Sub-base is the critical backbone that supports any surface, so it stands to reason that the selection of this material is important. The purpose of sub-base is to handle whatever the surfacing can't, making any necessary adjustments beneath the surface while still providing the consistent stability it requires. This why the selection of the proper sub-base material is so crucial to the overall project.
The use of 3/4" crushed aggregate rock, also referred to as angular rock, differentiates it by size and shape, so it's not like pea gravel or tumbled round river rock. Neither of those will remain in position as well as crushed angular rock, specifically 3/4 crushed (not 3/4-minus, class 2 permeable, pea gravel or any smooth and rounded stones), which can also be compacted. We'll get more into the compaction process within the drainage or sub-base installation page.
Did you know that concrete and bituminous asphalt are both permeable? Water does pass through them under what's termed hydraulic pressure, albeit very slowly and gradually. The most widely used sub-base over the past 40-50 years has been what's called class 2 permeable, used under pretty much everywhere we drive or walk on solid surfaces. The problem with class 2 is it's comprised of 50% to 60% of what are termed "fines" of a sieve size about the size of coarse sand or smaller, which can be washed out with water flow, compromising all of the larger rocks alongside it and eliminating the support for the surface.
Our founder was told by a Dept. of Transportation official that he had identified the number one problem with every road, highway or freeway built in the last 40-50 years, the use of class 2 permeable sub-base. He ended up conducting a seminar for the American Society of Landscape Architects (ASLA) annual convention all about the correlation between sub-bases and sinkholes.