Himalayan Geology, Vol. 44 (1), 2023, pp. 97-105, Printed in India

Formation of stress relief discontinuities due to removal of normal load from foundation

Rocks, Tarbela Dam, Pakistan

SOHAIB AHMAD¹, NOOR ZADA AFRIDI², TUFAIL ^AHMAD3, MUHAMMAD IMRAN SHAHZAD^3,4,

MUHAMMAD AWAIS⁵*

¹College of Science and Engineering, James Cook University, Townsville, Queensland, Australia

²Pakistan Mineral Development Corporation (PMDC), Peshawar, Khyber Pakhtunkhwa, Pakistan

³Associated Consulting Engineer (Pvt) Ltd

⁴University of Azad Jammu & Kashmir, Muzaffarabad, Pakistan

⁵Department of Geology, University of Swabi, Swabi, Khyber Pakhtunkhwa, Pakistan

*Email (Corresponding author) : awais.geo89@gmail.com

Abstract: The current paper presents a case study of the Tarbela Dam (Pakistan) based on highly deformed Precambrian schistose rocks. These rocks are exposed after removing the normal load from the foundation rocks. Stress relief discontinuities are induced by removing the normal load, which significantly influences the hydraulic conductivity of underlying rock mass. The ingression of water seepages through these discontinuities decreases the shear strength of foundation rock mass to a considerable extent. It subsequently enhances the potentialities of rock mass failure along planes of weak discontinuities. Water pressure tests were conducted during pre- and post-excavation stages to acquire the hydraulic conductivity at the same elevation of the foundation area. The hydraulic conductivity measured at the preexcavation stage is less than its value at the post-excavation stage. It is indicating that stresses are released after removal of normal load from foundation rock mass with marked impact on dilation and enhanced amount of hydraulic conductivity (at post-excavation stage).

Keywords : Stress relief joints, rock mass sliding, Hydraulic Conductivity, Tarbela dam, Precambrian schistose rock