Operation of Norwegian Hydropower Plants and Its Effect on Block Fall Events in Unlined Pressure Tunnels and Shafts

The main objective of this study is to investigate the effect of hydropower plant operation on the long-term stability of unlined pressure tunnels of hydropower plants in Norway. The authors analyzed the past production data of some hydropower plants to find out the number of starts/stops and the frequency and magnitude of load changes. The study demonstrates that an average of 200–400 start/stop events are occurring per turbine per year for the analyzed period, with an increasing trend. Currently, 150–200 large load changes per turbine smaller than 50 MW are occurring every year, and this is expected to increase by 30–45% between 2025 and 2040 for one of the studied power plants. Most importantly, the monitored pressure transients and pore pressure response in the rock mass during real-time operation at Roskrepp power plant are presented. A new method is proposed to calculate and quantify the hydraulic impact (HI) of pressure transients on rock joints and the effect of duration of shutdown/opening, which is found to be the most dominant parameter affecting the magnitude. The results show that faster shutdown sequences cause unnecessary stress in rock mass surrounding pressure tunnel. The hydraulic impact (HI) can be more than 10 times higher when the shutdown duration is reduced by 50 percent. The study recommends that duration of normal shutdowns/openings in hydropower plants should be slower so that hydraulic impacts on the rock joints are reduced and cyclic hydraulic fatigue is delayed, prolonging the lifetime of unlined pressure tunnels and shafts.

Norwegian Design Principle for High Pressure Tunnels and Shafts: Its Applicability in the Himalaya

Cost effective, safe and long term sustainable hydropower development is key for the lasting economic growth in the Himalayan region. Increasing pressure towards the use of renewal and environmentally friendly energy for industrial growth and daily household use will force the Himalayan region to exploit hydropower energy more extensively. The traditionally used design approach of fully lined underground waterway system is costly and financially unfeasible as well as an obstacle to attract investment in the hydropower sector in the Himalaya. Hence, more innovative solutions are needed to make hydro generated energy more cost effective and as a sustainable energy solution in the long term. This paper briefly describes the geological set-up of Scandinavia, history of Norwegian Hydropower and reviews the design principle used to develop the underground waterway system in Norway. Brief comments are also made on the applicability of these principles in the Himalayan region. It is anticipated that more discussions will be made in the future on the geo-tectonic environment of the Himalaya and suitability of Norwegian design principle in the Himalayan region.DOI: http://dx.doi.org/10.3126/hn.v14i0.11254HYDRO Nepal JournalJournal of Water, Energy and EnvironmentVolume: 14, 2014 JanuaryPage: 36-40

Evaluation on the Potential Use of Shotcrete Lined High Pressure Tunnel at Upper Tamakoshi Hydroelectric Project

Optimization of rock support is a key factor for successful use of underground space for hydropower development in the Himalaya. Therefore, finding innovative, optimum and economic solution will be the only way to guarantee such optimization. A main issue is to determine the extent of hydraulic fracturing and assess the water leakage possibility during the operation of such tunnels. The leaked water not only causes economic loss but also may severely affect the stability of tunnel, valley side slopes and the environment.The use of fully concrete/steel lined pressure tunnels against hydraulic fracturing in the rock mass is a costly alternative. Hence, it is advantageous to explore possibilities of minimizing the length of the concrete or steel lining in high pressure tunnels and shafts. A proper assessment of hydraulic fracturing of the rock mass plays an important role in this endeavor.This paper evaluates whether or not hydraulic fracturing (splitting) will occur at the 4,746m long shotcrete-lined high pressure headrace tunnel of 456 MW Upper Tamakoshi Hydroelectric Project (UTKHEP). The Upper Tamakoshi HEP is a high head project (gross head 822m) and the proposed shotcrete lined high pressure headrace tunnel will experience maximum hydrostatic pressure head of 40 bar (400m water column) at normal plant operation. To check the possibility of hydraulic fracturing, both deterministic and two dimensional numerical modeling techniques have been used. In addition, the paper also highlights the importance and challenges to be faced while estimating representative input variables needed for both deterministic and numerical modeling.DOI: http://dx.doi.org/10.3126/hn.v10i0.7118 Hydro Nepal Vol.10 January 2012 73-80