David was appointed by Amberg Engineering as Chief Site Supervisor for extensive grouting works and completion of the excavation of the 15.2km headrace tunnel excavated by TBM and a 3.7km drill and blast tunnel linking the two dams.
The Uma Oya multipurpose development project is being performed in south east of Sri Lanka in central highlands in order to transfer water, to produce hydroelectric energy and to use in agriculture industry. The project consists of two concrete roller dam. The first dam will be built on Uma Oya River in Puhulpola area. Through a tunnel with 3.7km length (a transferring tunnel), the water will be transferred from Uma Oya River to Dayaraba Dam Reservoir which is built on Mahatota Oya River. A long headrace tunnel with 15.2 km length and a vertical shaft with 595 m height will transfer water from there to an underground power station. Through a tunnel with 3.6 km length, water in the power station will be directed towards Alikuta Oya River which is a branch of Kirindi Oya River. The excavation of the major 4.30m diameter headrace tunnel is done by full mechanized method and by using a double shield excavating machine. This is the first use of a TBM in Sri Lanka
Water ingress in HRT increased dramatically in December 2014. it was decided to continue with TBM excavation and grout this ingress later, when the flow had reduced. To treat the zone of water ingress it was necessary to move the TBM forward 200m so that work could be carried out behind the TBM. During further TBM excavation the flow further increased up to a peak of 440 l/s. On the 4thMay 2015 the TBM stopped and on 18th May 2015 rock mass grouting commenced.
On Completion of grouting a further 10km of TBM excavation was required with probe drilling and seismic prediction ahead of the face to ensure no similar in rush of water ocurred.
David Lees was appointed as Chief Site Supervisor for Amberg Engineering to supervise firstly the grouting works and then the tunnel excavation. With a team of up to eight expat and local engineers the work included both the 15.2km TBM tunnel and an additional 3.7km drill and blast tunnel linking two dams at the head of the project.
