Foundation Exploration and Geologic Studies at Chickamauga Dam

Engineers and geologists seldom encounter more difficult foundation problems in the construction of a large dam than those which prevailed at Chickamauga Dam. The rock forming the foundation of the dam consists mainly of thin-bedded, pure to argillaceous limestone with thin interstratified beds of bentonite and shale. The rocks are intricately folded and faulted, and are quite cavernous, especially in the zones of structural weakness. All of the foundation problems, including the heavy overburden, are related, directly or indirectly, to the structure and solubility of the rock. By carefully logging, correlating, and plotting all data made available from many hundreds of coredrill holes of both small and large diameters, it was possible to reconstruct the complex foundation conditions, in detail, in advance of actual excavation. This detailed geologic work aided the engineers in determining not only the depth to which excavation was necessary, but also the extent and character of foundation treatment that were necessary.