Himalayan Geology, Vol. 43 (2), 2022, pp. 397-405, Printed in India

Feasibility study of Weir Site of the Koto Hydropower Project, District Lower Dir, Khyber Pakhtunkhwa, Pakistan: Geological and geotechnical approach

NASAR KHAN^1&2*, MUHAMMAD AWAIS³, MUHAMMAD EJAZ SIDDIQUI⁴, KHAN SHAHZADA⁵, JAWAD KHAN¹

¹Department of Geology, University of Malakand, Chakdara 18800, Khyber Pakhtunkhwa, Pakistan

²Department of Earth and Environmental Sciences, KU Leuven, Celestijnenlaan 200E, Heverlee 3001, Belgium

³Department of Geology, University of Swabi, Anbar 23561, Khyber Pakhtunkhwa, Pakistan

⁴Sarwar and Company (Pvt.) Limited, Rawal Town 45510, Islamabad, Pakistan

⁵Department of Civil Engineering, University of Engineering and Technology, Peshawar 25120, Pakistan

*Email (Corresponding author): nasar_khan@uom.edu.pk

Abstract: Geological and geotechnical investigations were carried out to evaluate the feasibility of weir site of the Koto Hydropower Project in the vicinity of Koto Village, District Lower Dir, Khyber Pakhtunkhwa, Pakistan. The feasibility of weir site is determined by lithology identification and discontinuity surveying coupled with core recovery (CR), rock quality designation (RQD), permeability test, water pressure test, water table measurement, standard penetration test (SPT) and cone penetration test (CPT). These measurements indicate that the weir site is comprised of a thick layer of overburden/River Born Material (RBM) underlain by moderately jointed igneous (diorite, andesite and gabbronorite) and metamorphic rocks (amphibolite patches). The thickness of overburden/RBM fall within the optimum feasible range for weir construction after suggested excavation, otherwise, its presence generally reduces the feasibility. Permeability and water pressure tests were performed at specific depths in the boreholes to estimate hydraulic conductivity of the sub-surface rock masses and hence provide an image of the subsurface discontinuities. Joints and fractures analyses of the drilled core samples resulted into moderately jointed sub-surface rocks having an average three to four joints sets per meter depth filled

with clays, calcite and iron oxides. As a result of these joints and fractures water loss occur and hence reduces suitability for weir construction. The permeability, water pressure tests and joints analysis advised a grout curtain below the reservoir foundation to ensure its stability and feasibility. The overall bed rock strength is designated as R4 (strong) with minor amount of R3 (weak) on manual index test that implies suitability for weir construction after engineering considerations. Thus, the present study suggests that the foundation is feasible for weir construction.

Keywords: Koto Hydropower, Feasibility, Energy, Geotechnical, RQD, Pakistan.