BTS MEETING/NORTH BRISTOL RELIEF SEWER | TECHNICAL
Left, figure 8: TBM drive site overview
right at the start of the tunnelling phase and caused the works to be delayed by three months whilst the SSOWs were produced, and the project was able to procure enough PPE/RPE in accordance with the SSOWs to safely commence tunnelling within a small diameter tunnel. The project’s approach to managing the risk of COVID
was to zone the worksite and tunnel (including the TBM).
There were three zones created: ● Green zones, which meant no additional PPE or RPE was required and that the 2m social distancing could always be maintained.
● Amber zones, where operatives were required to always be equipped with additional PPE/ RPE but would only be required to put it on when the 2m social distancing could not be maintained.
● Red zones, where it was not possible to keep the 2m social distancing at any time and therefore additional RPE/PPE had to be worn (for example, in the passenger cart of the rolling stock).
In addition to the zoning control, the project were
early adopters of a testing regime when the testing kits first became available. Initially, testing was completed daily to identify any cases early and then isolate those associated individuals/teams. As the guidance began to relax testing was reduced to 3 times/week, where it stayed in place for the duration of the tunnel drive.
Production rates The table summarises the tunnel production rates and the impact of the challenging ground conditions.
CIVILS CONSTRUCTION MH01 and MH12 To construct the upstream (MH12) and downstream (MH01) connections into the existing sewer, two large reinforced concrete chambers were built. These were constructed within large temporary sheet piled pits established around the existing live sewers. The reinforced concrete chamber was then fully built around the connection points, which required a series of bespoke temporary works that were provided by MAE.
Table 1: Tunnel production rates and the impact of the challenging ground conditions Tunnel Section Average per week Length (m) MH07 – MH09 MH09 – MH10 MH10 – MH12 Total
60m 67m
122m 67m
2030 1200 2200 5430
Comment
Including the learning curve and the worst of the ground conditions Ground conditions started to improve halfway through this section As expected, ground conditions Long average
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