Following the poor ground encountered after its launch in August, Robbins said its 10m diameter TBM driving the Lot 4 west tunnel on Spain’s Pajares rail project is expected to move into better ground imminently.
Although such poor ground is not an ideal circumstance to showcase machine performance rates, the Robbins single shield was designed with measures to overcome poor conditions such as squeezing and blocky ground. The TBM was designed by Robbins and built by MHI-Duro Feguera in Spain. Robbins is also supplying the back-up system, electrical and hydraulic components, field service, shield engineering and part of the muck conveyor system.
The tunnel is part of Spain’s Alta Velocidad Española (AVE) highspeed rail link. Two 10.5km long parallel tunnels are being built along an east-west axis.
Robbins said that a section of “very fractured and blocky” rock was encountered after the TBM launch, but it was expected that better conditions would prevail after a further kilometre of drivage. The route alignment passes under topography giving a 1,000m overburden with a high potential for faults and squeezing ground, so the TBM was designed with this in mind. The geology consists of sandstone, shale, limestone, molasses and volcanic rocks of up to 90MPa UCS.
T&TI was told that the TBM has “several unique features to combat these difficult conditions.” It is equipped with an articulating cutterhead to overbore by 400mm so it can progress through highly pressured rock. In addition it has a mixed cutterhead to help cope with blocky conditions.
A 500mm thick precast concrete segmental lining is being installed concurrent with advance. Robbins has integrated the first section of conveyor into the back-up so as to reduce the number of transfer points between conveyors.
Space is saved in the tunnel as only a short transfer conveyor is utilised to link the back-up conveyor to the main tunnel belt. Maintenance time and the potential for breakdown is also said to be reduced compared to the more usual approach that has three conveyors in the back-up.
Project owner Administrador de Infraestructuras Ferroviarias (ADIF) awarded the Lot 4 west contract to a JV of Constructora Hispanica, Azvi, Brues y Fernandez and Copcisa.
The tunnels are part of the 49.5km long Pajares bypass to connect Asturias to the Madrid-Valladolid leg of the AVE highspeed network. By 2010 most provincial cities will be linked to Madrid and Barcelona by the network.
