On 9 September, the breakthrough took place for the 11.9m diameter NFM Technologies dual mode hard rock TBM on Section IVa of Barcelona metro’s Line 9 project in Spain (T&TI, February, p26).
The Linea 9 JV comprising FCC / Ferrovial-Agroman / OHL / Copcosa y Copisa, won the Section IVa contract from UTE Linea 9 for 4.3km of 10.9m i.d. tunnel driven at depths of 15m-90m through igneous and metamorphic rocks, which vary from fresh to weathered granites to pelitic hornfels. As it has bored through these conditions, the TBM has erected a 350mm thick fibre reinforced concrete segmental lining consisting of eight segments plus a key.
The NFM machine is operable in open mode using belts for muck transport and closed mode using screw conveyors to extract muck from the cutting chamber. Since its launch in June 2003 from Can Zam station, the machine has encountered heterogeneous geology along the 4.2km route to its reception shaft roughly 600m past Can Peixauet station and has operated in both closed and open modes. T&TI was told by NFM that the first 2.4km was driven in open mode, followed by a 150m long section in closed mode, then approximately 1km in open mode and the final section in closed mode.
Early challenges faced by the site team were related to segment stabilisation behind the shield that was eventually resolved by adjusting the components in the backfill grout. Also, over-excavation ahead of the face was a problem, it is thought due to the large TBM diameter and rock fracturing resulting in decompression of the face. This was overcome by closing up the cutting wheel to prevent oversize blocks falling through the cutterhead openings.
NFM said the machine is now to be dismantled and transported to the launch pit to bore the 9.5km long Section III to Sagrera Station. A project source told T&TI that NFM has manufactured a new cutting wheel for the section that includes 1.4km of soft soil..
