Jinvali dam and hydropower plant - Tunnel rehabilitation

Jinvali hydropower complex was commissioned in 1985. The scheme includes a 102 m high earthfill dam, a shaft water intake, a spillway and bottom outlet, an underground powerhouse with 4 Francis turbines, an 8.8 km long free flow tailrace tunnel, a forebay and a 36.7 km long water way for the water supply to Tbilisi, the capital of Georgia. 

Considering that the hydraulic structures are in operation for more than 35 years, the planning and implementation of certain rehabilitation works has been deemed necessary.

Existing local defects and erosion of concrete lining, poor rock, bad concrete quality and seepage observed at different sections of the tunnel calls for frequent observations and systematic rehabilitation works.   

In 2014, Gruner Stucky performed a detailed inspection of the tunnel, followed by assessment the status and proposition of short- and long-term rehabilitation concept, allowing to keep tunnel operable.   

The following activities have been performed from 2014 up till now to achieve above:

• Investigation works, design and site supervision, with Visual inspections,
• Concrete lining sample lab tests on strength,
• Water tests of the aggressivity to concrete and reinforcement ,
• Tunnel hydraulic capacity analysis,
• Geoelectric tomography,
• Ultrasonic Ground and Penetrating Radar,
• 3D laser scanning,

The Rehabilitation works, design and site supervision, have 2 approaches:

Short term concept – Which includes urgent rehabilitation works, to be done on a yearly based. Due to a large extend of damages, a systematic and consistent rehabilitation by systematic grout-ing, chemical grouting, replacement of concrete lining and rehabilitation of honeycombs, including inves-tigations and monitoring, was carried out from 2014 up till now.

Long term concept – this involves a large scale rehabilitation works to improve the hydraulic performance of the tunnel, reach original design capacity and steady operation conditions were analyzed for:

• The replacement of the existing tunnel with a new one,
• The construction of a bypass for the first 3 km section of the tunnel,
• The replacement of the existing lining with a new one with pressurized flow conditions. 

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