According to USACE

According to USACE (2004), the core width for an embankment should be established using seepage and piping considerations, types of material available for the core and shells, the filter design, and seismic considerations. The minimum core thickness is governed by the safety against piping or leakage. The minimum thickness for tolerable seepage loses and for proper compaction is depending on the type of construction material available and the design of transition at upstream and downstream of the core. If the available materials have high erosion and cracking resistance as well as high flexibility, smaller thickness of the core can be used from economic point of view.