Some geotechnical aspects of raising the Mangla dam, Pakistan

Abstract

The Mangla dam project in Pakistan was the largest embankment dam project in the world when it was completed in 1967. The 260 km2 reservoir is formed by four major dams, each with a different cross-section, and each a significant structure. The original designs included provision for raising the dams by up to 12 m to offset the effects of future sedimentation. In 2000, capacity lost due to sedimentation became a significant issue. The government of Pakistan decided to exploit the raising provisions of the original design, and store flood water that was routinely being released. Following studies to confirm the most economic extent of raising, the original designs were reviewed and modified. Since the 1960s there have been advances in geotechnical and seismic engineering, changes in design parameters and information from 40 years' performance of the dams, all of which had to be taken into account in revisiting the designs for the raising. As a result, the dam cross-sections for the raised embankments have been adjusted using updated parameters, and the opportunity has been taken to address some areas of seepage that have been under observation since the original construction. Construction for a 9 m raise began in 2004 and was completed in December 2009. The total length of dam embankment after raising is 14 km, with a maximum height of 148 m. The work required 31 million m3 of fill materials, and is one of the largest dam-raising projects ever undertaken.