ABSTRACT
Uma Oya Multipurpose Development Project is under construction in Sri Lanka. This project involves 2 Rolled Concrete Core (RCC) Dams connected through a tunnel currently under construction by Drill and Blast method. The water is transferred from first diversion dam to the 2nd regulatory dam and from which, it will be transferred through a 15.2 km headrace tunnel to the top of a 650 m deep drop shaft that feeds the high pressure water to an underground powerhouse and turbine chamber for generation of 120 MW of electricity. Tailrace tunnel conveyance the water from the powerhouse to the outlet of the project. The plan was to excavate headrace and tailrace tunnel by two 4.3m diameter double shield TBMs. This paper will review the history of the Tailrace Tunnel along with the geology of the site. The operation of TBM in Tailrace tunnel will be discussed in more detail, focusing on the challenges of excavating through the hard rock.
