Has anybody here built one, or seriously considered it then ruled it out for whatever reason?
I've always been interested in the idea of building a hidden shelter by having a large (10' or 12') culvert shallowly installed across a hillside. My area is steep and hilly enough that 50' or 100' of culvert could penetrate all the way from one side of a ridge to the other.
It seems appealing for the engineering simplicity/reliability and convenient access. Culverts seem like the state of the art in manmade caves -- we design them to handle not only soil loads, but also dynamic traffic loads on top and sometimes dynamic fluid loads inside in the case of storm drains. Collapse is a terrifying prospect for anything that you put soil on top of. Culverts and underground tanks seem like the best options for being engineered against collapse risks, but tanks with access only out the top have other major issues.
The amount of hiding you'd have to do to conceal 2 culvert ends seems tougher than a single bunker hatch, but easier than hiding a basement under a structure.
Cellars and bunkers typically have exits pretty close together, whereas a culvert through a hill would have its ends out of sight of one another, and be much easier to leave if something you wanted to get away from was messing with one end. A tank or bunker with a single entrance/exit is the worst case here -- if that access is blocked while you're inside, whether by a natural disaster or a hostile creature, you're stuck and at the mercy of people outside to remove the threat.
I also think a lot about emergency egress and airflow management. Silos, tanks, cellars, and some basements are pretty terrifying from an airflow perspective -- passively, they can fill with any sort of heavier-than-air gas, and if you go in and pass out you'll fall to the bottom. (even if the air is perfect in there and you have a medical emergency, extrication is still an issue) Then whoever is trying to get you out will have to go down into it as well, and lift you straight up from it to get you out, perhaps waiting on a ropes rescue team, rather than just walking out. Even carrying a patient up a set of narrow basement stairs is worse than walking out along a trail, as a culvert-as-bunker could offer.
The flood risk profile of a level culvert through a hillside is also vastly preferable to a basement, bunker, or tank. If it's downhill out both ends, hardly any water can accumulate inside before it simply flows downhill and away. Tanks, bunkers, and some basements are often watertight enough and positioned appropriately to hold large amounts of water if it gets in at all.
So, a culvert through a hillside, with exits on both sides of the hill, seems like an ideal underground structure for concealment, access, and safety. Basically a cave, but better, due to the lower risk of collapse. Yet I hardly ever see people discussing them as an option. This means I'm probably missing some important disadvantage of the idea. Why do you think people so widely prefer cellars, bunkers, even buried shipping containers or school buses, over culverts? Are they too expensive? Too specific about what terrain they're great in? Too conspicuous to install? Something else?
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Edit to add resource highlights from thread:
Edit to add comments which a forum member offered anonymously, and said they're ok with me paraphrasing in the public thread. They said they have done a similar project and found more cons than pros. They have found it very expensive once all the peripheral costs are factored in. They mentioned that due to future plans for the site, most of the culvert is covered by soil, but part of the surface is protected only by foam insulation for the time being.
Pros:
I've always been interested in the idea of building a hidden shelter by having a large (10' or 12') culvert shallowly installed across a hillside. My area is steep and hilly enough that 50' or 100' of culvert could penetrate all the way from one side of a ridge to the other.
It seems appealing for the engineering simplicity/reliability and convenient access. Culverts seem like the state of the art in manmade caves -- we design them to handle not only soil loads, but also dynamic traffic loads on top and sometimes dynamic fluid loads inside in the case of storm drains. Collapse is a terrifying prospect for anything that you put soil on top of. Culverts and underground tanks seem like the best options for being engineered against collapse risks, but tanks with access only out the top have other major issues.
The amount of hiding you'd have to do to conceal 2 culvert ends seems tougher than a single bunker hatch, but easier than hiding a basement under a structure.
Cellars and bunkers typically have exits pretty close together, whereas a culvert through a hill would have its ends out of sight of one another, and be much easier to leave if something you wanted to get away from was messing with one end. A tank or bunker with a single entrance/exit is the worst case here -- if that access is blocked while you're inside, whether by a natural disaster or a hostile creature, you're stuck and at the mercy of people outside to remove the threat.
I also think a lot about emergency egress and airflow management. Silos, tanks, cellars, and some basements are pretty terrifying from an airflow perspective -- passively, they can fill with any sort of heavier-than-air gas, and if you go in and pass out you'll fall to the bottom. (even if the air is perfect in there and you have a medical emergency, extrication is still an issue) Then whoever is trying to get you out will have to go down into it as well, and lift you straight up from it to get you out, perhaps waiting on a ropes rescue team, rather than just walking out. Even carrying a patient up a set of narrow basement stairs is worse than walking out along a trail, as a culvert-as-bunker could offer.
The flood risk profile of a level culvert through a hillside is also vastly preferable to a basement, bunker, or tank. If it's downhill out both ends, hardly any water can accumulate inside before it simply flows downhill and away. Tanks, bunkers, and some basements are often watertight enough and positioned appropriately to hold large amounts of water if it gets in at all.
So, a culvert through a hillside, with exits on both sides of the hill, seems like an ideal underground structure for concealment, access, and safety. Basically a cave, but better, due to the lower risk of collapse. Yet I hardly ever see people discussing them as an option. This means I'm probably missing some important disadvantage of the idea. Why do you think people so widely prefer cellars, bunkers, even buried shipping containers or school buses, over culverts? Are they too expensive? Too specific about what terrain they're great in? Too conspicuous to install? Something else?
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Edit to add resource highlights from thread:
back in the JFK dayz - he would spend time at the Kennedy Compound in Biscayne FL - no underground bunkering was possible - but something off site The Compound, accessible for helicopter pickup and able to take a nuke blast was needed >>> on a remote FL island, they built a surface bunker out of corrugated sheeting and then buried it under concrete & dirt - still there today .....
The President John F. Kennedy Bunker
Built in just a little over a week this preserved bunker was created to protect our most attractive POTUS while he was on vacation.www.atlasobscura.com
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Edit to add comments which a forum member offered anonymously, and said they're ok with me paraphrasing in the public thread. They said they have done a similar project and found more cons than pros. They have found it very expensive once all the peripheral costs are factored in. They mentioned that due to future plans for the site, most of the culvert is covered by soil, but part of the surface is protected only by foam insulation for the time being.
Pros:
- Their culvert handles cold temperatures well, staying at or above refrigerator temperatures when it's deep freeze temperatures outdoors
- They like how spacious it feels
- They're disappointed by the poor cooling performance during hot weather, finding that it heats above comfortable temps in heat waves, and is slow to cool off. The passive thermal performance is not satisfactory, and requires active systems to manage air movement and humidity to mitigate interior climate issues.
- Their culvert is not weather tight, and they say they had leakage problems with water coming upward into it from the ground
- They've had rodent troubles with their installation. The stress of playing mouse whack-a-mole is not to be underestimated.
