Myths & Facts #6 Why filter is required for dam core?

In general, dam core consists of low permeable clayey material which is susceptible to long term settlement and subsequently produce translateral cracks across the core.

Seepage flow channels can be generated from the core cracks to cause internal erosion of fine materials. Therefore, chimney filter is usually installed on downstream side of the dam core to prevent the subsequent internal erosion of the fines along with providing a drainage path for the possible concentrated seepage leakages.

FEMA filter manual (2011) specifies three different filter design categories- retention, permeability and anti-segregation. The first two criteria are rooted from Terzaghi’s granular filter design whereas the last one was added to prevent the granular filter from self-segregation by limiting the gradation of filter.

In US territory, geotextile is not allowed to be used as a filter media within critical dam structure due to high risk of internal clogging and difficulty of the retrofitting. Granular filter feasible for its self-filtration process is only accepted as for the dam filter materials.?

Mechanism of the bridging process above granular filter was well explained from below video clip.

https://youtu.be/qsk641OhjcY