TECHNICAL | BTS MEETING/NORTH BRISTOL RELIEF SEWER
● Early design engagement with the client was effective in optimising the design solution (alignment modifications and deletion of shafts).
● The use of a geostatistical 3D ground model and the award-winning ML programme that was developed on this project proved effective at estimating production rates through unproven ground conditions. Murphy is continuing to undertake R&D in this field and looks to take this further into future projects.
● Early engagement with the supply chain worked effectively through COVID-19 at minimising the impact.
● Murphy’s in-house capabilities all proved effective at supporting the project as and when the various needs arose and demonstrates the full breadth of Murphy’s capability.
● Murphy Applied Engineering, ● Murphy Plant Ltd, ● Murphy Ground Engineering, ● Murphy Electrical Services, ● Murphy Welding Services ● Murphy Pipeline Services, ● Whilst no single type of TBM would have been suited to all the ground conditions encountered, some spoil handling and grouting variations would have been beneficial when dealing with the challenging ground conditions. For example, a TBM that had the screw in the invert of the cutting chamber, and tailskin grouting may have improved the working conditions within certain elements of the tunnel drive length.
QUESTIONS AND ANSWERS
Q: During the design development how were the savings shared between the designer, contractor, and client? A: The design was refined at the end of the tender stage, which was then largely fixed going into the construction stage, so the savings went back to the client at the start of the project.
Q: How much site investigation information was available during bidding and how deficient did you find it? A: Murphy changed the tunnel alignment during the tender stage and what we found during the construction stage wasn’t necessarily what we had during the tender.
Q: What proportion of the tunnel spoil remained on site for the school and what did you do with the rest of it? A: We retained approximately 7,000m3
of the 50,000m3
from the tunnel on site and the remainder was disposed off-site into a local quarry that was being backfilled.
Q: Did the challenging ground conditions have an impact on the line, level, and circularity of the finished tunnels? A: No, the tunnel was constructed through stable rock, and we recorded no impact from the ground conditions on the line, level and circularity of the tunnel rings. Additional grout was injected to ensure that the annulus was filled no matter what the conditions, at times up to 3x the theoretical amount.
Q: If you had to do the same job again what changes on the TBM what you make and how do you think a slurry TBM would cope? A: TBM selection was debated in some detail and if we were to build it again then we would probably look at using
a slurry machine with enough power for the conglomerate, however, no single type of machine was suitable for all the ground conditions encountered along the tunnel drive.
Q: If you had to do the same job again what changes on the TBM what you make and how do you think a slurry TBM would cope? A: TBM selection was debated in some detail and if we were to build it again then we would probably look at using a slurry machine with enough power for the conglomerate.
Q: Was biodiversity lost due to the expanded site footprint considered with regard to the new legislation coming into effect for a biodiversity net gain of 10 for all projects? A: Scoring wasn’t undertaken on this project.
Q: Was there a reason you didn’t go for tailskin grouting at the start of the project? A: The way the TBM was configured is without tailskin grouting and with this particular TBM we have successfully grouted through the rings on previous projects.
Q: Was there any consideration about a secondary liner, GRP or similar for the tunnel to protect from hydrogen sulphide and increase its life expectancy? A: The design life is 100 years for this tunnel, and we did investigate the options of a secondary lining with Wessex Water during the tender stage and it was deemed they didn’t want one. The lining itself is fully pointed and grouted but no allowance for a secondary lining within the design.
Q: How often were you changing cutter tools? A: 700m centres in the mudstone, 70m in the conglomerate, and 15m in the sandstone.
26 | November 2023
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49
