Oberosler and Edilmac move to hydropower project

Following successful work for the contractor Oberosler on the Laives Tunnel in Bolzano, Italy, in 2011, the specialist raiseboring team of Edilmac commenced another project for the same contractor on the Mulbach Rio Pusteria hydropower scheme, also in Bolzano, South Tyrol.

Work involves two 431m-deep, vertical penstock shafts, one 1.84m in diameter and the other 1.55m. The RVDS (Rotary Vertical Drilling System) will be used for the pilot hole through granite before reaming. The automatic RVDS has been developed by Germany-based Micon Mining & Construction Products with current tool diameters of 9.5 in. (241 mm) to 12.875 in. (327 mm).

On the Laives Tunnel, Edilmac and Oberosler were partners in the Laives Tunnel consortium together with Wipptaler, Rottensteiner, Gasser, Klapfer, PAC and Fondazioni Speciali. The consortium has been building a new road tunnel for the Province of Bolzano on the SS12 route. Here Edilmac sank a vertical ventilation shaft 280m deep and 4.74m in diameter. The geological conditions were difficult, including porphyry formation.

Edilmac’s logistics involving another nearby site meant that two sets of equipment were used on the shaft. First the pilot hole was bored using Edilmac’s Atlas Copco Robbins 83, and then reamed to its full diameter using a Herrenknecht 550VF. On completion of the excavation the shaft was lined from a platform supported from a bridge crane over the shaft, which was also used to transport the materials and equipment. The gantry crane also carried a winch to lift operatives through the shaft.

The RVDS operates using steering produced by expandable stabiliser ribs with inclination monitoring using two accelerometers. The monitoring data so generated is handled with full digital, downhole, closed-loop control and transmission to the surface by mud pulse. The system is particularly accurate with an average deviation on all projects so far recorded of only 0.07 per cent. So far the systems have been used on 227 projects since introduction in 1993, with a total drilled length of 81.3 km.