General Gravel Driveway Information
-Gravel layers should be at least 3"-8" thick
-Gravel driveway surface should be crowned or sloped to a bank.
Ideal Grade Percentage 2-5% Minimum 1% Maximum 11%
Calculate Grade Percentage: Difference in Elevation in feet divided by horizontal length in feet x 100
Example: 12' wide driveway, crowned at center, from driveway center to driveway shoulder is 6', assume there is a 2" difference in elevation between the center and shoulder. 2" converted to feet is .166 divided by 6 = .0276 x 100 = 2.76%
-After a rainfall event water should shed off gravel surface quickly and not flow down gravel. The turf or soil surrounding the driveway should be at a lower grade than the driveway. By keeping the water off, potholes and wash-outs are prevented.
-After installation of gravel, compaction is very important, a heavy roller, truck tires, vibrating roller or plate compactor should be used.
Calculating Driveway Gravel
Length in feet x Width in feet x desired gravel thickness in feet divided by 27 equals cubic yards. To convert cubic yards to tons figure 1.4 tons per yard.
To convert inches to feet use this chart:
1" = .083' 2" = .166' 3" = .250' 4" = .333' 5" = .416' 6" = .5'
7" = .583' 8" = .667' 9" = .75' 10" = .833' 11" = .916 12" = 1'
Example: A homeowner desires a 3" cap of Crushed Asphalt Gravel over his existing driveway, his driveway dimensions are: 100' long by 12' wide. 100 x 12 x .250' = 300 divided by 27 = 11.11 Cubic Yards or 15.55 Tons (11.11 x 1.4 = 15.55)
Remember to figure compaction of gravel: Calculated gravel needed + 4% (Using the above example (11.11 x 1.04 or 15.55 x 1.04), the homeowner should order 11.55 Cubic Yards or 16.172 Tons
Gravel Driveway Grading
Grading your driveway is an important part of proper gravel driveway maintenance. The process is started by loosening the hard packed gravel. This can be done with a scraper blade, a box scraper with ripper shanks or any other method to scarify the gravel. Any gravel that has been moved off the driveway into turf areas by snow plowing should be re-captured at this time. The gravel driveway must be loosened to the depths of potholes or else they will reappear. Gravel should be scraped from the edges to the center first, this creates a crown and then feathered out lightly to the edges of the gravel driveway. After the final grade is created it is important to pack the gravel, this can be done with vehicle tires or a heavy roller.
Common Gravel Driveway Issues & Solutions
Mud - Muddy Driveways usually have water issues. Improper drainage and grading is usually the cause. The problem can also be caused by improper driveway installation, the topsoil may have not been removed before gravel was placed or there may not be enough gravel at all. Make sure the driveway is higher than the surrounding areas. Remove topsoil if present and add gravel.
Clay - Driveways that are placed on clay usually have soft spots. At wet times of the year the driveway may feel spongy or act like a trampoline, when you drive over the gravel you can see the ground move this is called rebound. Driveways that are constructed on clay should have 12"-16" of clay removed and 8" of fill sand placed with at least 6" of gravel. Another solution is to place a 4-6" layer of 2" rock between the clay and your driveway gravel, this will help lock up to prevent "rebound".
Sand - If there is not enough gravel on the driveway fine sand may mix causing deep tire tracks each time the surface is driven over. Grade the driveway to a crown or slope and install at least 4" of gravel.
Standing Water - Driveway is the lowest point of the landscape, add gravel or remove birm so water will shed off. Sometimes installing a small swale along the driveway on one side or both will remedy the water issue.
Birm - Birm is a build up of soil, sod or gravel along the edges of the gravel driveway. This build up makes a mini dam that holds water on the gravel surface not allowing the water to shed off. This is the most common problem for gravel driveways but it is the easiest and most affordable to fix. Simply remove this build up and you'll see a big difference in the quality of your driveway.
Wash Boarding & Potholes - First check for birm, make sure the water can flow off the driveway. Regrade the driveway, make sure to scarify the gravel to depth of the potholes, this is the only way to get rid of them. Simply filling in the potholes with new gravel will not work. After grading add gravel over the entire surface if necessary to correct low areas.
Incorrect Gravel - Stone that is round should not be used as packing gravel. Also stone that has all uniform particles is not proper driveway gravel. Correct gravel has packing dust along with irregular edges that bind together to make a solid driving surface.
Water Flowing Over Gravel - Wash outs occur when water flows over gravel. If large volumes of water continue to be a problem, a culvert should be installed so that water can move through without disturbing the gravel. A swale or ditch could also solve the problem.
Check dams - Check dams are mini stone dams that run perpendicular to the flow of water inside a swale or ditch. Usually made of large stone or temporarily made of straw bales. These dams help slow the flow of water down a steep slope to prevent erosion.
Rip Rap - This large 6-12" rock is used prevent erosion on slopes where water is flowing down. Used where water is channelizing and changing grades.
Geo-Textile Fabric - A fabric that is rolled out between the sub-grade and the gravel layer. This fabric helps stabilize the gravel making it more stable and suited for high traffic or heavy vehicles. This fabric should also be used when installing rip rap, check dams and over wet soil conditions.