Bryant RedHawk wrote:Sand does not make a good footing substrate, since it can shift or compress.
If you look at bridges, they like to remove all sand and gravels before building the towers, the Brooklyn Bride has one tower, now leaning, build on a sand base because they couldn't get down to bedrock.
Rufus Laggren wrote:
...FWIW regarding drainage. I have read one engineer who designed fill and engineered drainage for big dams and road beds in the 60's claim that concrete sand (what is used to mix concrete) performed far better than any other fill for drainage. He returned to projects 20 and 30 years later and made a point of checking whether his fill has remained stable and continued to perform to direct moving subsurface water properly. He views gravel/crusher-run as a special purpose fill that is grossly overused. Cement sand is spec'd to have sharp angles and corners just like crusher-run; both are spec'd for load bearing structural purposes because the particles tend to lock and hold together better than smooth sand or rock; the sharp irregular pieces also allow excellent drainage. But the reason he prefers sand for drainage is that it does not "silt up" as much from the surrounding earth diffusing into it. I don't know all the science but apparently the relative size of the particles in each kind of earth or fill has a huge influence on whether on not the boundary between to two types remain open to water flow over time. Gravel boundaries with earth tend to silt up as the earth migrates into the relatively large gaps in the gravel and pack hard; the sand being more the same size particle, doesn't offer easy pathways for the earth, clay or mud to move into and pack and so the boundary remains relatively free flowing.
Bryant RedHawk wrote:That engineer was referring to "sharp" sand