The Sheepsfoot Roller
A humble herd of sheep was the inspiration behind this amazing piece of construction equipment.
During the 19th century, when building roads, a smooth-wheeled roller was the go-to piece of construction equipment. This roller worked well in sandy soil but as soon as they came to clay, the machine would fail horribly.
In 1900, John Fitzgerald noted how well a pavement in California was compacted after a herd of sheep marched over it. He saw that the sheep’s feet actually kneaded the clay instead of just pressing it. Soon after seeing this, he went to work designing a new form for roller by putting spikes onto a steel drum.
And in 1906 he patented his device.
Named the “Sheepsfoot Roller”, this machine with its spikes was quite popular until a Los Angeles contractor, H W Roll, revised the original design while compacting a major earth fill of a dam in 1927. There was only one major change to the machine and that was the spikes that were now designed into more of a ball shape. This roller had 120 balls at 20 cm intervals and weighed about 4 tons and these rollers were all pulled by a tractor. In 1933, as the sheepsfoot roller was used more extensively for soil compaction, it was further developed by a Los Angeles engineer named, Ralph R Proctor.
Today, this monstrous piece of construction equipment has come a long way and has got to be one of the more unique pieces of equipment on any building site. The one difference between the mainstream roller and the sheepsfoot roller are the bumps or knobs on the one. When making roads, usually both the sheepsfoot and the smooth roller are used for compacting the soil in preparation. Sheepsfoot rollers are also used in the making of dams, embankments, pavements and railroad construction.
You have a choice today of a self-propelled sheepsfoot roller or one that is dragged behind other equipment. Some of these varieties also vibrate for increased compaction. You can even get a small sheepsfoot roller that is hand-drawn. The size of the “foot” may also vary depending on what type of soil you wish to compact. The weight of the drums can be increased by ballasting with water or wet sand.
How it Works
The protrusions on the drums of the sheepsfoot roller work through the top lift and then compact the lift below. As the protrusion on the drum comes out of the soil, it will kick up or fluff up the material thus leaving a loose layer of soil on top. As more fill is spread, the top layer will again be lifted and the previous layer will again be compacted. This compactor works by compacting soil from the bottom up. There is one absolute benefit of using the sheepsfoot roller. The whole process of the top lift of soil always being fluffed, helps to aerate and dry out wet clay and silts.