Project outline

Construction of a new 6.5km pipeline began in summer 2019 and is planned to finish by spring 2023. It will connect Bristol’s existing trunk sewer in Lawrence Weston to the Frome Valley relief sewer near Cribbs Causeway and will direct waste more efficiently around North Bristol to our water recycling centre in Avonmouth. 

The majority of the sewer has been constructed by tunnelling underground using a tunnel boring machine (TBM), reducing the need to dig trenches. Tunnelling will take place underneath key landmarks, including the M5 motorway and Network Rail’s Henbury Loop freight railway.

Key challenges

• Provision of 38,000 metres cubed of additional sewer storage capacity for North Bristol, which will allow significant growth in the area.
• Link the new relief sewer to two existing trunk sewers using live connection methods.
• Excavate open cut and tunnel through challenging, previously unknown ground conditions.

Project delivery and innovations

• Circular ‘Wier Walls’ reducing shaft footprint
• Vertform manhole shutters (see below)
• Mobilising storage using bespoke tunnel alignment
• Great Crested Newt Dog (see more below)

Key facts

• Construction of new 6.5km pipeline connecting Bristol’s existing trunk sewer in Lawrence Weston to the Frome Valley.
• We achieved 99.8% waste diverted from landfill. Materials used were from either re-cycled and/or sustainable sources wherever possible.
• The site achieved an overall rating of 'exceptional' from the Considerate Constructors Scheme.
• £55million investment, one of the latest largest sewerage projects undertaken by Wessex Water
• The Tunnel Boring Machine (TBM) used is named Fionnuala, she is the most powerful TBM in her class, RME131SE series 19900. The two front sections weigh 86 tonnes and are 65 metres in length when fully built.

Vertform manhole shutters

The Vertform manhole shuttering system is being successfully used on the North Bristol Relief Sewer Project in 2020. There were 6 large diameter manholes to be constructed on a DN1800 and DN1200 sewer. In addition there are a further 6 small diameter manholes to be constructed on a DN450 and DN600 sewer. The Vertform system offers a big advantage over traditional methods in the construction of manhole chambers. The system consists of a range of fibre glass panels which can be arranged to form a channel without the need to bench the manhole afterwards. The manhole base is constructed in one continuous concrete pour. The system caters for a range of pipe diameters from 300mm up to 1800mm. In addition various panels are provided which can accommodate a range of inlet and outlet pipe angles.

Great Crested Newt ‘Detection Dog’

The Wessex Water region is a stronghold for ‘great crested newts’ and therefore of particular concern during the sewer’s construction. An amazing and innovative solution has been introduced into locating these protected creatures - ‘Freya’ the ‘Newt Detection Dog’. Wessex Water are the first utility company in the UK to have an in-house great crested newt detection dog, owned and trained by ecologist Nikki Glover.

If construction works are within 250 metres of breeding ponds and we are likely to cause an offence under the legislation, we must apply for a licence from Natural England. We would then be required to fence off the construction area and carry out pitfall trapping (buckets sunk into the ground), which could take around 30 days to complete.

Nikki and Freya will be working alongside the team from Murphy during the construction of the new sewer as an additional tool alongside current mitigation measures.