Designing appropriate filter materials is as important as ensuring the safety factor of the entire body of earth dams. The performance of the downstream filter zone in earth dams could be significantly influenced by base soil features, particularly in the case of cohesive broadly graded cores. The effects of several variables, such as base soil plasticity, fine content, and clay content, on the properties of effective filter materials were investigated experimentally in the current study. Results obtained through the no erosion filter (NEF) test indicated that the plasticity of base soil materials had no apparent correlation with the corresponding filter materials. However, fine content was found to have significant effects on the boundaries of the no erosion filter, especially for soils classified as Group 1. Although there was a decreasing tendency in D15f size with increasing clay content of the base materials, the effects of clay content on the required filter materials were not as significant as those of fine content. In conclusion, designing filter materials by concurrently considering d85 and fine content (F) of base materials appears to be more logical than separately utilizing these effective parameters. In this scenario, the new filter design criterion was derived using regression techniques based on experimental results.
Vakili et al. (Tue,) studied this question.