Bespoke Ventilation System Ensures Fresh Air During Shaft Construction

Project Overview

Most of London’s sewage system dates back to the nineteenth century when, with typical foresight, the Victorians built it to handle the waste from a city twice as big as London then was. These days, though, London has grown to four times the size, and the system often cannot cope with the amounts of waste being produced. As a result, large amounts of untreated sewage frequently end up in the River Thames.

Tideway is a consortium of several construction groups set up specifically to deliver a new, upgraded sewage system for London. At the heart of the system will be the 25km Thames Tideway tunnel, which will reduce the amount of sewage waste entering the River Thames by 95 per cent.

Work on the tunnel will be carried out at 24 separate sites across London. Carnwath Road Riverside is the main site for the development of the western section of the tunnel. During excavation of the vertical shaft from which the TBM (tunnel boring machine) will be launched, it was vital to maintain good air quality within the shaft as it got deeper. RVT was asked to provide a safe ventilation solution.

Challenge

Working in a shaft is extremely high risk; Thames Tideway required a ventilation solution that would provide good quality air for the workers, especially as a diesel plant was also operating in the shaft.

Solution

The entire shaft construction took place within a 23m high acoustic ‘head house’, minimising noise and light pollution. Taking into account the diesel plant operating inside the shaft, personnel working within the shaft, and possible gasses that could be present both in the ground and the total area of the shaft, the following system was designed:

• Two Ventex 800CF units, each providing 50,400m³/h of airflow
  
• With the fans to be positioned inside the head house, intake ducting was fitted to ensure fresh air was drawn in and to prevent stale air from being recirculated
  
• Rigid 800mm ducting to be run down the side of the shaft, and for this to be extended as the dig progressed
  
• 800mm flexible ducting to be added to the bottom of the rigid ducting to direct the airflow to follow the tunnelling works, as Tideway constructed the launch tunnels for the main Tunnel Boring Machine
  
• RVT fans to be fitted with attenuators to reduce their impact on overall noise levels both inside and outside the shaft
  
• Manual extraction of dust and fumes to be provided to the entire area, given that the shaft head was enclosed, to prevent hazards building up inside

The shaft has since reached its final depth, ready for the TBM to be lowered down it and begin tunnelling. By tradition, TBMs are given female names, in this instance ‘Rachel’ after Rachel Parsons, an engineer and advocate for women’s employment rights, who set up a women-only engineering company, Atalanta Ltd, after the First World War.

“We called in RVT Group to ensure we are protecting the health and wellbeing of the personnel working down the shaft. Given the challenging spatial restraints, RVT Group provided the best possible solution. We are very pleased with the service provided.” - Phillip Neech, Site Manager