An important construction milestone has been achieved at the Snowy 2.0 project in Australia, with the successful completion of a second tunnel excavation at Lobs Hole.
The completion of the 2.93km emergency, cable, and ventilation tunnel (ECVT) marks a significant step forward in the project's progress. The tunnel was excavated and lined with 13,140 locally-manufactured concrete segment by tunnel boring machine (TBM) Kirsten. This achievement follows the earlier completion of the adjacent main access tunnel (MAT) in October 2022.
Snowy Hydro CEO Dennis Barnes said solid progress was being made at the project, with around six kilometres of tunnelling by TBMs completed and drill and blast excavation of the power station cavern about to start.
“We are extremely pleased the ECVT excavation has been completed and the whole project team is excited to be moving into the next critical phase of construction. Our huge power station cavern will be located about 800 metres underground and will be one of the largest and deepest in the world,” he said. “We are also using drill and blast methods to construct cross passages linking the ECVT with the MAT.”
TBM Kirsten is undergoing significant modifications to undertake the next task of excavating the inclined pressure shaft and lining it with specially-designed concrete segments, all locally manufactured.
Measuring 1.45km in length, the shaft presents an unprecedented challenge – excavating a segment-lined tunnel of this magnitude with an extreme 47% incline using an 11m diameter TBM. Barnes said this has not been attempted on an international scale before.
Modifications to Kirsten include altering the levels of the TBM’s tanks and mechanical equipment so they remain horizontal when travelling up the incline, and converting the walkways into steps and ladderways.
Also being installed is a screw conveyor to extract excavated rock from the cutterhead to a sandwich conveyor system with face-to-face rubber belts that help constrain the crushed rock so that it can be transported down the steep slope without spillage.
To support the ongoing excavation activities, the ECVT tunnel will see the installation of additional plant and equipment. This includes an overhead crane, a conveyor transfer station, a monorail manrider for personnel access, and a rack and pinion mechanism to facilitate plant access to the TBM.
Earlier this month it was reported that completion of the full project could be delayed by up to two years. Snowy Hydro cited four factors contributing to schedule delays and likely cost increases: the mobilization and resourcing implications of the COVID-19 pandemic, global supply chain disruption and inflation affecting the cost and availability of a skilled workforce, materials, and shipping, design elements requiring more time to complete due to their technically complex nature, and variable site and geological conditions, particularly the soft ground encountered that is delaying TBM Florence’s progress at Tantangara.