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Thames Tideway Tunnel Inspection

Case study

120+ Years Experience Over 120 years' experience
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The Thames Tideway Tunnel, London's new "Super Sewer," is an ambitious infrastructure project designed to modernise the city's ageing sewage system. Stretching 25km beneath the River Thames, this £4.5bn state-of-the-art tunnel aims to significantly reduce sewage overflows into the river, improving water quality and environmental standards. 

There are 21 shafts constructed on the project used to divert sewage flows from London’s existing Victorian sewage network to the new 25km tunnel, which range in depth from 35-66 metres across the project. The internal diameter of the tunnel is 7.2m.

Scheduled for completion in 2025, the Thames Tideway Tunnel project will enhance the capacity of London's sewer network, supporting the city's growth and resilience for decades to come. This project represents a major step forward in safeguarding public health and maintaining the ecological integrity of one of the UK's most iconic rivers.

The Requirement

Removal of the bulkhead wall isolation between the Lee Tunnel and Thames Tideway Tunnel was required to create one single system, allowing flows to reach Beckton for treatment. 

Before commissioning and handing over to the contractors, a walk-through visual inspection of the Lee Tunnel needed to be completed, capturing video and photographic records. Due to the length of this part of the tunnel – 6.9km – the inspection was split into two halves. Personnel would enter the respective shafts on different days and travel to the halfway point. 

To gain entry, complex isolation procedures were required to prevent tunnel inundation, including a contingency flow diversion plan at Abbey Mills Combined Sewer Overflow and closure of the Tideway Pumping Station.

Our Approach

A detailed Risk Assessment and Method Statement (RAMS) was prepared by the MRS Industrial Rescue Experts and a comprehensive emergency rescue plan. A team of nine specialist Rescue team members were on hand to support the entry into the shafts and tunnel and provided:

  • Two MRS Rescue Workers (Safety Guardians) accompanied the inspection team. The MRS team were fully equipped with Drager BG4 long duration closed circuit breathing apparatus (uncoupled), due to the length of the tunnel, and travelled at the front of the inspection party. 
  • Two MRS team members (located at the shaft bottom) whose role was to communicate between the entry team and the team on the surface, again fully equipped with BG4 (uncoupled). 
  • An MRS Team Leader/BA Controller located on the surface with 4 MRS Rescue team members equipped with BG4. The rescue team members would be available for immediate deployment and would be on standby at the surface entry point.

A detailed communication plan was developed and during the inspection, we maintained communication between the entry team and rescue team at allotted timescales. We also equipped the inspection party with suitable environmental monitoring, chemical oxygen escape equipment, confined space rescue harnesses and communications equipment.

Air quality checks throughout the depth of the shaft were undertaken and recorded by the MRS Rescue Officer/ Entry Controller following a 48hr pre-ventilation period of the workings. These checksdemonstrated that the air quality was sufficient to allow entry without the requirement to be coupled up to Breathing Apparatus (BA). 

Entry was then permitted, and the MRS Survey/Inspection Team were lowered into the shaft via a Crane with a person-riding basket.

A workstation/Fresh Air Base (FAB) and air quality monitoring point was established at the bottom of the entry shaft with radio communication to the surface team.

During the inspection, The MRS team had full responsibility for ensuring the safety of the confined space - ensuring strict adherence to the control, management and monitoring of pre- determined permit, entry and Isolation arrangements. 

This included walking the line with the inspection team, carrying out ‘weir watch’ – monitoring river levels and pen stocks, ensuring levels are not rising to the risk of people – monitoring gas levels, air quality and overseeing the ventilation process and standards. 

The MRS Inspection Team was equipped with Dräger BG4 long duration closed circuit breathing apparatus. This was worn/carried but not coupled up and would only be used if required/deemed necessary via dynamic risk assessments during the inspection by the MRS Team Leader.

The Results

This inspection was part of a 2-week program that included a total of 129 separate isolation points spanning across London, from Acton in the west to Beckton in the east, using more than 270 padlocks! With an isolation this complex, there was a great deal of planning and focus needed to ensure safety remained the top priority.

This was one of, if not the biggest isolations the Thames Tideway Tunnel project has used, including cross boundary isolations, and the merging of different Safe Systems of Work across different contractors.

Whilst the bulkhead wall removal works were going on at Abbey Mills, there were two teams completing works at Beckton. 

The first team constructed a new weir wall on the Lee Tunnel network to ensure correct hydraulic operations of the newly connected system. We were part of the second team that conducted essential maintenance on roller gate penstocks located in a wet well at the 70 meters deep Lee Tunnel Connection Shaft, in addition to inspection of the Lee Tunnel. 

While working on an extremely tight schedule in adverse weather conditions, the teams still managed to get the work completed ahead of schedule. 

Going Forwards

In the coming weeks and months, the entire system will be carefully brought online with individual sewer interception points being connected to the new tunnel. The experience and lessons learnt from the inspection of the Lee Tunnel have set a precedent for future entries of the Tideway Tunnel for inspections and maintenance.  

The Mansfield MRS team provided confined space rescue cover for AtkinsRéalis during their inspection of the Lee Tunnel on behalf of Thames Water. This is one of London's deepest tunnels, with limited access points, and requiring a complex network of isolations to keep the tunnel safe from the live sewer network. The rescue team were exceptional in their professional capacity from start to finish and were highly commended by the inspection team and Thames Water for their procedures and conduct. They went above and beyond in collaborating with all parties to ensure works during the tunnel shutdown were carried out safely in a timely manner. Would highly recommend using MRS Training & Rescue.
Joe Dai, Tunnel Engineer
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