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

Abstract

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 Koto Hydropower Project, Khyber Pakhtunkhwa, Pakistan. Five investigation boreholes with a cumulative depth of 145 m were drilled and samples were collected for qualitative observation and laboratory analyses. The performed geotechnical investigations include Lugeon and permeability tests to estimate hydraulic conductivity of the associated rocks. In the boreholes, lithologies and discontinuities such as joints, fractures, veins and shear zones were identified. Lithologic logging, rock quality designation and percentage core recovery were performed to understand rock behaviour and strength. The rocks encountered are mainly gabbronorites and granodiorites with some amphibolites. The bed rock strength is designated as R4 (strong) with minor amount of R3 (moderate) that indicates suitability and feasibility for tunnel construction. Main Mantle Thrust (MMT) is the major tectonic feature which is located towards the southern side of the study area, however, seismicity along it is optimal. The geological and geotechnical investigation deciphered that the tunnel site of the project is feasible for construction.