SLOPE FAILURE IN DAM SYSTEM OF IMPOUNDMENT

Impoundment disorders are dangerous accidents that threaten the quality of the environment. Safe operation of desludging sites especially depends on reliable and without fault working dam system. The paper analyzes the principal reasons of the local dam failure of the ash impoundment. The impoundment used to store ash from thermal power plant. The description of the structural composition of the impoundment's dam is presented. The local dam failure of the plain ash impoundment was caused by the enlarged water seepage across the dam. The enlarged water seepage was activated by the reconstruction works on the recirculating water pipe. During forcing of the steel sheath for recirculating water pipe across the circumferential dam of the impoundment, conditions favoring seepage of water (preferred paths) originated in the surrounding area. In the expanded ash zone around the steel sheath and between its relatively smooth wall and granular environment, narrow but continuous spaces formed, representing a privileged seepage path for water. Suffosion and erosion caused formation of the fault in the impoundment's dam. Approximately 300 m(3) of ash leaked from the dam of the impoundment. Remediation works were carried out in successive steps. The created corridor of expanded ashes in impoundment's dam was disrupted by injection of sealing curtain of clay and cement. The produced erosion trench was cleaned and backfilled and compacted. The missing drainage system was constructed.