Evaluation of remedial measures against foundation leakage problems of earth dams on pervious conglomerate strata: a case study

Abstract

This paper presents a case study on foundation seepage problems encountered at an earth dam over the last 55 years with various remediation efforts. The Pipasi Dam, 26.0 m in height, was built on a pervious foundation without any seepage control measures during its first phase construction. The geological conditions along with the leakages, remedial measures and the evaluation of the groundwater level measurements are presented. It is concluded that the past seepage problems within the dam foundation were caused by the geological condition. Neogene conglomerate outcrops in both abutments, and is overlaid by the relatively thin Quaternary deposit in the riverbed. Early treatments, such as the cutoff wall placed beneath the upstream toe and the upstream clay blanket, were only carried out in individual locations, and thus cannot form a continuous and complete spatial waterproofing system. The installed grouting curtain was regarded as a complete control measure. However, the initial design arrangement was changed during its actual installation, and also cannot form a closed-type one. In addition, the grouting effectiveness of the conglomerate is doubtful according to the check hole results, which reveal the loosened structures. As a result, hydraulic gradients and seepage amounts are still found to be higher than the expected level. Therefore, a secondary closed-type grouting curtain, which upwardly reaches into the dam body, should be installed into bedrock to eliminate future seepage problems. Meanwhile, regarding the spatial variation, the groutability of the conglomerate needs precise understanding as well.