The debut drive of Seli’s new compact DSU TBM system (shield, back-up and transport), which is intended to be an alternative to general use of open shields and where concrete segmental lining is not used, is getting underway at the Crevola Toce III hydropower project in Italy.
Seli aims for the system to make TBM use more competitive with heading and bench excavation in shorter bores. At Crevola Toce III, though, the 4.2m diameter shield is to drive 8,589m, or 94%, of the tunnel for the project being developed by energy utility Enel.
The manufacturer is supplying another, 4.5m diameter compact DSU to the Dragados-Besalco JV for the 8,125m long mine bore on the Los Bronces project, in Chile.
Seli said the compact DSU system is designed to give double shield advantages but be shorter, simpler and more easy to operate, and it is bolted for dismantling. The integrated package should also give production and safety advantages and cope with all ground conditions, it added.
The TBM has three operational modes – gripper in either stable or unstable rock, and single shield in fault zones, which should be helped by the short length of the machine. It has a probe drill mounting and also roof drills for rock bolts.
In terms of lining, the system works with typical NATM systems but where segmental lining is warranted it has ring erector for steel but does not handle precast concrete. Back-up is typically 50m-65m and include a double capacity dust scrubber for machines of that size.
At Crevola Toce III, geology along the alignment consists of gneiss, mica schists, marbles, lime schists and dolomitic sediments. The shield (DS-0420-121) has cutter discs of 19” diameter and rotational speed of up to 11rev/min. Tunnel lining will comprise steel ribs, shotcrete, rock bolts and lining plates.
Construction of the headrace tunnel will also include an intermediate stretch approximately 540m long about 6,150m into the drive from the outlet portal. The TBM is to be dismantled and reassembled at the inlet portal to drive in the opposite direction while the weaker zone is opened by drill and blast.
The contractor for tunnelling is a Seli-led joint venture with Monti and Giacomini. The contract was awarded last year with a value of Euro35.5M (US$50.1M in October 2007, now US$45.8M) for the excavation and other works, and is due for completion in late 2010.
Seli has developed a new compact DSU system, the first use of which is on the Crevola Toce III project, Italy Seli’s new compact DSU system
