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Well travelled TBM

TUNNELLING

Careful selection of equipment, including a refurbished tunnelling machine shipped from Australia, has meant Portuguese tunnelling through tough ground was finished on time.

Since 1985, the Funcho dam has provided most of the potable water requirements for Portugal's Algarve tourist region.

But as the popularity of the area has increased over the years, so has its demand for water. Now a new earth dam is being built at Odelouca, together with a water transfer tunnel to connect with the 3m diameter pipeline from the Funcho dam to the main treatment plant.

Tunnel boring was chosen for the 8km drive through sedimentary rock formations, using a 3m diameter refurbished Robbins machine.

Contractor Spie Batignolles, supported by Ramalho Rosa Cobetar and Etermar, brought the tunnel in on time, despite some unexpected geological conditions.

Little exploration drilling had been carried out along the route of the Odelouca-Funcho tunnel, so very limited information was available to the contractor. Most of the project was expected to be excavated in sandstone, with unconfined compressive strengths (UCS) between 40MPa and 100MPa, with some greywacke approaching 200MPa.

expected in just 2% of the overall length. The entry portal was in good quality sandstone, with strength close to 100MPa.

The cost structure of the project effectively ruled out buying a new tunnel boring machine.

However, the diameter and the geology were a reasonable match with the Mangrove Dam to Boomerang Creek project in Australia, which had been excavated by TBM during 1987-88.

This project comprised 11km of tunnel in sandstone with UCS between 30Mpa and 80MPa.

Fortunately, the TBM owner, Australian contractor Thiess, had stored the machine well, so there was little deterioration of major components, with only the electrics requiring complete renewal. The TBM was refurbished by Terratec, and supplied together with a backup system designed to integrate with the rail-bound muck removal method.

Spie Batignolles, which had recently completed a 9.8m diameter section of the Lisbon metro system using a soft ground TBM to install a full segmental lining, decided that the backup system should have sufficient length to accommodate muck wagons for two 1.2m strokes of the TBM.

Modification specifications were engineered by Terratec at its Tasmania office. The open gripper model was fully refurbished, and the cutterhead dressed with 24 cutters. Terratec used computer-controlled critical path analysis techniques to monitor the design, fabrication and procurement of the various facets of the TBM and backup production.

Electronic data transmission between the two parties contributed greatly, saving time and cost, the team says.

Design, erection and repairs beat the schedule of 19 weeks, and the 80t TBM was transported by ship and road fully assembled, also reducing delivery time. It arrived in Lisbon in February 2002.

A rail haulage fleet of four battery locomotives was bought especially for the project and track laid from a purpose-built surface dump to the tunnel portal, and into the TBM position. The 80m deep launch tunnel was driven using a hydraulic hammer with steel horseshoe arches and shotcrete for support.

TBM installation took just five weeks, and tunnelling began immediately afterwards. The general run of ground was folded, with schist. A total of 258m of fault area was encountered during the drive, where steel sets had to be erected, together with Atlas Copco Swellex bolts and shotcrete as required.

About 16,000, 1.8m long Swellex Mn12 rockbolts were used in the tunnel as primary support, generally in a pattern of two bolts spaced around the crown at 1.5m spacing, tightening to 1.2m spacing when ground conditions deteriorated.

Shotcreting was initially carried out using an Aliva 262 machine, but this was replaced with an Aliva 246 which was easier to use within the space available. The crown and side sections of the four-piece steel arches were set behind the cutterhead, and the invert section was closed after the trailing back-up had passed.

The TBM advanced an average of 27.5m a day, peaking at 96.8m in one day, and the best month's advance was 1,062m. Despite the difficult ground, cutter consumption was low, with each completing nearly 1km of drive before being sent to Italy for repair on a three-week turnaround.

The TBM was equipped with handheld drills for rockbolt installation, and a dust extractor to cope with the dry shotcrete. An Atlas Copco COP 1238 drifter with slide was mounted towards the front of the backup for probe drilling.

Tunnelling was completed in summer 2003 and the tunnel is now being lined with 2.4m diameter cast insitu concrete rings using three 24m long CIFA formworks.

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