ABSTRACT
Zhinvali HPP is one of the most important water supply schemes for Tbilisi city. It was commissioned in 1985 and after almost 30 years some rehabilitation works for its 8.8 km long tailrace were considered necessary to ensure its service continuity.
The visual inspection along the tunnel showed a relevant widespread damaging state of the lining, with risk of structural instability in some stretches.
A sustainable decision-making process was implemented to address a short and a long-term rehabilitation plan. The main constraint for the planning, design and works was the limited tunnel outage for maintenance in order not to interrupt the activities of the plant for more than one month per year.
A multistage investigation program was developed to acquire knowledge of tunnel layout and of concrete lining features and to analyse the reasons of the tunnel damaging state. In the short-term planning, damages have been scanned and a priority actions list was drawn up, to ensure the tunnel functioning after outage period in the most damaged zones.
Since 2014 up to 2020 a rehabilitation plan was implemented yearly. Despite of all the constraints imposed for the execution of inspections, investigations and works, the operations successful restored the damaged zones of the tunnel, although new damages have been detected during the latest inspection.
All the data collected over time contributed to have a considerable background on tunnel conditions and to identify their sources. Considering that a short-term approach could only restore the tunnel functionality without eliminating the source of damaging, a long-term concept was then proposed. It consisted in a large-scale rehabilitation works to improve the hydraulic performance of the tunnel, reaching the original design capacity and steady operation conditions.
This paper will address and detail all the inspection and design activities carried out for this project.
