ABSTRACT
Haig Mill Dam was constructed in 1993 and 1994 for water supply in the Dalton area of northwest Georgia. The 17m (55 ft.) high embankment created a ½ million m2 (110 acre) reservoir. Foundations underlying the central portion of the reservoir site consist of upper Ordovician highly karstic limestones of the Valley and Ridge fold and thrust belt.
The initial design of the foundation treatment for the embankment was to include construction of a 23m (75 ft.) deep triple line grout curtain within the karstic limestones. During construction of the grout curtain it was found that the grout holes collapsed through the karst voids when they were drilled with a high powered percussion rig. This made it impossible to insert packers and to use conventional upstage grouting techniques. This paper describes the nature of the karstic rock encountered, the difficulties encountered and techniques used during the grouting program, the results obtained from before and after packer tests in two test grout sections and the amendments that were made to the design of the dam during construction to accommodate the karst conditions. Grouting of the karstic limestones was found to be highly variable and consistent closure of the curtain through tertiary and quaternary grout holes was difficult to achieve.
During construction, additional parametric seepage analyses were completed based on the encountered site conditions. As a result of these analyses, modifications were made in the overall seepage control system design of the dam. The final configuration of the embankment consists of an upstream clay blanket, a 6.7m (22 ft.) deep grout curtain beneath a core trench keyed into rock, and a downstream blanket drain and pressure relief trench system. The seepage control system has been designed to reduce reservoir water losses, minimize seepage gradients through the karstic foundations, relieve potential pressures within the downstream portions of the embankment, and control piping of fines through the embankment and underlying rock.
