We have all played with dirt and sand. Most of us can recall the first time we played with dirt and world of possibilities it opened. Suddenly we could “build” castles, highways, cities…
But if you are like me, those possibilities quickly came to a halt when water evaporated and the soil or sand became dry and lost its shape.
So you can image my thoughts when I saw a video claiming he’d “Engineered” dirt to support the weight of a car. Really? How can this be? What type of black-magic is this?
Dirt/sand, by themselves, are unstable building materials because of the infinite number of friction planes they have. Friction is what keeps materials stable. And controlling the direction of that friction is what allows us to build.
While dirt/sand can maintain shallow “Pyramid” shapes, anything steeper causes the dirt/sand to slide off. You an prevent this by adding horizontal forces to help it keep its shape and grow taller.
Or, you can engineer the dirt/sand by controlling the frictions within. As demonstrated in the video, by simply adding sheets of paper towels to a dirt pyramid, you can help it support vertical forces. Similarly, you can engineer dirt to support a vehicle by mixing sheets of fiberglass window screen to reinforce it and limit its horizontal friction planes.
It turns out this achievement is all over our highway systems. We just never paid attention. No black-magic, simple engineering.
