Remedial Grouting at Mosul Dam, Iraq-Paper

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Mosul Dam, Iraq’s largest dam, was built on a foundation containing gypsum and anhydrite layers prone to dissolution, karst formation, and internal erosion. Seepage and sinkholes raised serious safety concerns, and a 2016 USACE risk assessment identified multiple high-risk failure modes. The dam’s reservoir level had been restricted, affecting power generation and irrigation.<br /><br />In 2016, Trevi was awarded an emergency rehabilitation contract, with USACE overseeing design and supervision. The main work focused on repairing the grout curtain along the dam foundation, using drilling and grouting from both the 2,200 m foundation gallery and the dam crest. Operations were complicated by deep, variable geology, high artesian pressures, restricted gallery access, and the need to avoid disturbing the embankment core.<br /><br />The project used specialized drilling rigs, three mixing plants, 20 batching-and-grouting units, and a 20 km grout conveyance network. Automated monitoring software controlled injections and recorded more than 900 million data points. Flexible drilling and grouting methods, varied grout mixes, and staged injection were adapted to local ground conditions.<br /><br />From late 2016 to July 2019, crews drilled or redrilled 667,800 m and grouted 5,390 boreholes, placing approximately 40,800 m³ of grout. Verification testing indicated substantial improvement: 81% of tested stages had permeability readings of 1 Lugeon or less, and 98% were 3 Lugeons or less. Instrumentation also showed improved hydraulic conditions.<br /><br />The rehabilitation reduced the assessed risk substantially, enabled the reservoir to return to levels last reached in 2005, and allowed the spillway to reopen. Trevi also trained Iraqi Ministry of Water Resources personnel to operate and maintain the equipment and continue grouting activities.

Keywords

Mosul Dam

Iraq

grout curtain

dam rehabilitation

seepage control

sinkholes

USACE

drilling and grouting

foundation stabilization

hydraulic risk reduction