Assessment and Remedial Measures for Persistent Seepage in the Right Abutment of Sarobi Small Dam, North Waziristan, Pakistan

Abstract

The Sarobi small dam having crest length of 134.5 m and height of 31m, constructed on Ping algad/stream near Sarobi village, North Waziristan, Pakistan, has exhibited a persistent seepage problem since its completion in 2019, preventing the reservoir from attaining and sustaining its designed water level. Despite perennial inflow, observations during construction and subsequent floods indicated leakage concentrated in the right abutment near the spillway. Geotechnical investigations, including borehole data and geological mapping, revealed highly fractured and weathered strata consisting of alternating limestone and weak shale layers, contributing to seepage through the right abutment. Visual inspections confirmed piping and seepage at the downstream face corresponding to reservoir levels. This paper presents the investigation findings, evaluates the geological controls influencing seepage, and proposes two remedial solutions: construction of a 75 m long and 4.5 m wide clay core to create an impermeable barrier, and a targeted drilling-grouting program to seal fractured zones. Cost to benefit ratio, field implementation considerations, and the necessity for expert site monitoring and critical design reviews are also discussed in this paper.