I'm more interested in the nuances of tunneling, like how they'll handle water seepage and flooding. Flooding is actually a huge problem with climate change causing larger and more frequent major weather events.
After Hurricane Sandy, it took almost a week to reopen the subway tunnels.
I can just imagine the kind of kinetic force that'll occur if a sled carrying a car slams into a section that has a few feet of water.
Airflow and humidity are other concerns. Airflow is necessary to keep passengers safe. Controlling humidity is important for keeping the infrastructure from degrading more quickly.
Any good paints or fabrics or metamaterials that could be used as a tunnel liner that only allow water to wick in one direction (from tunnel internals to surrounding soil)?
> it took almost a week to reopen the subway tunnels.
More like a few years collectively - a section of the G was closed every weekend for many months, the R was closed for a year, the L closes in 2019 for over a year.
This has just made me wonder what happens in emergencies or system failures. Are the tunnels wide enough to open your door or climb out a window? How far apart and numerous are emergency exit hatches? Is there off-grid emergency lighting (e.g. battery-backed)?
There would be few things more upsetting than your sled coming to a halt, inside a dark tunnel, and being unable to get out of your car. It would activate the same part of your brain that fears being buried alive.
Air isn't really a problem. A person breathes about .5 cubic meters of air per hour, so 100 people trapped for 6 hours will go through 300 cubic meters of air. The diameter of the tunnel being 14', that air supply would take up 68' of tunnel lengthwise. And that's one breath, the air can be breathed many times before the co2 level becomes too high.
The air inside the volume of a coffin can last you a few hours. Unless you are literally shoulder to shoulder with no other air, your oxygen will last as long as you need.
"The air inside the volume of a coffin can last you a few hours. Unless you are literally shoulder to shoulder with no other air, your oxygen will last as long as you need."
... unless there is a fire:
"Most drivers rolled up their windows and waited for rescue. The ventilation system in the tunnel drove toxic smoke back down the tunnel faster than anyone could run to safety. These fumes quickly filled the tunnel and caused vehicle engines to stall because of lack of oxygen. This included fire engines which, once affected, had to be abandoned by the firefighters. Many drivers near the blaze who attempted to leave their cars and seek refuge points were quickly overcome."[1]
In that case ventilation was the cause of those deaths, or at least made the situation worse. It doesn't have much to do with the availability of oxygen.
>Any good paints or fabrics or metamaterials that could be used as a tunnel liner that only allow water to wick in one direction (from tunnel internals to surrounding soil)?
Thermodynamically impossible without an input of energy. FWIW.
It turns out that most transportation tunnels do in fact have a significant input of energy.
Ventillation to exhaust waste heat is a major concern.
From discussions of net-zero housing in Alaska (Thorstein Chlupp), my understanding is that water tends to flow from hot to cold -- it will condense along a cold surface. A condenser + sump system where some engineering mechanism keeps the inner tunnel wall from remaining at equilibrium temperature with the interior, might work, though how cold that would need to be to keep humidity manageable would be a question. Routing the cold-side air ducts such that they waste heat to the subsurface and draw heat from the tunnel wall might be one approach. Further cooling through water (fresh, sea) is another possibility, though both present significant issues, scarcity of fresh in Los Angeles, and general nastiness of sea,
While you're right, in that heat is an issue in tunnels, harvesting low-temperature-delta energy is incredibly inefficient. It is always better to source the needed electricity from a generator that is specifically designed for such.
(The only time this may be untrue is when dealing with very small things like remote sensors, where running a wire might actually be more expensive than harvesting the microwatts needed locally. But this is a fraction of a fraction of a percent of total system needs.)
What I'm saying is that for the purposes of removing moisture, the temperature gradient itself is an energy flux which might be utilised.
In some ways, this is the inverse of an evaporative cooler, where the incoming air is saturated with moisture to lower its temperature before being vented to a warm space to be cooled ("swamp coolers" are best suited to dry climates, and have humidity issues). Here, instead, cool (possibly chilled) air could be ducted through the warm space, with the intent of condensing moisture onto the ductwork (for drainage by other means) prior to being vented into the space.
You're trading cooling capacity (condensing water warms the cold air supply) for humidity control.
I'm not trying to imply that this is practical, only that a latent energy flux might exist.
Something that can discriminate without energy input is a form of Maxwell's Demon. If you are unfamiliar, it's a lot of fun to learn about.
https://en.wikipedia.org/wiki/Maxwell%27s_demon is a reasonable start.
Check valves absolutely do consume energy. Something has to resist the spring forcing them closed, or they would never open. They are convenient in that their energy is sourced from the very thing they are controlling, but they are energy-consuming devices.
There's a Quartz piece about how Musk conceives all of his ventures that goes into some detail about the considerations behind The Boring Company, but the issue you mention is one of the ones where the technology still needs to advance, I believe.
After Hurricane Sandy, it took almost a week to reopen the subway tunnels.
I can just imagine the kind of kinetic force that'll occur if a sled carrying a car slams into a section that has a few feet of water.
Airflow and humidity are other concerns. Airflow is necessary to keep passengers safe. Controlling humidity is important for keeping the infrastructure from degrading more quickly.
Any good paints or fabrics or metamaterials that could be used as a tunnel liner that only allow water to wick in one direction (from tunnel internals to surrounding soil)?