For starters, the soil under the gravel driveway must be well-drained and strong. It also must be free of any organic material like sticks, tree roots and leaves or grass. All topsoil must be stripped off the driveway location and stockpiled for use at some other place on your lot. It is a very bad practice to build a driveway on top of spongy topsoil filled with organic debris.
In our case it is strong as we left the builder installed material in place. Over the course of 10-years it was packed down well. I had to dig some of it out at the concrete aprons so we could get a good transition. It was a good thing I have a toothbar on my loader as the original stuff took some doing to crack through. Any organic material was removed.
Water is the enemy of gravel driveways and any roadway. Surface water can erode the gravel off the surface of the driveway and subsurface water can turn strong subsoil into a quagmire. The weight of cars and trucks pressing down on a gravel driveway is not much different than the powerful hydraulic pressure used on construction machinery, car lifts and any other machine that uses the leveraged force of hydraulics.
The mud bog issue we had was due to the driveways being at the same level as surrounding yard. This allowed dirt to wash over the driveway making it a mess to drive and walk on in winter.
Water that is forced under pressure under the gravel can transport silt from the subsoil into the gravel. As the silt squeezes between individual pieces of gravel, it causes the friction bonds between individual pieces of gravel to weaken. When this happens, your gravel driveway can fall apart in no time.
It is often a great idea to install a geotextile fabric on top of the subsoil before the first layer of gravel is installed. This fabric prevents the silt in the subsoil from fouling the gravel. These products come in wide rolls and can easily be installed by two people who just unroll the fabric allowing it to lay on the soil. On windy days it needs to be covered quickly with a 4 or 6-inch-thick layer of crushed gravel. If you don't do this, the fabric might end up on your neighbor's lot.
We thought about adding fabric; but didn't due to cost considerations.
The first layer of crushed gravel needs to be a larger-sized gravel. Try to locate stones that are the size of baseballs or even softballs. Never use gravel that is rounded as each piece can move easily when pressure is applied to it. Angular gravel interlocks with adjacent pieces and the combined mass can act as on larger piece of rock.
Add additional layers of crushed rock in 4-inch thick layers with each layer being a smaller sized stone. Compact each layer with a mechanical roller or tamping machine. The final layer of gravel should have pieces of angular stone no larger than a golf ball, with many of the stones being the size of marbles. If you can install 10 - 12 inches of gravel on top of the geotextile fabric, you should have a gravel driveway that will last decades.
Since we only went 3" deep on the gravel, we chose the 1" x 3/4" rock versus the 1-1/2" x 3/4" rock. In hindsight, I think we should have ordered a 50-50 mix of both types.
Be sure the gravel driveway has a crown in it. This means the center of the driveway is always higher than the two edges. The crown allows water to flow off to the sides of the driveway preventing any ponding of water on the gravel surface.
Gravel driveways need some periodic care in the form of grading or dressing. Low spots need to be filled with gravel scraped from any high spots. If your driveway has curves, you will discover that car and truck traffic tends to push loose gravel to the outer edges of the curves. This gravel needs to be brought back to the center and inner part of the curves.
Any driveway will need maintenance, which we know. Asphalt and poured concrete were out of the question due to cost, and how they react with our expansive soils.
Gravel driveways built on hillsides need ditches on the high side of the driveway. These ditches capture surface water that runs down the hill and otherwise would run across the driveway. Larger angular rocks should be placed in the ditch to slow down the speed of the running water in the ditch. Monitor the ditch to ensure the running water is not cutting too deep a channel or eroding the ditch causing failure of the gravel driveway.
Fortunately our driveways are on fairly flat ground with any slope running more or less parallel with the slope.
OPTION 2 - The build up should go as follows - the first layer will be #3 stone (fist size); the second will be #57(little less than ping pong ball); and the final will be #21-A, or called crusher run (thumb nail sized stone with stone dust mixed in with it).
I like how each part of the country has different designations for stuff.
With a layered set up like this, you will have a driveway that will last many, many years.
Build A Gravel Driveway
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