Chapter 9: Earthfill dams

Early earthfill dams were often of homogeneous construction and have a poor safety record. This method of construction is not recommended for dams more than a few metres high. Many later earthfill dams were built with puddle clay cores and filters.

Chapter 9 recommends that, for earthfill dams in general, but particularly for those in seismic areas, it is important that filters be able to deform without leaving open cracks. Open cracks are most likely in the upper part of a dam, where there is little overburden pressure to help close them. Therefore, filters should not contain more than 5% fines, in place after compaction, because fines promote capillary tension that could help cracks remain open in partially saturated filters.

Filters should also not contain binding or cementing agents (such as salts on particle surfaces) or more than 3% mica, which readily breaks down into fines. Even microbes, notably iron-fixing bacteria, have been found to act as binding agents. Filters and gravel drainage zones should not be made too loose, so that they would be liquefiable, or too dense. A higher density increases the potential for brittle behaviour and cracking.