Seepage barriers have been used extensively to mitigate seepage problems in dams and levees. Although the design of many of these dams and levees has been based on intact barriers, seepage barriers have been shown to be susceptible to deformation and cracking when high differential hydraulic pressures act across the barrier. Under certain conditions, these cracks can lead to serious seepage problems, which could potentially lead to the development of a low-resistance seepage pathway. Three scenarios have been identified where there is the potential for erosion to occur adjacent to a crack in a barrier: 1) erosion at the interface between a fine-grained soil and a course-grained soil, 2) erosion of overlying soil due to flow along a joint in bedrock, and 3) erosion of the barrier material. The objective of this study is to investigate the first mode of erosion and identify the conditions at which more serious seepage problems can develop. The research has been performed using a laboratory model to simulate conditions near a seepage barrier crack under the scenarios described above. The results from the laboratory testing were compared to finite element seepage models for each scenario to estimate the flow velocities near the crack. The flow velocities were compared to estimated critical velocities of the soil to assess where erosion is likely to occur. A comparison was made between the observed behavior in the model and the behavior predicted with the computer model. The results of the research will be used to develop a method to assess the potential for erosion to occur and develop into a failure mode based on conditions near seepage barrier cracks.;
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