Duck River Dam is a 135-foot high dam currently under construction in northern Alabama. The dam is a hybrid structure comprising of rockfill embankment sections on the abutments and a 300-foot-long center Roller Compacted Concrete (RCC) gravity spillway structure with an ogee crest. The dam is situated on sedimentary rock, consisting of alternating layers of shale, sandstone and interbedded shale and sandstone of the Pottsville Formation. Results of a test grouting program suggested that grout takes could be variable, with high grout takes in some of the sand/shale contact zones. The Grout Intensity Number (GIN) method was used to perform the grouting, but some aspects of the method were modified to incorporate some North American grouting practices. These included (1) use of a stable and balanced grout mix that achieved high flowability as well as high resistance against pressure filtration, (2) lowering grouting pressures to limit the potential for jacking of highly weathered shale unit at the upper reaches of the abutments, and (3) use of water pressure testing in final verification boreholes to assess the effectiveness of the grout curtain and to confirm that closure of the curtain was attained. Stability of the grout mix was obtained using diutan gum rather than the more traditional bentonite. A tightly closed two-row curtain with maximum spacing at the tertiary level, and use of quaternary and higher order holes as necessary to achieve closure, was selected instead of a triple-row curtain. Temporary stoppage of the RCC placement after producing a 15-foot thick cap provided excellent confinement to accommodate higher injection pressures in the upper rock layers. Ways in which the results of borehole televiewer and water pressure testing were used to (1) estimate the theoretical grout volume of grout, and (2) evaluate the effective injection pressures required to achieve the target penetration or reach of the grout are described.
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