We often take the stability of the ground under our feet for granted, but it only takes one good rain storm to show what water does to soil stabilization in hillsides, roads, and gardens.

Types of Soil

Rock soil comes in different granular sizes, from silt to boulders. Silt is fine-grained soil that feels like talcum powder. Sand is a little larger and can vary from soft grains filtering through an hour-glass to rather coarse grains that hurt to walk on with bare feet.

Then, there are gravels ranging from smooth, round stones called pea gravel to one-inch or so pieces of broken stone. Between these is crushed granite, which is often spread along dirt roads to keep the dust down. The stones in crushed granite lock together when a vehicle runs over them, binding the surface and providing a permeable, yet firm surface that won't erode or become as rutted as hardpan roads.

We often think of boulders as being huge monoliths the size of cars. Actually, a boulder can be as small as two or three inches. These are called river rocks.

Uses for These Soils

If you have a flat area where people play games, soil made up of silt or sand works well. Silt often needs to be dampened to keep dust down. Sand is a great play surface unless it's a game that requires fast running. Silty soils can be tamped down to create a hardpan surface.

As noted above, gravels are good for roads, driveways, walkways, and even some playgrounds. Children can play on pea gravel without getting scraped up, yet it's durable enough to withstand years of use. Coarser gravels can be effective in traffic areas because the stones shift and lock under the pressing action of vehicles. One-inch gravels also provide good erosion protection on inclined driveways, especially if the under-surface is hardpan. Gravel upon sand washes away more easily.

For steep hillsides, river rock, like stones you'll find in streambeds, can be stacked against the incline to keep it from eroding. These are especially good because they aren't as easily washed away in a heavy rainstorm.

It's a good idea to observe where erosion is happening before choosing soils. Repairing a washed-out ditch with silt won't work as well as using river rock or coarse gravel. The speed of running water determines what kind of soil you will need to stabilize the area.