When the guys at [Practical Engineering] say they have a dirty car stand, they really mean it! They made a block of dirt and sheets of fiberglass as reinforcement material, and the resistance was put to test by using it as a car stand. And yes, the block does the job without collapsing.
Soil is a naturally unstable material, it relies only on friction for structural stability, but it has a very low shear strength (the resistance of the material’s internal structure to slide against itself). Therefore, as soon as you put some weight, a soil structure fails. The trick is to form a composite by adding layers of a stiff material. Those layers increase the shear strength and you end up with an incredibly strong composite, or ‘mechanically stabilized earth‘ (MSE). You probably drive by some everyday, as in the picture at the right.
Even though the modern form of MSE was due to French engineer Sir Henri Vidal, reinforced soil has been used since the beginnings of human history, in fact, some sections of the Great Wall of China were made using this technique. [Practical Engineering] explanation and demonstration video is very well made, be sure to check it after the break. In case you don’t want to play with dirt next time you need to fix your car, you can always make a 3D printed jack.
19 thoughts on “A Car Stand Made Of Sand”
it goes back to before the great wall of china as well. there are sections of walls built in the deserts in isreal that have woven straw mats used in layers with earth to stabilize it. It’s commonly referred to geogrid in civil engineering circles and comes in during the design and construction of retaining walls and other steep slopes.
This is great! Seems like this would be very useful for anyone building a retaining wall in their DIY landscaping. Just layer landscape fabric every 6″ or so, or of course you could do screen like he did.
Best line: “I dropped this 25 lb barbell from about six feet up to simulate what would happen if you dropped a 25 lb weight on the cube from about six feet up.”
Normal dumping angel of sand is around 60°, wet sand even steeper.
If you put in between layers of grid or mesh to stop slipping you can build really high structures very easy.
Just a handful of cement or using an additional bag on the outside makes that perfect.
It’s about 35* and 45* for damp sand. Most bulk materials that have an angle of repose <=45*.
That’s why the “bent pyramid” exists in Egypt. The builders had not yet perfected their stone fitting skills to overcome gravity wanting to pull it down to a lower angle, as happened with another pyramid of much cruder construction.
Earthships have a similar form of construction, tires stacked and packed with earth. This gives great thermal stability.
Check out construction using rammed earth. If you remember the Galloping Gourmet, he was very involved in hand operated machines for rammed earth housing in Africa.
Er.. that’s cool but don’t ask me to change the oil with that holding it up. I’m sure it’s stable but um… I’ll just out that jack right back under thank you.
Don’t put the jack back under, put the car on a jackstand where it belongs! Working under hydraulics is a good way to get hurt.
A very interesting presentation. Do you think this method be adopted for building houses cheaply. Building walls with layers of MSE looks cheaper than using bricks.
From a materials cost perspective it’s definitely cheaper but since the MSE blocks aren’t stable to transport, you’d be assembling on site and that seems like it would be significantly more expensive.
Well, that can be debatable. For housing in developing countries, including disaster relief shelters, labor is plentiful/cheap (or even free if you have a displaced village population eager to have shelter). On the other hand, traditional building materials and transporting said materials can make up the majority of the total costs for these types of projects.
Many people of varying skill & abilities can be constructing MSE blocks on site simultaneously – no process flow bottlenecks due to limited tools etc. The fact that sand is the main ingredient is also a huge plus for these scenarios – its available in pretty much any region, reducing material transportation costs.
I wouldn’t be surprised if 10 MSE block huts could be built for the price of one wood or concrete hut in many resource limited regions
Heard from someone in the peace corps, that what you do is show locals how to build schoolhouse, community hall, well or whatever out of local materials, and hope they’ll spread the knowledge… but what actually happens is that when you leave the next village over gets jealous and raids them and drives them out overnight…. whereupon, even if those people who saw how to do it re-congregate in the now abandoned neighboring village… they will beg and whine for you to come back and build it all for them over again…
I get that he was a bit cynical about all this, but it occurs to me that “the locals” either being in great need for so long were in one of those states of disaster shock or acute stress disorders that make outside help in disaster areas an absolute necessity, it bucks up the afflicted. Just outsiders basically example setting pulls everyone together again.
Anywayyyy, just saying that any project of that type needs to bear in mind need for continual support and assistance, it’s not like you can come up with one wonderful simple idea and it will spread and fix the whole country/continent. You can build one house… and 10 years later go back and there’s that one house still, maybe with damage from people fighting over it. Seems like you need to keep building, like how you don’t stop an epidemic by injecting one or two people.
Seen the same on Indian reservations. The BIA builds them new houses, they move in and not only don’t take care of them they deliberately trash them. Asked some why they do that, “The government will build us new ones when these get bad enough.”
Yes if you had a huge 3D printer it could lay down the alternating layers of tensile and compressive materials to form the require metamaterial. You may still need an additional fixative to stop erosion that would otherwise compromise the structure of the material, then again you could just extrude a geopolymer mix and have something even better, even though there are essentually the same thing and it is the scale of the geometry that is different, well than and the fact that a geopolymer is reinforced in three dimensions rather than just layers.
If you are into materials porn you should check out this, http://materials.soa.utexas.edu/search/
Here is one very relevant entry, http://materials.soa.utexas.edu/search/materials/details/t/product/id/1827
A bit of an old video. I watched it quite a while ago. I have been noticing a lot as of late that I have watched a lot videos before they were posted on HaD. Although, it is an interesting video.
The retaining walls on those road ramps are not just for looks. They keep the fill in place in case of earthquakes and protect it from erosion.
When there’s room to spread it out, there isn’t a need for the walls because the fill can be allowed to assume its natural angle of repose so it won’t slump in a quake and plants can be used to protect against erosion, along with a mix of dirt and aggregate chosen to limit erosion.
Anybody have any examples of some inexpensive screen or mesh to do this on a larger scale? I could buy a lot of hardware cloth, but there may be a better resource for less money? I’d like to experiment with this on an Earthship that I’m building, but try to not use tires.
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