Geological and geotechnical evaluation of the tunnel site of the Koto Hydropower Project, Khyber Pakhtunkhwa, Pakistan

Hydropower projects provide excellent opportunities to cope with rising energy demands; however, their geological and geotechnical evaluation is fundamental to ensure their long-term performance and stability. Thus, geological and geotechnical investigations were carried out to evaluate the feasibility of a tunnel (7 m diameter and 1880 m length) for the Koto Hydropower Project, Khyber Pakhtunkhwa, Pakistan. Five investigation boreholes with a cumulative depth of 145 mwere drilled and samples were collected for qualitative observation and laboratory analyses. The geotechnical investigations include Lugeon and permeability tests to estimate the hydraulic conductivity of the associated rocks. In the boreholes, lithologies and discontinuities such as joints, fractures, veins and shear zones were identified. Lithological logging, rock quality designation and percentage core recovery were used to understand rock behaviour and strength. The rocks encountered are mainly gabbronorites and granodiorites with some amphibolites. The bedrock strength is designated as R4 (strong) with a minor amount of R3 (moderate), indicating suitability and feasibility for tunnel construction. The Main Mantle Thrust is the major tectonic feature, which is located towards the southern side of the study area; however, seismicity along it is not significant. The geological and geotechnical investigation indicated the suitability of the tunnel site for construction.