Analyzing the effect of defect in the upstream impervious blanket on the seepage behavior of earthfill dam

This paper aims to thoroughly investigate the effect of weakness in the upstream impervious blanket of earthfill dam on the seepage behavior. For this end, a limited zone with high permeability is considered in various situations of impervious blanket. Then, for each situation, the discharge value and seepage pattern through the foundation is determined by performing 2D finite element seepage analysis via GeoStudio software. Regarding to the analysis result, the location defected zone in upstream impervious blanket directly influences the seepage pattern through dam body and foundation. If the defected zone is occurred in the situations close to the dam core, escaping water from weakness zone of impervious blanket impact the clay core water tightening performance and water potential head drop is not completely occurred in clay core. From the erosion potential view, the critical condition is directly depended on the foundation permeability. For most permeable foundation, the gradient of 5.6 is recorded for the defected zone located out of dam body in defected zone. For this type of dam, the gradient in foundation is insignificant. If the foundation has lower permeability and defected zone is occurred in impervious blanket next to clay core connection point, the foundation beneath the defected zone is susceptible to erosion.