Given the fact of Global Warming and the very large probability of
significant future sea-level rise, it should be obvious that a number of
coastal cities will have to be abandoned, which means their
populations
will need to move inland. Sounds like an excellent opportunity to plan
some new
cities, from the underground up.
Having selected some likely terrain, the city planners would decide
where
the main roads should go, and mark the ground accordingly. We now
start digging them up, nice deep trenches, say 15 meters. All the
trenches are thoroughly sealed against the water table, if present. We
now put a roof over the bottom 4-meter space, with numerous suitable
access points.
In that space, in the future (as buildings get built), we will put conduits
for
such things as sewer lines, water lines, power lines, gas lines,
communications lines,
and so on. The conduits should be sealed so that the remaining space
can double as a storm-drain system. Note that when the storm water is
pumped out, it could be filtered and considered part of the city's
overall water-reservoir system. The conduits should also be
organized such that appropriately designed service vehicles can drive
through these pathways, so service personnel can easily reach specific
locations for such things as installing connection points for future
customers.
In the space above that level, we plan for a subway/metro transport
system. We don't need to think about actually putting such a system in
there until the population of the city is large enough to need it, but
having the space ready in advance, to prevent major traffic
interruptions
that happen in any ordinary unplanned city, is a good idea.
Also, like the London Underground in WW2, this level might be suited
for
emergency sheltering of the population.
Above the transport level we have another roof, this one heavy-duty
enough to support the dirt that we will put back into the trench, plus the
roadway that will eventually be built, plus all the vehicles that will
eventually occupy that roadway. Likely, to be strong enough to resist
that,
it will also be strong enough to resist the atmospheric overpressure
associated with an air-burst nuclear explosion (see above about
sheltering the
population).
As buildings get built, relatively small/short trenches or tunnels need to
be dug to
connect to the main Infrastructure Infrastructure tunnel system.