Impervious liners in dam construction

Geological & Geophysical Consultants

Compacted granular soils with small additions of bentonite have been used to build geotechnical structures such as impervious liners and cores of zoned earth dams. The effects of the addition of bentonite on the silty sand are reflected by an increase in the plasticity index and a decrease in hydraulic conductivity.The bentonite is naturally occurring clay which is commercially mined. In dam building it is useful because, when it is wet, it swells to many times its dry volume.

The water dam of Kolhiki (Greece), constructed from the KARKANIAS ENVIRONMENTAL CO. SA, is one uniform earth dam using as impervious diaphragm of cement-bentonite in the foundations (cutoff trench) and impervious layers of sand-bentonite in the embankment area.

In this dam the high quality Premium Gel Sodium Bentonite of CETCO (Colloidal Envinronmental Technologies Company) is used to decrease the hydraulic conductivity of the soil to the final values of 10-7cm/sec.

“The mixed blanket method for the construction of the impervious layer of sand-bentonite in the embankment area is applied for the first time in Greece” says Mrs Christina Konstantinidou, Civil Engineer, responsible of the quality control of the construction works , “and this case will be used as a pilot application for the future earth dams construction in the future.

The impervious layer is extended all along the dam embankment area, from the foundations to the top. The mixed blanket method mixes bentonite with the first 250 - 300 mm of soil. The area to be treated is first cleared of loose rocks and vegetation, then it is lightly harrowed. After the bentonite is spread it is mixed with the existing soil by lightly harrowing and then compacting with a roller. The impervious layer acts completely as impermeable barrier to the water.”

(*) Photos: Courtesy of Mrs Christine Konstantinidou