Grouting a Dam Cutoff in Cavernous Limestone

Cutoff treatment at Logan Martin Dam was especially important in providing a stable and watertight foundation. Complex cavity systems occurred in the fractured dolomitic limestone bedrock. Treatment of interconnected open passageways in these cavities required massive filling to retard serious leakage. Also comprehensive grouting was necessary to tighten and check all weathered parts of the foundation. Bedrock was explored in detail by drilling cored holes for all primary positions along the curtain line. Information from these was used to adjust all grouting to compatible limits with geologic conditions and grout hole depths for intermediate positions were modified to confirm projected primary stage data. Substantial grout consumption was expected and use of inert fillers was planned when experimental work started. Fly ash was chosen after demonstrating its adequacy. The grouting operation was concurrently evaluated for effectiveness using techniques that show logical terminal injection points.