The two Lovat TBMs driving a second pair of water transfer tunnels in Algeria have holed through to complete a total of 10km of excavation.
Tunnelling subcontractor SNC-Lavalin bored all four tunnels on the water transfer scheme for main contractor Cooperativa Muratori & Cementisti di Ravenna (CMC), working for over a year from February 2006.
Geology along the alignments consisted of marl, which varied from hard and compacted to very compact with UCS up to 70MPa. The depth of cover was a maximum of 95m and the drives were entirely above the watertable.
The 3.7m diameter Lovat hard rock TBMs – ‘Isabella’ and ‘Susanna’ – were built with pressure relief gates for face isolation. The cutterheads have 524kW hydraulic drives and operate from 2.5rpm-9.5rpm.
‘Isabella’ began excavating the 2667m bore of the Naciria tunnel last September and completed the drive in five months. Monthly production reached 490 expanded rings when placing 2197 rings in total over the drive.
Each ring in the primary lining comprises three segments plus an invert base. The secondary lining consists of grouted-in-place concrete pipe.
SNC-Lavalin had previously driven the RMP146E, Series 22000 TBM for the 2800m drive for the Tizi Ouzou tunnel in less than 24 weeks to hole through early August.
The second, twin TBM – ‘Susanna’ – also completed its final drive in February after driving 3298m for the Thenia tunnel. Best monthly production was 515 rings and a total of 2745 rings were erected.
‘Susanna’, a Series 22100 TBM, previously excavated the Draa-Ben-Khedda tunnel from March to May last year. The drive was 1200m long.
