Abstract:This article presents two typical examples of engineering geological problems in dykes with defects or in danger resulted from permeation through the underlying bed rock:fault-typed permeation at dyke foundation in Shijiao Section of Beijiang River Dyke and the resulted osmotic deformation,the covering type of karst dyke foundation permeation in the auxiliary dyke of Huangbizhuang Reservoir and the resulted large-scale collapse of the dyke body. It has been found in artificial isotopic tracing,natural tracing,in environment isotopic and water chemical analysis,and in the determination of ground layer density,that there is a severe water-permeating fault of NE strike in the underlying bed rock of Shijiao Section of Beijiang River Dyke,which is directly related to the dangers during the flood seasons for years. It has been further determined by applying the plane thermal source principle that this fault is basically flat and straight in space and is dipping to NW. Bed rock karst is the objective geological foundation of the collapse of the auxiliary dyke of Huangbizhuang Reservoir,and improper construction method for anti-permeation consolidation is the first direct inducing cause to the collapse.