Work at Avonmouth
In March 2019, we started construction activity at Avonmouth to modify the substation and replace a section of overhead lines going north, out of the substation, with underground cable.
This work is clearing the way for the construction of the new connection being built between Bridgwater and Seabank Power Station.
As part of this project, we’re working with Western Power Distribution (WPD) to make significant changes to their local electricity network by removing 67km of their existing overhead line and pylons.
As WPD own and maintain the local electricity distribution network, the work at Avonmouth is being completed by WPD and its contractor, Balfour Beatty.
We recognise this work may affect local businesses and we’re continuing to make every effort to minimise disruption and inconvenience. We notified local businesses before starting this work and we’re continuing to keep them updated on any activity that’s likely to cause any inconvenience.
Access and traffic management
The project vehicles travel to the construction area from the M5/M49 at Junction 18A and onwards along Avonmouth Way.
A temporary traffic access point has been created off the lower end of Avonmouth Way to connect to a temporary haul road installed along the route of the underground cable. The haul road allows us to move traffic away from the Avonmouth Way directly into our construction area, limiting our use of the local road network.
To view a map showing the temporary traffic access point and haul road, please click here.
For our contractors to work safely and efficiently with as little disruption to businesses as possible, the traffic management includes:
- A ‘No waiting’ restriction along a section of Avonmouth Way
- A temporary speed limit reduction on Kings Weston Lane
- Traffic lights on Kings Weston Lane that work on a sensor and stay on green for local road users, only changing to red when project vehicles need to safely cross the haul road. They will remain in operation until we’ve completed work in this area.
Temporary construction compound
The construction compound for this work is just off Kings Weston Lane. It includes offices and areas for storing construction equipment and materials, as well as parking and staff welfare facilities.
The construction compound, traffic access points and haul road are temporary. They will be used for WPD’s work and for future overhead line construction work, which is planned later in the programme. They will be removed when all our work in this area is complete.
The substation on Avonmouth Way is owned and maintained by WPD.
To join the new underground cables to the electricity network, WPD is carrying out minor modifications within the substation by installing three new cable sealing end (CSE) structures. These consist of low-level metal supports, erected on small concrete pads.
This work is being completed within the existing boundary of the substation.
Underground cable construction
The underground cable is being installed along a mixture of open land, under roads including Kings Weston Lane and Lawrence Weston Road in the direction of the raised section of the M5/M49 at Junction 18A.
We’re installing six underground cables within two trenches (three cables per trench). Each cable trench is approximately 1m wide by 1.3m deep. We’ll then install ducts that will enable us to close each section of trench promptly. This technique helps to protect the soil structure of the land, minimise impacts on wildlife and the environment and is much safer for our staff than leaving trenches open for long periods of time.
To reduce the construction timescale along Avonmouth Way, we’re installing the underground cable in existing ducts that have spare capacity. Where the underground cable crosses Kings Weston Lane, the ducts have been constructed using a horizontal directional drill (HDD).
When ducts have been installed along the length of the cable route, we’ll start to install the cables.
At intervals along the route, sections of the cables will be joined together in joint bays.
After the cables are fully installed, they will be tested and commissioned.
To join the new underground cable to the network, we need to build a new CSE pylon.
Cable sealing end pylon
The CSE pylon will be in a field next to the M49, near the railway line over the M49, 100 metres away from the overhead line being removed.
Temporary scaffolding and fencing will be required around its base to create a safe working area.
During 2020, we’ll remove the existing overhead line, which runs north of Avonmouth substation to the existing pylon next to the M49.
We’ll remove the wires from this overhead line before removing the pylons. The wires will be lowered to the ground, cut into smaller sections and collected for recycling.
The existing pylons will be taken down by crane, either piece by piece, or by cutting two of the four legs and slowly lowering each pylon to the ground on its side, before it is cut into pieces and removed.
To remove the wires that over sail the M49, temporary overnight closures will be necessary. The overnight closures will be managed with the agreement of Highways England. Information signs will be in place to provide road users with advance notification of the temporary closures.
Our agreed standard working hours are between 7am and 7pm Monday to Friday and 8am to 5pm on weekends.
Most work is carried out on weekdays, although there may be occasions when we need to work at weekends or outside the standard hours. These may include when we are working on a continuous process such as cable joining, if adverse weather or ground conditions cause delays, or to avoid traffic delays during the week, but there are restrictions to this.
National Grid is committed to protecting the natural environment and we recognise the potential impacts our construction work may have.
To reduce and mitigate these impacts, we have carried out extensive surveys and have discussed the best ways to carry out the work with specialists from Natural England, Historic England, local authorities and many others.
Pre-construction activity includes implementing schemes to reduce disruption to wildlife and animals. These include managing and strimming vegetation to prevent birds and water voles nesting in areas where we’ll be working.
Once all the work is complete, the land will be reinstated and returned to its original use with trees and hedgerows replaced at a ratio of 4 to 1. Wherever possible, we’ll replant in the same location. Where this is not possible, we’ll plant at an agreed location nearby.
To help reduce the overall impact of the new connection and enhance local landscape and biodiversity, we’re running a scheme for landowners to host additional native tree and hedgerow planting.
We value and welcome your interest in the project. Please visit our contact us page and get in touch.
Select points on the timeline below for details of what is happening at each stage of work.
Pre-condition surveys and managing and strimming vegetation
Preparing for start of construction activities; installing drainage, setting up construction compound and building traffic access points and haul road
Digging trenches and laying cable ducts, installing cables and preparing joint bays, setting up and preparing site to build the new cable sealing end (CSE) pylon
Modifications within Avonmouth substation
Installing cables, cable jointing and building new CSE pylon
Cable testing and commissioning
Removing the existing overhead line before removing the haul road and reinstating and landscaping the area we’ve been working in. Expect to complete during autumn 2020.