Safety evaluation and rehabilitation plan of Masjed Soleyman rockfill dam with large post construction deformations

Abstract

Rockfill dams can tolerate deformations, but large post-construction settlements exceeding design limits may pose significant safety risks to these structures. Despite extensive researches on dam analysis and design, studies addressing the combined effects of rockfill creep and persistent high pore pressure in a dam core remain limited, particularly for dams with extreme deformations. This study analyzes 177 m high Masjed Soleyman dam, where the 20-year monitoring has recorded about 6 m crest settlement and 1.8 m downstream shell displacement. The substantial settlement has caused multiple cracks in the dam crest, including a primary crack with a 30 cm aperture. Additionally, two prominent shear zones have developed parallel to the dam axis on the upstream and downstream surfaces. 3D finite element modeling and back analysis were used to evaluate the dam static and dynamic behavior during construction, initial impoundment, and operation stages. The study revealed two primary mechanisms driving the dam exceptional deformations: high excess pore pressure in the core that reduces effective stress, and creep/particle breakage in the rockfill shells that weakens lateral confinement, leading to the core softening and distortion. SEE-level seismic analysis indicated potential crest settlements of 4.15 m, exceeding acceptable safety thresholds for dam operation. The study revealed that 50% pore pressure reduction by controlled core water content, and wet rockfill compaction during construction, could have reduced settlements by 65%. The proposed rehabilitation plan, which includes rebuilding the crest and thickening the downstream shell, may lower future settlements by 30–40%, offering an effective solution for similar dams.