I get that they’re layered with reinforced concrete but how is it that strong considering the walls aren’t even that thick?
In: 21
The power or arches! Engineers have been using arches for thousands of years to support way more weight than you would think is possible. Materials like concrete and stone are really good at handling compression. You can squeeze rocks with way more weight than the rock itself before it cracks. These same materials are also pretty bad at handling bending or pulling forces, and the explanation for that goes way beyond ELI5, but it has to do with how the molecules bond together on a microscopic scale.
What arches do is they redirect the weight of all the dirt above from bending into compression. The concrete at the top of the tunnel pushes against the concrete sloping down the side, which then pushes into the soil below the tunnel, resulting in the tunnel being evenly compressed. Since concrete is good at handling compression, it’s able to hold a lot of weight while remaining hollow inside.
[Quick reference pic](https://i.ytimg.com/vi/CdNYTjXJPKE/maxresdefault.jpg)
Latest Answers