Dear Tim: My new blacktop driveway is already falling apart. A heavy rain washed away the gravel on the edge of the driveway. As a result, the gravel under the new blacktop is starting to erode. Why is this happening? What is the best repair I can do so it never happens again? I’m handy and not afraid to work. Will your repair method stop soil erosion in other areas of my yard? — Sally C., Hartselle, Ala.
Sally: I’m sorry your new driveway is not holding up. The good news is you can restore it — and make it better if you follow my advice.
Erosion is a natural process. I studied geology in college and hiked to the bottom of the Grand Canyon on my first major field trip. I witnessed the power of running water over solid rock. Water and gravity are great partners when it comes to erosion!
I also studied physics. People often overlook Newton’s second law, which is expressed in the simple equation force equals mass multiplied by acceleration. Your driveway erosion illustrates this law perfectly.
To put it another way, think about how much energy it takes to move a grain of sand. You can move a simple dry grain of sand with a puff of your breath. Use the same amount of breath but aim it at a small angular rock about the size of a grape. Your breath will not budge this small stone.
Your contractor installed the wrong size gravel along the edge of your driveway. Moreover, the gravel must be the correct shape. Large pieces of angular stone require lots of energy or force to move them. In contrast, small pieces of round stone similar to ball bearings can be moved with a tiny amount of force.
The gravel on the edge of my own steep driveway used to erode with each moderate rainstorm. I replaced the small 3/4-inch pieces of gravel with three-inch stones. All of a sudden my problem disappeared!
At the present, my town’s roads suffer from the same problem. The road crews install small angular stones in the road shoulder. The gravel is eroded by the force of the car and truck tires on right-hand curves. In the long run, this erosion can be stopped by installing the same 3-inch interlocking angular rock I used on my driveway. Much more force is needed to dislodge these.
Without delay you need to install the larger pieces of stone. Install the stone a minimum of 6 inches deep by 12 inches wide. Small angular pieces of crushed stone can be used to fill the gaps between the larger stones.
Angular stone is available at local gravel pits. This stone is used beneath new roads built near your home. The gravel pit will deliver the stone to your home. You’ll need to calculate how many cubic yards of stone you’ll need.
By all means, make sure the large stone is about 1 inch below the top surface of your driveway. Lawn mowers, snowplows and string trimmers must not be able to kick up the stones.
On the negative side, you may not like the look of these larger stones. In that case, think about the anguish you’ll feel as soon as a car or truck drives along the edge of your driveway and a large crack appears in the blacktop. The large stones provide support to the edge of your blacktop.
You can stop soil erosion in your yard using the same method. Typically, soil erodes where water concentrates in small channels. With this in mind, make a hardscape feature in the channel. The rock will stop the erosion.
Fill the channel or rut in the yard with larger angular stone and line the feature with much larger rocks as you might see in a local stream. Take photographs of a few creeks or streams near your home. The photos will guide you as long as you pay attention to the overall look of the natural stream.
All things considered, I believe you’ll love the look of the large stones next to your driveway. Install about five or 10 feet of them, and then stand back 30 feet to look at your work. Colorful angular stones can be used to create an accent to your drive. Do your best to look at all the types of angular stone at the gravel pit and select one that you like.
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