Internal Structure of an Earth Rolled Dam
The dam consists of an impervious center section, impervious upstream blanket, upstream chalk blanket and downstream chalk berm or shelf. The main portion of the embankment rests on valley sands and gravels which permit some movement of water beneath the dam. The upstream impervious blanket reduces the amount of water that passes beneath the dam and pressure relief wells at the toe of the rolled earth embankment relieve any excess water pressure that may develop beneath the downstream chalk berm.
Approximately 28,000,000 cu. yds. of rolled earth and 22,000,000 cu. yds. of dumped chalk from structual excavation are a part of the dam. The rolled earth is selected material containing sufficient amounts of clay to make the central section of the dam impervious. The earth was placed in the embankment to meet exacting technical standards as to moisture content and compaction. Mammoth power shovels and large bottom and end-dump trucks, capable of carrying 35 yards or 50 tons of earth at one time excavated and hauled the earth.