TBM Begins Boring Sierra de La Cabrera on Madrid-Valencia High Speed LineTBM excavation of the longest tunnel has commenced on the future 914 km Madrid-Castilla La Mancha-Valencia-Murcia high speed rail link. It is a tunnel situated at Sierra de La Cabrera, of 7,246 metres in length, on the Siete Aguas-Buñol section, in Valencia province.The total bored length - both conventional method and TBM - is 2 x 7,137 metres. The length in cut-and-cover tunnel is 2 x 109 metres. The cross section of each bore is 53 square metres. The inner radius imposed by railway and aerodynamic factors is 4.375 metres. It is a twin bore tunnel, with an inner diameter of 8.75 metres each. Cross passages will be built each 400 metres between the two tubes. These crosscuts will be built simultaneously with the construction of the tunnels.Excavation of the tunnel by means of a tunnel boring machine has started at the exit portal on the Valencia side in Rambla del Gallo, at the closest end to Buñol, where the TBM has been assembled. The machine will be doing the bulk of the civil works, already begun in a previous phase by conventional methods in both tunnel tubes, i.e. 500 metres in the left tunnel and 250 metres in the right tube.The La Cabrera tunnel is located on the Siete Aguas-Buñol section. This 11.2 km section passes through a mountainous terrain crossed by numerous ravines, that greatly determines the alignment and obliges to build, besides the mentioned La Cabrera tunnel, two other tunnels in Siete Aguas (424 m in length) and Buñol (1,856 metres), as well as two viaducts. The length of the three tunnels totals 9,527 metres, which is 85% of the entire alignment of the rail section.The EUR322.3 million construction contract has been awarded to a joint venture of FCC and Construcciones Sando. The time frame to complete the job is 41 months. To date, 20% is completed. Visit www.fcc.es and www.sando.net TBM characteristicsThe machine is a hard rock double shield TBM produced by Herrenknecht (machine S-373) and assembled at the tunnel's east portal. It has a length of 200 metres and a weight of 2,400 tonnes. The shield diameter is 9,690 millimetres. The machine has a thrust capacity of 8,500 tonnes in total. The cutter head has a rotation power of 4,900 kW supplied by 14 electrical engines of 350 kW each and variable frequency drives. It is powered by a 20,000 V electricity supply, with two 700 V transformers for the engines of the cutter head and a 400 V transformer for the ancillary equipment. The main thrust force is 64,100 kN at 350 bar and the auxiliary thrust force is 85.000 kN at 350 bar. Visit www.herrenknecht.comThe tunnel will be excavated in carbonated rocky materials (limestone, dolomites, marly limestone, etc.). The machine is equipped with a ground exploration system ahead of the face to find out the geological conditions to be encountered while tunnelling, which enables the system and crews to adapt easier to the geological changes that may appear.The path of the TBM is controlled by a topographical and data processing guidance device that allows the exact excavation and control of the advance cycles from the control cabin. The integrated topographical device is capable to calculate the theoretical advance direction and the possible deviations that may occur. Visit www.vmt-gmbh.deThe average advance speed is 1.60 metres every 20 minutes. The advance is made possible by hydraulic cylinders propped up against the last installed segmental ring and pushing the shield forward as they extend so that the next ring of inner lining can be placed as the TBM progresses under the shelter of the shield tail. The machine is capable of placing the ring of seven precast reinforced concrete segments, each 8.5 tonnes of weight, that are assembled by connectors and screws. The segments have radial and axial gaskets to make the tunnel waterproof. Logistics As the rock is excavated, it is also possible to lay tracks behind the machine. The back-up or follower train is formed by 13 gantries towed by the double shield and two exclusive tracks are laid to allow access for supply and personnel transport trains. The control cabin, thrust system, grout to fill the gap around the outer diameter of the segmental rings and other components like cooling system, muck chamber, track storage, generators and pumps, conveyor belt, ventilation pipes, etc. are located within the back-up. It also includes safety facilities like a nursery and two pressurized chambers for emergency situations capable to bear high temperatures, with capacity for 20 people each, and air inlet from outside. Twenty-four people work non-stop in shifts inside the TBM. Engineering to protect the environmentThe La Cabrera tunnel has been designed and its construction planned to cause the smallest impact on the environment. Due to natural factors, the construction project takes into account the existing environmental corridors. Construction schedules have been adapted to the periods of bird nidification and the construction techniques have been exclusively thought to minimize impacts. The planned track level in the basic project has been modified in favour of a unique tunnel to avoid the construction of a viaduct on the Monedi ravine. Read E-News Weekly 8/2007. Click es/95. Visit www.adif.es 31/07.