ABSTRACT
Uma Oya Multipurpose Development Project is under construction in Sri Lanka. This project involves 2 Roller-Compacted Concrete (RCC) Dams connected through a link tunnel, Headrace Tunnel, 3 shafts as escape shaft (3.7m diameter in depth of 90m) in MAT, Surge Shaft (3.7m diameter in depth of 90m 135m) & Pressure Shaft (3.2m diameter in depth of 90m 618m) on Headrace Tunnel. The water will be transferred through a 15 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. A RBM 600 machine from Herrenknecht has been used in Shafts constructions by raise-boring method. Methodology was based on drilling the pilot hole from the top to the bottom and reaming from the bottom to the top. For having the best accuracy, RVDS system used in this project to minimise the deviation in Surge & Pressure Shafts. During the pilot drilling of pressure shaft (618m), two sudden water lost have been encountered, which made good experiences. In this paper the method statement, problems & solutions will be reviewed for all 3 shafts, with more emphasize on pressure shaft in this project.
