ABSTRACT
Aging hydropower facilities require engineered interventions to assure resilience and enable optimal energy production. Defective pressure tunnels result in water losses, and in the long term, can raise stability concerns. An integral part of seepage mitigation consists of an extensive, tailor-made grouting strategy, where surrounding rock-mass should be integrated to the lining system. Pressure grouting improves rock mass properties, i.e. increase of intact strength, consolidation of fractured zones, backfill of karstic voids, and reduction of permeability (primary waterproofing). Furthermore, proper grouting backfills voids at the rock/concrete interface, and seals cracks and fissures within the lining segments. Enguri Hydropower Scheme has produced energy since 1980 with its circular-shaped concrete lined 15km-long pressure tunnel been completed in 1978. The tunnel was excavated through a narrow ridge of Cretaceous karstic limestones, and Lower Tertiary marl-sandstones. During a three-months plant outage, a super-intensive drilling and grouting programme was conducted through the concrete segments. Customised grout mixes (cement-based, chemical, as well as hybrid) were injected in various tunnel stretches of water-loss potential. The injection of 2.8 million m3 grouts, resulted in the substantial reduction of water-loss which in turn, proportionally increased power generation.
