Given that the sand of sand dunes are much finer and smoother than beach sand, how does Dubai/the UAE have so many things that seem to be built on them?
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It’s just impressive, given that whenever I try to stand on top of one, I sink and slide to the bottom and find it hard to balance. I can’t imagine what building on one is like, and I can’t find any videos or information on it—either beaches or flat desert, but not on sand dunes!
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Basically, I’m curious about the challenge and process for building on sand dunes, and would appreciate an explanation.
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Thanks in advance!
In: 1603
Piles and different foundation setups. There are many kinds you can use actually and correct one is down to what the engineers are experienced in and what the project needs.
But imagine you put two phonebooks together, so that the leafs are neatly laid from both sides evenly. The friction between two sheets of phone book paper is basically nothing, but if you multiply it by 1000, you get lots of friction. And this is how piles work. They are long and have lots of surface area against anything you push them in to, even soft sand. These prevent the foundations on top from moving sideways, or up or down. After this you can connect these to make a raft foundation. This setup is so solid and permanent after it’s natural settling that it can be considered to not move at all. Often you can find a sort of a strange hump near old building development, these were the foundations of the tower crane used for them. They don’t move, but the ground around it will move, so they can become quite pronounced. After the you lay a cast foundation on this all.
But now… How do you do this for something that doesn’t have “foundations” in the same traditional sense. Like a road; no one is driving piles for a road. Well here we start to utilise the natural properties of the ground, or sand in this case.
First you dig ditch, basically with 45 degree slopes on the sides (this is important). Then you place some special fabric at the bottom, fill a layer of sand, then another layer of fabric, another layer of sand… so on and so forth. You are basically creating sand and fabric sandwich composite.
Why fabric? It tends to be soft and fragile, what good does it do? Well consider something like a cotton blanket. Yeah it doesn’t really have shape it’ll compress if you put something on top of it, you can’t build up with it, if you tear it from the side it’ll rip apart. But here is the funky engineering, it doesn’t need to. That an average cotton dish towel, hold it perfectly so it is a plane, and now pull on it as hard as you can. You can’t rip it apart by evenly pulling it. The threads it is made of all share the load equally and therefor they all take very little of it. Anyway back to the sand layers. As we know from playing in a sandbox, loose sand is soft and it flows out under you if compressed. it is like liquid in a way. Right now, remember the properties of the dish rag? How you couldn’t pull it apart? Now lets combine these two. The fabric prevent the whole layered foundation from spreading, the sand prevents it all from compressing. So now you have a foundation that doesn’t want to really move made entirely from fabric and sand. On top of this you build your road. Last question remains: Why 45 degree slopes? Because triangle is the strongest shape, and 45 degrees has the properties of using least surface area (volume of sand or dirt) while having the greatest tringle properties. If you take a perfect square and cut diagonally from point to point, you get a triangle with 90 degree and 2 45 degree angles.
With these methods of piles, fabric, dirt and foundations, you can build anything on just about anything. You could basically even build on water in theory, in an ideal setup. But as we know cows in a frictionless vacuum don’t live for long.
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