Contractor Odebrecht has just completed the twin 5.87m diameter TBM tunnels for the Caracas Metro Line 4 project in Venezuela.

Using a Herrenknecht TBM, the Line 4 JV comprising CBPO de Venezuela (15%) and Constructora Norberto Odebrecht (85%), both of whom are Odebrecht subsidiaries, excavated two 3,666m long tunnels. The EPB machine was used to install a pre-cast concrete segmental lining of 5.16m id comprising six segments plus a key. The lining thickness was 0.2m, with each ring having a length of 1.4m.

As it runs parallel to the existing Line 1 in the Caracas valley to supplement its rider capacity, the Line 4 route crosses very heterogeneous soils; all kinds of sediments; colluvion and alluvion; sandy, silty and clay soils and even intersects shale and the rock basement. The entire line lies below the water table.

Danilo Abdanur, construction manager for Odebrecht, told T&TI that with a final predicted cost of US$323M, as at April this year, the Line 4 project had cost US$224M. The tunnel component of the total cost amounts to US$84M. Financing is arranged through BNDES, a Brazilian bank, (US$100M); CAF, development bank for the Andes countries, (US$70M); and the Venezuelan state, US$153M.

Following tender award in late 1999, the project got underway in 2000. Tunnelling started in January 2002 and was completed in April this year with the completion of the bored tunnels. Abdanur told T&TI that the scope also included NATM tunnels, stations and cut and cover structures. He said that general progress now stood at 84% with 7,332m of bored tunnel completed and 926m of NATM tunnel excavated and casting of the lining underway.

The volatile political situation in Venezuela had at times affected the project area with protest and riots in Caracas centre said Abdanur, but the more typical tunneling complications presented a greater challenge. Over 9km of services had to be diverted and 289 buildings had to be monitored and of these, 17 required foundation work to be carried out. T&TI was told that cutting tool consumption was very high, tool changes frequently took place, each time necessitating an intervention under compressed air. In total, 1,290 individual compressed air exposures occurred on the project.

Work is ongoing for the remaining stations that require concrete works, but the project is predicted to be completed by June 2006.