Concentrated leaks at core-filter interfaces in earth dams increase erodibility of soils, which may lead to catastrophic failures. In this paper, a mathematical method is suggested to determine the self-healing nature of these leaks, which considers the erodibility of base soils and the pore size characteristics of filter soils. This method is fundamentally different from the existing empirical methods in that it does not involve comparison of particle sizes of the base (D85) and filter (D15) soils. Instead, the method is based on the fundamental processes of particle transport and deposition phenomena. An advection-type equation is used with a deposition coefficient (l) to describe particle transport in filters. The nature of particle deposition at the interface, which is described by an exponential attenuation function with respect to distance, is used to infer the possibility of self-healing. Filters with a range of particle size distribution are examined to evaluate their self-healing potential and to appraise the criteria currently used in practice. The method suggests that the entire particle size distribution, and not mere D15, governs particle accumulation at the interface.
Extensive statistical data assembled by ICOLD (1983, 1995) on failures of earth dams reveal that 30 to 50 percent of accidents involved piping or inadequate drainage. The safety of embankment dams depends to a large extent on proper control of particle migration at core-filter interfaces. Piping is often initiated in a crack at the core-filter interface. Since there is no way to assure a priori that the core will not crack (in fact, evidence suggests cracking of core is common due to construction deficiencies, differential settlement, or seismic activities), the downstream filter is usually designed to prevent progressive piping through the core in the event of a concentrated leak.