Site characterization of large hydropower projects Thomas Trick*, Karam Kontar* and Gerd Klee† *Solexperts AG Mettlenbachstrasse 25 CH-8617 Mönchaltorf, Switzerland thomas.trick@solexperts.com karam.kontar@solexperts.com www.solexperts.com † Solexperts GmbH Meesmannstrasse 49 D-44807 Bochum, Germany gerd.klee@solexperts.com www.solexperts.com ABSTRACT In many countries hydropower plays an important role in the context of the energy transition contributing to the reduction of the CO2 emission through a permanent power production as run-of-river scheme as well as for energy storage as pump-storage-scheme. Nowadays large hydropower plant designs comprise tunnel, cavern and shaft excavation works known as head race and pressure tunnel or pressure shaft. The powerhouse is often placed within a large underground cavern. The results of a ground investigation phase including the determination of in-situ parameters derived from tests in boreholes drilled from the surface are crucial for a preliminary design of the hydropower plant. Additional in-situ measurements are frequently carried within an exploratory tunnel to confirm the first predictions and to characterize in detail the rock and hydraulic properties of the rock mass. Solexperts portfolio of in-situ well tests comprise the assessment of a hydraulic properties vs. depth through hydraulic testing of isolated borehole sections along the borehole axes and determination of geomechanical parameters like D- and E-modules through borehole dilatometer tests and rock stress measurements conducting hydraulic mini frac tests. Plate load tests which use surficial loading are performed in small tunnels or test adits to measure the deformation characteristics of a rock mass on a larger scale (Vrkljan et al, 1995). This paper summarizes our experience of the in-situ measurements which Solexperts carried out during the last years at many hydro power sites around the globe. Reflecting about this experience and the large data set, we gathered our lessons learned and further ideas as well as newest developments which we would like to share in this paper with consultants, project owners and other institutions to contribute towards a best practise portfolio. [1] Vrkljan, I., Kavur, B., Mehinrad, A., Ghiassi (1995) Rock mass deformability by extra large flat jack, plate load and dilatometer testings, Proceedings ISRM 8 Congress, pg. 185 - 191.