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hat are tough on braking sysems and engines, and suririsingly, for these vehicles, a engthy six to eight percent ^rade is called “severe.” This s not to say there are not realy steep roadways around, tomolo Place in San Francisco las a 32 percent grade: its sidewalks are steps, all the vay.
Do you know the grade of /our own driveway? It’s easy so measure, but will take two people. Take an eight-foot stud md rest one end on, say, the steepest part of your driveway. Make the stud horizontal and put a bubble level on it. Level Lhe stud. Next, take a tape measure and measure the drop from the end of the stud bottom side) to the driveway below.
What you read on the tape is the percent grade, but add one for 12 inches or more. You read eight irfehes; the grade is eight percent. You read 11 inches; it’s 11 percent. You read 15 inches; the grade is 16 percent. You read 23 inches; it’s a 24 percent grade.
Having selected a route, the next step is to build the driveway. The whole idea here is to beat water and handle the weight of traffic. It starts with bulldozing the sub grade (the earth) to get something with a good crown and camber. Usually, a 20-foot wide swath is needed for a good roadway, ditch to ditch. If red clay is the sub grade, you have a good start. Such soil does not accept water easily and by putting in a four percent camber on the earth any water will easily run off to the sides. The soil is then stabilized by bringing in loads of stone of various sizes to lay down the various courses to handle the weight of the vehicles expected to pass over the driveway. This stone on top of the sub grade makes up the subbase and/or the base course.
Small spaces between the stone, even after heavy compacting, lets any encroaching water drain off to the sides. Smaller stone (gravel), mixed with what are called “fines” or “dust,” make up the surface course, the idea here being to make the surface course as waterproof as possible, again to let water run off to the sides.
Where’s the water coming from? From rainfall and snow above, and from water rising through the ground by capillary action below. Both are trying to undermine your driveway. The spacing in the
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