The maximum particle size can be the same as the layer thickness. Some e.g. USBR (1991) prefer a maximum particle size 90% of the layer thickness.
c. Rockfill grading and limits on finer particles The rockfill grading may be further specified depending on the properties
required. Ideally rockfill is well graded, so it has a high density, strength and modulus after compaction and has a high permeability. However this is not always
Table 14.1 Examples of rockfill layer thickness.