Effectiveness of leakage control after application of permeation grouting to earth fill dam

Abstract

This study describes the effectiveness of permeation grouting applied for remedial works of the defected earth fill dam located in Korea. A small cavity was discovered in some part on the crest of the dam when the reservoir water level rose to 150m after the first impounding in June 1998. Although the cavity was backfilled with gravel and rubble, collapsing, of the sinkhole was continuously taking place. Thus, a comprehensive investigation such as electric resistivity test borehole test, tracer test et al. was planed and executed to detect the leakage and the sinkhole developed in the earth dam. Based on the results of the investigation, the compaction grouting program was carried out in June 2000. Observations made after the completion of the compaction grouting showed that the leakage generally decreased below the reservoir of elevation 138m. However, the leakage and turbidity through the embankment increased over the elevation 138 m. The possibility of weakness formation in dam body was arisen around the water elevation 145≈150 m. Thus, the permeation grouting method after compaction grouting application was applied for additional remedial work of the defected dam to establish the permanent safety. Permeation grouting method, combining with fracture grouting, was recommended for the core zones. Permeation grouting with either particulate or chemical grouts is utilized to give cohesion or to reduce the permeability soils. Portlant cement grouting was performed first and micro cement was then grouted through the upsteam portion of the dam. After the permeation grouting consecution, seepage quantity trend of the earth-fill dam was stable and dependent on the reservoir level, and defected dam was effectively repaired. The permeation grouting application significantly reduced leakage to 4≈50 m³/day compared with initial damaged stage of 2500m³/day and compaction grouting of 800m³/day application. The seepage quantity significantly reduced from 640 m³/day to 4.1m³/day after applying the permeation grouting method, and the leakage decreased from 2,500 m³/day to 800 m³/day.