Wadi Dayqah Dam Curtain-Paper

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The Wadi Dayqah Dam Water Supply Scheme in Oman includes a 75 m-high concrete main dam and a 49 m-high rockfill saddle dam. After the reservoir first filled in 2010, seepage became apparent at the saddle dam’s right abutment and at the main dam’s left abutment. Züblin Ground Engineering carried out additional sealing works from 2013 to 2015.<br /><br />The foundation geology—folded, variable layers of siltstone, claystone, sandstone and limestone—made seepage control challenging. At the saddle dam, the work comprised a three-row grout curtain, generally extending to 80 m and locally to 125 m, plus an 85 m-long secant-pile cut-off wall extending 40 m below the crest. The curtain was installed using staged, pressure-controlled cement-bentonite grouting, with hole spacing progressively tightened to meet closure criteria. Difficult conditions near the dam-core/rock interface required top-down grouting in short stages. Investigation drilling and water-pressure tests informed the design and monitored performance.<br /><br />At the main dam, additional drilling and grouting targeted leakage at the left abutment. In total, approximately 24,000 m of boreholes were drilled, tested and grouted across the works.<br /><br />The sealing significantly reduced seepage at the saddle dam: with the reservoir full, measured flow fell from as much as 25 litres per second before treatment to less than 2 litres per second by April 2014. The groundwater table below the dam also declined. At the main dam, grouting reduced visible leakage from the downstream shoulder, although it had little effect on seepage collected by gallery drain holes.

Keywords

Wadi Dayqah Dam

Oman

water supply scheme

seepage control

grout curtain

secant-pile cut-off wall

cement-bentonite grouting

saddle dam

main dam abutment

groundwater seepage