Evaluation of Rock Character Change of Dam Foundation

摘要

The water environment around the dam site changes greatly after a dam was built. As a solution the water in the reservoir transfers towards the dam foundation and the geochemical action between the water and rock will be accelerated rapidly at some sections. The main components consisting of rock are minerals of silicate and aluminum silicate. When they are hydrolyzed sufficiently some materials are formed such as real solutions or colloidal solutions of silica, aluminum oxide and oxides of potassium, sodium, calcium and magnesium. Transference of these materials in the water of dam foundation is important basis to evaluate the character changes of soft rocks (softening or argillazation) in the dam foundation. The chemical contents of SiO_2 and Al_2O_3 are higher than 50% in a few of colloidal educts of dam foundation and the content of SiO_3~(2-) in the water is abundant too. This indicates that some character changes of soft rocks have happened in part of the foundation. The particles of clay and silt in soft rock can be migrated with colloid in water too, which indicates that chemical suffosion is usually accompanied by mechanical suffosion.