Types of Earth dams
There are following types.
Rock fill earth dams
Rock fill dams are special types of earth dams that is made of cobble to boulder size rock fragments.
There is an internal concrete wall acting as the impervious barrier.
Earth rock dams
Earth rock dams are a hybrid that use rock fill shells and a compacted soil core.
For dams of medium to low height, these are made. The entire embankment is made of the same material. Low dams are always constructed as homogeneous dams. Because by making zones, cost will increase due to complication in construction.
In zoned dams, generally, the well drained materials such as sand, gravel etc., are placed in the outer shells whereas the clay soil is placed in the central zone. This will increase the water tightness of the dam. The shells provide main strength to the dam embankment.
Earth rock dam is an example of zoned dam. Their shells are filled with rock and central core is filled with compacted soil.
Fundamentals of soil mechanics by Dr. Aziz Akbar and M.Siddique Qureshi