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Let's just say that if the ground decides to give the puny adhoc steel structure is not going to pose much opposition. Forgetting for a moment how thin everyth

Let's just say that if the ground decides to give the puny adhoc steel structure is not going to pose much opposition. Forgetting for a moment how thin everything is, the arch only works if it is supported on the sides. It isn't, there is a bunch of space on both sides for the arch to get flat and give completely. But the structure may prevent full collapse. Also it is going to be relatively unlikely anybody gets hurt. It isn't like he is going to be sitting there 24/7.

indigomm 5y ago
The steel is only temporary. Of course one could argue any temporary structure should be up to scratch, but anyway it's not the final solution. He's building a tunnel within the steel structure and then filling the void with concrete.
- lmilcin 5y ago
  Well, that's what I understood from the last vid. But until then he is standing under structure that is definitely not safe. The trouble with these kinds of things is that everything looks fine until it doesn't. The way engineering solves these problems is through body of knowledge and experience in understanding of material properties and interaction of forces of both ground and the structure. The ground my start slipping slowly or it might decide to give in one go. It might happen after a particularly heavy rain or for no apparent reason at all. Unfortunately, I am not an expert in the type of ground he is facing. So either he is working with professionals (and hiding it to make the video more entertaining and in spirit of his other projects) or he isn't. In either case I think it is bad because it promotes the idea other people can do the same. Which is extremely dangerous in irresponsible to do on your own.
  - baremetal 5y ago
    what if i said i think its dangerous that you operate a car, and worse, you encourage others to drive cars when they see you driving a car.
    - indigomm 5y ago
      I find it quite refreshing that there aren't warnings not to try this at home. If people want to have a go, they will whether told to or not.
    - lmilcin 5y ago
      Engineers go through training to build safe tunnels and drivers go through training and exams to drive the car safely. Maybe you have heard, there are even rules that aim to making driving safer. Both tunnel collapses and car crashes happen, but but less because we have regulation to prevent most of the carnage. The correct analogy would be showing on youtube how fun it is to be driving car without any training or driving license.
Diggsey 5y ago
That's not how that works... Any granular material, even sand, will spread the forces laterally. It's impossible for the full weight of the soil above to be applied to the steel structure. The only reason you need the steel structure at all is to prevent it failing incrementally. Without it, the small amount of unsupported soil immediately above the tunnel can fall, which then leaves a gap for previously supported soil to move into, which can then itself fall, etc. until the whole tunnel comes down. The steel structure therefore only needs to preserve the shape of the soil. Finally, this is steel we're talking about - 3.5mm of steel in compression is still very strong. It's already massively overkill for the tiny amount of weight it actually has to support in this case.
- lmilcin 5y ago
  > That's not how that works... Any granular material, even sand, will spread the forces laterally. It's impossible for the full weight of the soil above to be applied to the steel structure. Absolutely false. The ground may be plastic on a long time scales (depends on the material) and over time full weight of it can be transferred to the structure. Do following thought experiment: build a bridge out of clay over a scale. The bridge might not suddenly collapse, but it will slowly deform and over time all weight of it will rest on the scale. If you have noticed, the top layers of the tunnel are made of clay. Clay is plastic and will creep over time. It is the same basic principle as buildings falling due to ground giving under foundations.
  - Diggsey 5y ago
    Even with a totally plastic material (which is a stretch, since there are certainly granular elements even in clay soil) the material will deform until it fills the gaps around the arch shape. At that point the material itself is forming an arch, and even clay has compressive strength since it has nowhere else to go. While it may increase the load on the steel, it's still a long way from having to support the full weight of the material above.

indigomm 5y ago

The steel is only temporary. Of course one could argue any temporary structure should be up to scratch, but anyway it's not the final solution. He's building a tunnel within the steel structure and then filling the void with concrete.

lmilcin 5y ago
Well, that's what I understood from the last vid. But until then he is standing under structure that is definitely not safe. The trouble with these kinds of things is that everything looks fine until it doesn't. The way engineering solves these problems is through body of knowledge and experience in understanding of material properties and interaction of forces of both ground and the structure. The ground my start slipping slowly or it might decide to give in one go. It might happen after a particularly heavy rain or for no apparent reason at all. Unfortunately, I am not an expert in the type of ground he is facing. So either he is working with professionals (and hiding it to make the video more entertaining and in spirit of his other projects) or he isn't. In either case I think it is bad because it promotes the idea other people can do the same. Which is extremely dangerous in irresponsible to do on your own.
- baremetal 5y ago
  what if i said i think its dangerous that you operate a car, and worse, you encourage others to drive cars when they see you driving a car.
  - indigomm 5y ago
    I find it quite refreshing that there aren't warnings not to try this at home. If people want to have a go, they will whether told to or not.
  - lmilcin 5y ago
    Engineers go through training to build safe tunnels and drivers go through training and exams to drive the car safely. Maybe you have heard, there are even rules that aim to making driving safer. Both tunnel collapses and car crashes happen, but but less because we have regulation to prevent most of the carnage. The correct analogy would be showing on youtube how fun it is to be driving car without any training or driving license.

Diggsey 5y ago

That's not how that works... Any granular material, even sand, will spread the forces laterally. It's impossible for the full weight of the soil above to be applied to the steel structure. The only reason you need the steel structure at all is to prevent it failing incrementally. Without it, the small amount of unsupported soil immediately above the tunnel can fall, which then leaves a gap for previously supported soil to move into, which can then itself fall, etc. until the whole tunnel comes down. The steel structure therefore only needs to preserve the shape of the soil. Finally, this is steel we're talking about - 3.5mm of steel in compression is still very strong. It's already massively overkill for the tiny amount of weight it actually has to support in this case.

lmilcin 5y ago
> That's not how that works... Any granular material, even sand, will spread the forces laterally. It's impossible for the full weight of the soil above to be applied to the steel structure. Absolutely false. The ground may be plastic on a long time scales (depends on the material) and over time full weight of it can be transferred to the structure. Do following thought experiment: build a bridge out of clay over a scale. The bridge might not suddenly collapse, but it will slowly deform and over time all weight of it will rest on the scale. If you have noticed, the top layers of the tunnel are made of clay. Clay is plastic and will creep over time. It is the same basic principle as buildings falling due to ground giving under foundations.
- Diggsey 5y ago
  Even with a totally plastic material (which is a stretch, since there are certainly granular elements even in clay soil) the material will deform until it fills the gaps around the arch shape. At that point the material itself is forming an arch, and even clay has compressive strength since it has nowhere else to go. While it may increase the load on the steel, it's still a long way from having to support the full weight of the material above.