Adaptable Robbins Double Shield excavates Turkey’s Tough Ground
In the mountainous terrain of Central Turkey, a hard rock heavyweight is excavating through demanding conditions. The 10.0 m (32.8 ft) diameter Robbins Double Shield TBM was launched in spring 2012 following Onsite First Time Assembly (OFTA). The excavation is part of the Kargi Kizilirmak Hydroelectric Project, what will become one of the country’s largest hydropower stations to date. Dedicated crews for contractor Gülermak, project owner Statkraft AS, and Robbins are guiding the machine through changeable geology including mixed weak ophiolite with high clay content and water inflows.
The massive hydroelectric project consists of an 11.8 km (7.3 mi) long headrace tunnel through a mountainside near the town of Osmancık. Ground is expected to consist of volcanic-based rock with softer limestone for the first 3.0 km (1.8 mi), giving way to harder geology including marble for the rest of the route. This change means that segmental lining of the tunnel will take place for the first 3.0 km (1.8 mi) only, requiring a highly adaptable machine design that is able to line with everything from segments to conventional ground support. The remainder of the tunnel will be supported with ring beams and rock bolts, as well as a final lining of shotcrete. The types of ground support made the design of the TBM and back-up unique—there are many features that require adequate space, from shotcreting to rock drilling to segment handling.
As of August 2012, the TBM had advanced over 400 m (1,300 ft) despite extremely difficult ground including unexpected fault zones and inflows of water and mud. More than 150 people are employed at the site, with Robbins field service and Gülermak personnel working together to overcome the conditions. “We have had some very impressive efforts by the Gülermak and Robbins teams,” said Glen Maynard, Robbins Field Service site manager. “After the TBM had bored 175 m (574 ft) with a temporary conveyor system, tunneling was interrupted to install the permanent tunnel conveyor system. Gülermak completed this installation in six days; on day seven the Robbins Continuous Conveyor System was operational, and normal boring operation was resumed.” Maynard continued to say that early signs were promising with regards to TBM advance, with shifts topping 15 m (49 ft), and 20 m (66 ft) daily advances becoming a regular occurrence.
The Kargi Kizilirmak Hydroelectric Project, located in Corum Province about three hours from Ankara, will source water from the Kizilirmak River to generate clean electricity. Up to 470 GWh will be generated annually—enough to power about 150,000 homes. The project, for Norwegian company Statkraft AS, is scheduled to go online by the end of 2013.