Лаборатория геологии техногенных процессов
Maximovich N.G. Dams on gypsiferooous - a possible source of Disaster // Internanional Symposium on Latest Natural Disasters - New Challenges for Engineering Geology, Geotechnics and Civil Protection: Abstract Book, September 5-8, 2005. Sofia, Bulgaria. Sofia, 2005. P. 65.
Dams on gypsiferous rock - a possible source of Disaster
MAXIMOVICH, N. G.
One of the most negative conditions of building of hydro-engineering constructions, which can lead to disaster, is a gypsiferous rock foundation. Building of water-retaining constructions results in change of hydrodynamic regime and appearance of waters undersaturated with calcium sulfate. It creates conditions for dissolution of gypsum. Activization of karst also can be connected with increasing of fissuring as a result of filtrational deformations and rock weathering during construction. Additionally, there is a certain role of increasing of rock solubility caused by pressure of construction. Solution of gypsum contained in dispersive rocks can cause suffusion processes. Such processes lead to accidents.
In number of cases they refused from building because of the presence of gypsum in dam foundation. For instance, in Provence (France) gypsiferous marl was exposed during construction. As a result, the building was stopped. Construction of small hydroelectric power station on the Iren River in the Perm region also was stopped. In Iraq, one of the reasons of refusal from favourable topographical dam location on the Fatha River station was presence of rocks containing up to 60 % of gypsum and anhydride.
Sometimes dam construction on gypsiferous rocks leads to Disasters. For example, one of the reasons of destruction of Sant- Francis dam (California, USA ), entailed human victims, was dissolution of gypsum contained in clay conglomerate foundation. Cases of water loss from water reservoir are known at small dams with gypsiferous rock foundation - on the Оsa River (the Angara River basin), in Oklahoma and New Mexico (USA). The problem of protection of gypsum from dissolution arose during construction of the Yerevan hydroelectric power station (Armenia), Brently Dam (New Mexico, USA) and some dams in Iraq. The question about reliable filtering-proof actions for protection of gypsum in foundation was on the agenda during designing of Irganajskaya, Nizhnekafirniganskaya and Rogunskaya dams.
During construction of dams on gypsiferous rock it is necessary to carry out careful geological engineering survey including mathematical modelling for a substantiation of filtering-proof actions for gypsum protection. Kama hydroelectric power station (Western Urals, Russia) is an example of realization of such actions (Figure). It was constructed in 1954 on the Kama River and now is situated on the territory of the city Perm.
Fractured gypsiferous rocks of Sheshminskiy and Solikamskiy horizons of Ufimskii series of Upper Permian are found in affected zone of construction.
Hydrochemical and hydrodynamical regime data showed that after construction processes of desalination of underground waters started to develop in dam foundation, which usually make processes of dissolution of gypsiferous rocks more active. Filtering-proof actions (cement barrier and drainage) provided by the project appeared were not very effective. This raised the question of consolidation of cement barrier and gelling solution was developed by the Problem laboratory of Geological Department of Moscow University. It was first domestic experience of usage of silicate solution for plugging of fractured rocks in dam foundation.
Plugging effect of this solution is reached due to gelling from colloid solution (sol) after its introduction into massive by injection, and high penetrating ability is provided with its low viscosity. After consolidation of cement barrier, filtration coefficient decreased in some times.
Postinjection processes appearing under silication of water-saturated fractured gypsiferous rocks, provide safety of gypsum and efficiency of cement barrier raising in time that increases stability of dam. This is confirmed with mathematical modeling data and natural observations. Experience of injection consolidation for prevention of disaster can be used on other hydraulic engineering constructions.