You underestimate just how massive an undertaking tunnel construction represents.
Consider a thirty-foot tunnel with an interior seven feet wide and seven feet tall. That's enough for two lanes of foot traffic, but not big enough for any vehicles. For ease-of-calculation's sake, let's assume that the tunnel is a rectangular prism, and that the walls are all one foot thick. The exterior walls are going to be nine feet per side. Such a tunnel segment would require, at minimum, a little under 1,000 ft^3 of reinforced concrete.
Reinforced concrete runs around 150-160 lbs/ft^3, meaning such a segment would require about 75-80 tons of material. For thirty feet.
For reference, that would be basically two fully-loaded C-130Hs. For thirty. Feet.
And you'd need to divide them into at least eight pre-cast segments for a single segment to fit on a standard Army HEMTT, as they only have a payload capacity of about 10 tons.
Then there's the fact that the sheer weight of the materials means that you can't just slap them down and cover them with dirt. You've got to worry about compaction and subsidence. Meaning you need to excavate a far, far larger volume than you plan to use so you can lay down an adequate foundation. That or you can drive pilings down to the bedrock every few dozen feet to support your structure.
Reinforced tunnels are probably not going to be the solution for troops near the front. Or, indeed, for any position that is not going to be more-or-less permanent.
Beyond that though, there's a reason that the Army "treats excavation as something done with organic engineer equipment — backhoes, bulldozers, troops with shovels". Because that's the only way to do it. The geology at every site is different. Grade, soil composition, depth of bedrock, type of bedrock, depth of groundwater, all of these are relevant. You can't just deploy a TBM, turn it use, and expect to have a functional tunnel system. The Earth is not nearly that cooperative.
Lastly, consider the weight of material that you'd need to dispose of in constructing a tunnel. That thirty-foot tunnel segment? The walls may only be 1,000 ft^3, but the volume of material removed is closer to 7,300 ft^3. If that's dirt, which is maybe 80-90 lbs/ft^3, that's over 300 tons. If it's sand, which is closer to 100 lbs/ft^3, we're up to 365 tons. If it's rock, say an average sandstone, now we're up to maybe 125 lbs/ft^3, or around 450 tons.
What is the Army Corps of Engineers going to do with all of that?
Whatever the issue and challenge is, we need to protect our troops. The economics of it all is the challenge. Someone will always want to profit.
Love these disruptive thought processes.
You underestimate just how massive an undertaking tunnel construction represents.
Consider a thirty-foot tunnel with an interior seven feet wide and seven feet tall. That's enough for two lanes of foot traffic, but not big enough for any vehicles. For ease-of-calculation's sake, let's assume that the tunnel is a rectangular prism, and that the walls are all one foot thick. The exterior walls are going to be nine feet per side. Such a tunnel segment would require, at minimum, a little under 1,000 ft^3 of reinforced concrete.
Reinforced concrete runs around 150-160 lbs/ft^3, meaning such a segment would require about 75-80 tons of material. For thirty feet.
For reference, that would be basically two fully-loaded C-130Hs. For thirty. Feet.
And you'd need to divide them into at least eight pre-cast segments for a single segment to fit on a standard Army HEMTT, as they only have a payload capacity of about 10 tons.
Then there's the fact that the sheer weight of the materials means that you can't just slap them down and cover them with dirt. You've got to worry about compaction and subsidence. Meaning you need to excavate a far, far larger volume than you plan to use so you can lay down an adequate foundation. That or you can drive pilings down to the bedrock every few dozen feet to support your structure.
Reinforced tunnels are probably not going to be the solution for troops near the front. Or, indeed, for any position that is not going to be more-or-less permanent.
Beyond that though, there's a reason that the Army "treats excavation as something done with organic engineer equipment — backhoes, bulldozers, troops with shovels". Because that's the only way to do it. The geology at every site is different. Grade, soil composition, depth of bedrock, type of bedrock, depth of groundwater, all of these are relevant. You can't just deploy a TBM, turn it use, and expect to have a functional tunnel system. The Earth is not nearly that cooperative.
Lastly, consider the weight of material that you'd need to dispose of in constructing a tunnel. That thirty-foot tunnel segment? The walls may only be 1,000 ft^3, but the volume of material removed is closer to 7,300 ft^3. If that's dirt, which is maybe 80-90 lbs/ft^3, that's over 300 tons. If it's sand, which is closer to 100 lbs/ft^3, we're up to 365 tons. If it's rock, say an average sandstone, now we're up to maybe 125 lbs/ft^3, or around 450 tons.
What is the Army Corps of Engineers going to do with all of that?