Planning in Mechanised Headrace Tunnelfor the Uma Oya Project, Sri Lanka

Abstract: Uma Oya Multipurpose Development Project is in Sri Lanka. This project involves 2 RCC Dams connected by a Link tunnel constructed by D&B method. The water will be transferred from the first dam to the 2nd dam and then it will be transferred through a long 15.4 Km Headrace tunnel to the top of a 618 m deep pressure shaft that feeds the high-pressure water to an underground powerhouse for a generation of electricity then water will be passed through Tailrace tunnel to the downstream for agricultural purpose. The Headrace and Tailrace tunnels are being excavated by two 4.3 m diameter Herrenknecht double shield TBMs. This paper reviews the project planning of Headrace tunnel as a main part of the project, and all the unforeseeable conditions which were happened in the Headrace tunnel and in some duration makes a Headrace tunnel as a critical part of the project time schedule, and time schedule revised and engineering to catch up the good time planning until the breakthrough. In this paper, the effective parameters and objectives for excavation, maintenance, groupings, and all other hard rock tunnelling parameters will be reviewed.