Part 1 summarized rockfill placement and compaction guidelines for mine structures, including dams and structure foundations. Part 2 provided an historical perspective to rockfill dam construction. Part 3 for this article defines rockfill versus earthfill materials. The terms “rockfill” and “earthfill” are commonly used in the geotechnical engineering profession, but the transition between the two types of fill, to this author's knowledge, has not been accurately defined to the present day.
An earthfill material with various mixtures of clay, silt, sand or fine-grained gravel sizes is well defined by the Unified Soil Classification System (ASTM D-2487-00). As larger sized rock fragments are added to an earthfill, at some point the “earthfill” becomes a “rockfill” with predominantly coarse-grained gravel, cobble and boulder sized rock fragments. A review of past rockfill definitions and suggested upper and lower rock fragment size boundary limits are presented in this article for compacted rockfills.
