Filtration design

$3.$ An earth dam is being constructed from a granular shell and a fine$-$grained core with the grain size distribution curves shown below. Sketch an allowable grain size region for a uniformly graded filter that is coarser than the fine grained core soil that will prevent the fine grained core soil from infiltrating into the filter using the criterion times of $D_{85,\text{c}\text{o}\text{r}\text{e}\text{,}},$ and is adequately permeable relative to the core using the criterion $D_{15,\text{f}\text{i}\text{l}\text{t}\text{e}\text{r}}>4-5$ times of $D_{15,\text{c}\text{o}\text{r}\text{c}\text{.}}.$ Based on the grain size distributions, do you anticipate that the filter particles might erode into the downstream shell? If so$,$ what would you do to solve this problem?