Chapter 7: Seismic design of rockfill dams

In general, rockfill and earthfill dam types can be ranked in order of decreasing resistance to earthquakes as follows (USBR, 2015)

• concrete faced rockfill

• sloping upstream core earth and rockfill

• central core earth and rockfill

• earthfill with chimney and horizontal drains

• zoned earth-earth rockfill

• homogeneous earthfill

• upstream construction tailings and other hydraulic fill.

Chapter 7 discusses all aspects of rockfill dams, with particular emphasis on compaction, design of filters and the rare risk of liquefaction in the foundations. Slips, loss of freeboard and cracking of the core in earth core rockfill dams are risks that need to be quantified.

It is important to differentiate between the seismic response of rockfill and earth embankment dams, considering that compacted rockfill dams have an inherently high resistance to seismic loading. With modern construction techniques and gradation control, the materials that make up a rockfill dam have a high shear strength, high deformation modulus and high permeability, so this type of dam is less deformable and the possibility of generating excess pore pressure in an earthquake is very low. As a result, in general terms, a rockfill dam has a greater capacity to resist seismic excitation compared with an embankment dam.