TBM RECORDER TBM excavation conquers Peruvian Andes Jan 2012
Desiree Willis, Technical Writer, The Robbins Company
- Extreme geological conditions and dramatic rock busting events have been tamed to complete TBM tunneling for the Olmos Trans-Andean tunnel in Peru.
Triumphant TBM and crews
- After four long years of determined effort, the 5.3m diameter Robbins main beam gripper machine and its crews achieved breakthrough in late December to complete 12.5km of tough TBM advance under high cover and through varied volcanic strata. President Ollanta Humala of Peru and other Government officials joined contractor Odebrecht Peru Ingenieria y Construccion to mark the significance of the achievement.
- The project is part of a larger scheme that will transfer water from the Huancabamba River on the eastern side of the Andes to drought-ridden areas on the Pacific Ocean Watershed.
- To complete the connection, the Robbins machine had to pass under mountain cover of up to 2,000m. This held tremendous insitu rock stresses that resulted in more than 16,000 rock bursting events. About 17% of these were classified as severe.
- "I am satisfied with the performance of the machine, it was very powerful and performed well in the high-frequency rock bursting conditions," said Hiroshi Handa, Production Manager for Odebrecht.
Extreme rockbursting caught on camera
- The extreme nature of the geology, that included andesite, dacite, tuff, schist, and pyroclastic breccias of up to 250 MPa in UCS, was unforeseen and required in-tunnel machine modifications as rock bursting became more severe. Crews removed the roof shield fingers and installed the McNally Support System, manufactured by Robbins under license from C&M McNally.
- The system consists of steel slats anchored to the roof of the tunnel by steel straps and rock bolts, effectively containing loose and unstable rock. These steel slats form an umbrella that allows the crew to work in a safe environment.
- Other changes included reinforcements to the cutterhead and relocation of work platforms and the operator's cab. The modifications were successful in reducing safety hazards.
- No serious injuries occurred during continued rock bursting, in part because of a pre-drilling and sequential boring policy developed by Odebrecht. During a push, workers stayed 40m back behind the face and cutterhead support for a period of 30 minutes which allowed rock deformations without risking harm to workers.
- "I am proud to have an extraordinary working team," said Handa. "Despite all of the difficulties and challenges they never lost confidence. There were days with advance rates of 35m (115ft), and others with rates of only 50cm (20in) through the most difficult conditions. The most important thing is that the designer, TBM manufacturer and contractor worked together to make the necessary machine adjustments and complete this TBM undertaking."
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