Túnel Emisor Poniente II will relieve overtaxed wastewater lines in three key municipalities home to 2.1 million people. The areas are prone to wastewater overflows of 2m or more during the region’s rainy season.
A Robbins spokesperson said: "The design of the TEP II machine was based largely on experience from past Robbins projects, in particular the Kargi Kizilirmak Hydroelectric Project in Central Turkey. At Kargi, Robbins supplied a 9.84m diameter Double Shield TBM, based on initial geologic reporting of fractured hard rock. Within 80m of launch, the geology became substantially more difficult than expected, consisting of blocky rock, sand, clays and water-bearing zones. The machine required multiple bypass tunnels and major modifications before it could resume excavation. "Modifications included a custom-built canopy drill and positioner for enhanced drilling and ground consolidation, gear reducers to adjust torque and RPM to changing ground conditions, and short stroke thrust jacks to double total thrust capabilities.
"After the modifications, advance rates increased dramatically in the difficult ground and soared to 723m in one month as conditions improved."
