Innovation
In order to reduce the construction footprint in both hazardous and contaminated ground, a value engineering proposal was agreed with the consultant and the client. The proposal included moving the shafts 2 & 3 originally located in contaminated fill to Shafts 1A & 5A, in doing so separating tie-in shafts from reception shafts, greatly reducing the overall schedule.
Tunnelling was reduced to 2 No. drives, the first drive containing 2 horizontal curves with a radius of 1640ft(500m) and 900ft(275m) and being 2400LF (732m) in length. The second contained a vertical curve of 910LF (278m). The vertical curve was included to avoid and existing culvert on the alignment which reduced the depth required for the reception shaft and provided further cost savings for the client.
During the construction of Shaft 1A, highly hazardous material was encountered which resulted in the drive length being increased by a further 322ft (98m) to the revised location of Shaft 1, situated in non-hazardous native ground. This was done to avoid encountering any further highly hazardous material. The radius of the second curve was reduced to 754ft (220m) to allow the tunnel alignment mine through Shaft 1A (Changed from a reception shaft to an intermediate shaft), through the existing 66” Brick sewer (Filled with grout from the surface to allow the MTBM safely mine through) and be received into Shaft 1, a total drive length of 2722LF (830m).
