My area consists of mostly a clay mix soil. For a patio or driveway we will excavate a few inches of topsoil followed by sticky clay. It seems like this clay is pretty hard and a stable enough base for a patio. The fact is that when water is introduced it is a slimy mess and will squeeze different directions to escape pressure. Having a heavy paver system place on top of it can lead to failure over the years.
Every Hardscape Jumping Jack Vibratory Rammer contractor has a vibratory plate to compact the base and set pavers into sand. The problem is this type of compactor is not sufficient for the sub soil. A vibratory compactor does just that, vibrates. It exerts a a low amplitude and high frequency. Most range from 1500-5500 Hz. On Grade 8 gravel and other base materials is shakes the stone to fit into each other through the many small hits it produces. Clay is not angular like the base stone and will not settle into itself through vibrations.
A rammer or jumping jack type compactor is what should be used to compact clay. Rammers use low frequency(700-2300Hz) and high stroke blows to compact material through force. It is like taking a sledge hammer and smashing it into the clay compare to a plate compactor which just drops a small weight many times.By using a rammer in clay type soil you are essentially beating the trapped air and moisture out of the soil. You will see the ground drop an inch or two after ramming. You might even see water come to the surface.
Most contractors in my area do no compaction of the soil before putting in a patio or even driveway. I see paver systems that have failed all the time due to improper soil preparation. Most likely you will not see it in the first couple of years but eventually you will. Areas where you see it the most are around the perimeter of the house 3-4 feet out. After the house is built the foundation is backfilled with chunks of excavated clay. There is all kinds of air pockets when the backfill and they do not compact. 6 months later a Hardscape contractor comes by to put in a patio or driveway and does not compact this soil either. After a rotation of seasons you will see that 3-4 ft band sinking. If the contractor took the extra step to compact the soil this problem would not have occurred. But back they come to perform warranty work.
Yes a rammer can be an expensive tool but in the long run saves you warranty costs and keeps you customers and you image happy. I even use the fact that we compact the soil as a selling point. Most homeowners don’t know much of a paving system and are happy to get a quick education on it. This gives you the opportunity to show why you are different and why your paver system might cost more then the other guys.