Positive Cut-Off Wall in Indian Dam - ANew Technique for Difficult Geology-Paper

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The paper presents India’s first use of controlled “surgical blasting” to construct a plastic-concrete cut-off wall in exceptionally difficult geology at the Kishanganga hydroelectric dam in Jammu and Kashmir. The 1 m-thick, 134 m-long wall reaches depths of up to 35 m and is keyed into hard bedrock to prevent seepage beneath the dam.<br /><br />The riverbed overburden contained tightly packed boulders and cobbles, including very hard volcanic rock, while the underlying bedrock also had high strength. After evaluating alternatives such as hydromill trenching and large-diameter drilling, the contractor and specialist consultant selected a two-stage approach: accurately drilled and monitored blast holes were charged to fracture boulders and form the rock socket; heavy-duty mechanical clamshell grabs then excavated the trench, with chisels used for remaining obstructions and corrections.<br /><br />Borehole inclinometers and drilling logs helped control hole position, verticality and charge placement, limiting blasting to the trench footprint. Water-pressure tests before and after blasting indicated that the bedrock was not damaged. Trenches were supported with bentonite slurry, checked for profile and verticality, and filled by tremie with low-strength plastic concrete. Alternating primary and secondary panels, with overlaps, provided wall continuity.<br /><br />The project demonstrated that carefully controlled drilling and blasting, combined with conventional grabbing and chiseling, can enable cut-off wall construction in highly bouldery, hard-rock conditions where other methods may be impractical. Close monitoring and quality control were central to managing trench stability, alignment, joints and concrete placement.

Keywords

India

Kishanganga hydroelectric dam

surgical blasting

plastic-concrete cut-off wall

seepage control

hard rock geology

boulders and cobbles

trench excavation

bentonite slurry

quality control