Most types of stone are stronger than asphalt and concrete. It would make sense that when carving out of a tunnel, the stone on the bottom surface can remain there and become the road to drive on. It would also be cheaper, as less work has to be done. Why is this never done, or are there examples that I don't know of?
If you ever drove on cobblestone, you know how it feels. Advantage of concrete and asphalt is that they can be made very smooth over significant areas without extreme effort. I am having a hard time trying to envision similar quality cut of natural stone.
Quote from: kalvado on May 13, 2019, 08:14:41 AM
If you ever drove on cobblestone, you know how it feels. Advantage of concrete and asphalt is that they can be made very smooth over significant areas without extreme effort. I am having a hard time trying to envision similar quality cut of natural stone.
Plus, of course, cost. "Extreme effort" surely equals "extreme cost."
- A solid stone surface would have questionable friction to begin with, and would become polished quickly. Friction is a factor in concrete and asphalt concrete designs.
- You'd have to be be very deliberate with carving the crossfall of the driving surface. Building a pavement structure with crossfall is much easier.
- Any damage to the driving surface would have to be repaired using asphalt or concrete, not sure how well that would bond in order to fill in the crack/hole. So you're into further carving.
- No option to run utilities under the highway or cut loops in the surface.
Low volume secondary roads with 50 AADT or less work well with a crushed stone surface.
Typically about 4 to 6 inches depth of Aggregate Base 21A grade stone which is a processed material derived from stone mined from a quarry.
Quote from: Beltway on May 13, 2019, 11:16:23 AM
Low volume secondary roads with 50 AADT or less work well with a crushed stone surface.
Which literally no one asked about.
Quote from: MNHighwayMan on May 13, 2019, 11:19:03 AM
Quote from: Beltway on May 13, 2019, 11:16:23 AM
Low volume secondary roads with 50 AADT or less work well with a crushed stone surface.
Which literally no one asked about.
It didn't specify any particular highway system.
Are river rocks considered "natural stone"? I've driven on plenty of roads paved with river rocks in Mexico.
Quote from: Beltway on May 13, 2019, 01:34:42 PM
Quote from: MNHighwayMan on May 13, 2019, 11:19:03 AM
Quote from: Beltway on May 13, 2019, 11:16:23 AM
Low volume secondary roads with 50 AADT or less work well with a crushed stone surface.
Which literally no one asked about.
It didn't specify any particular highway system.
No, not the traffic part, the "crushed stone" part. Everyone knows that crushed stone is used for low-volume roads. The question was about using existing stone strata instead of any sort of paving material.
I don't think natural stone is as nice of a material as you might think. There are all sort of irregularities between layers, not to mention all the other reasons previously mentioned.
As cbeach alluded to, too smooth of stone (which a "natural stone surface" would also eventually wear down to) means less friction and vehicles sliding off the road.
As csw alluded too, too irregular of stone shape, or too coarse of stone and you have sharp edges resulting in tire punctures. This has occasionally happened in locations where the local crew used too coarse of an aggregate on the roadway.
Related: polished surfaces on sidewalks are the worst thing ever conceived by man. Even worse when it's raining and those polished sidewalk tiles are slippy...and they are at an incline that requires shorter steps.
Guanajuato in mexico has a series of underground roadways that were previously rivers. They are stone.
(https://assets.blog.slice.ca/imageserve/wp-content/uploads/sites/5/2014/12/b7f367cb645260f02712f3f581f7dd88/x.jpg)
It is on Streetview but the images are useless
Might be the only place in the world where the user submitted images are better
https://goo.gl/maps/rE7U2Ec88bvicLGa6
Quote from: jamess on May 14, 2019, 04:25:35 PM
Guanajuato in mexico has a series of underground roadways that were previously rivers. They are stone.
(https://assets.blog.slice.ca/imageserve/wp-content/uploads/sites/5/2014/12/b7f367cb645260f02712f3f581f7dd88/x.jpg)
It is on Streetview but the images are useless
Might be the only place in the world where the user submitted images are better
https://goo.gl/maps/rE7U2Ec88bvicLGa6
Looking at the moisture on the walls (and along segments of the bottom "pavement"), it seems like at least an even chance these tunnels could again become rivers at some point. Also -- with anything except exceptionally bright lighting, these narrow passages might (and, to me would) become claustrophobic! Given the options, I'd personally stay out of them!
Quote from: jamess on May 14, 2019, 04:25:35 PM
Guanajuato in mexico has a series of underground roadways that were previously rivers. They are stone.
But it's clearly not a natural stone surface, as the OP was asking about.
That is a very interesting design though.