A tight site and tricky ground conditions ensured that Morgan Sindall had to work closely with National Grid to build a new substation at Kensal Green.
- Dealing with Crossrail and conservationists
- Premium Paddington drives innovation
- Close crane demands collaboration
Morgan Sindall is building a new substation in west London as part of its alliance with ABB, working on behalf of National Grid.
The new substation at Kensal Green forms part of the wider £1bn London Power Tunnels scheme, which will provide new supplies and upgrade the high-voltage (275 kV and 400 kV) power transmission system across London, supporting the increase in demand for energy in the UK’s continually growing capital.
The Kensal Green substation is situated between the existing Willesden, St John’s Wood and Wimbledon National Grid substations, which will be linked by 20 km of 3 m and 4 m-diameter tunnels.
These tunnels will provide the conduit for the new electricity supplies into London.
The new substation also features two transformers that will deliver a 27.5 kV supply to the Crossrail project, which passes immediately next to the works.
Dealing with Crossrail and conservationists
The project included the construction of three steel-framed clad buildings and a brick-built building along with a substantial retaining wall, drainage, ducting, troughing and perimeter fence works.
Morgan Sindall’s work has involved liaising with National Grid in supporting the planning application submission, and co-ordinating with other parties such as Network Rail and the Canals and Rivers Trust as part of the construction process.
Ground works on the site involved dealing with considerable ground contamination, a legacy of gas works and industrial activity in the area.
“Ground works on the site involved dealing with considerable ground contamination, a legacy of gas works and industrial activity in the area”
Excavation of this material involved a significant amount of testing as works progressed to ensure the material was disposed of correctly.
Ground conditions also dictated the use of reinforced concrete piled foundations for the buildings and transformer bund.
These were installed using a rotary rig to minimise vibration given the proximity of the canal, railway and gas works.
Premium Paddington prompts innovation
The substation is wedged between the Grand Union Canal and National Rail lines forming the approaches to Paddington station.
Availability of land for industrial purposes such as this in London is at a premium.
This prompted a more innovative design, using compact gas insulated switchgear manufactured by ABB to allow the substation to have a very tight footprint, ensuring best value for National Grid and its customers.
Morgan Sindall has built two steel-framed buildings to house this switchgear and provide a dedicated control building.
“The combination of the tight footprint and multiple contractor interfaces required close collaborative engagement between all parties on site”
Both of these buildings (and two head houses constructed by others) are clad in a secondary architectural mesh.
This mesh is supported on an exoskeleton of steelwork fixed outside the normal weatherproof shell of the building.
Ground levels on site (an approximate 6 m difference between canal towpath and rail side) meant that a sizable retaining wall was required to maximise the footprint available for the substation construction.
Close crane demands collaboration
Due to the presence of an existing wall on a similar line, Morgan Sindall installed a temporary sheet pile wall prior to removing the existing concrete wall.
The new reinforced concrete retaining wall was then constructed using traditional panel shuttering moved in panels by mobile cranes.
Use of a crane close to the Network Rail line necessitated close collaboration with Network Rail, which had a safety representative on site during periods when the crane was in use.
The combination of the tight footprint and multiple contractor interfaces required detailed and extensive engagement between all parties on site.
This has been managed through regular co-ordination meetings with all parties working on and next to the construction site.
After two-and-a-half-years’ work, a major milestone was achieved on 21 July 2015 when the project achieved its High Voltage System Clearance Certificate, meaning the site was accepted by National Grid, and is now operational.
While the majority of work is complete, the remaining works will be finished in the first quarter of 2016 following the completion of third-party works on the site.
Ian Chappelow is contract manager at Morgan Sindall