grid projects. Using a socket foundation on the perimeter fence rather than the usual substantial concrete foundation made further CO2 savings, with the fence beams used as anti-burrow measures rather than concrete beams. This removed the need for concrete and reduced the CO2 emissions as a result.
We also introduced the client to more sustainable systems, including Hybrid power generation and the ePOD plant management system, which further reduced CO2 emissions and fuel usage and gave the client a new, more sustainable methodology to take forwards to future projects.
The project was completed on time, with the civils elements being completed ahead of the baseline programme and with an excellent safety record.