How to design and build a fortified compound in a 12-hour daylight period?

Question

Situation Overview: A group of 16 (actually 100, but the others aren't relevant here) people have suddenly found themselves transported to a different world. It’s a hybrid setting, with tech and magic. The magic system is fairly standard(ish), but it's limited only to the teenagers in these displaced people, for plot reasons.

In the group of 16, there are only three teens with magic (one without, but again, plot). These three have access to Ice, Fire, and Earth magic, but can't actually use them very well yet. The earth mage (the obvious choice) can make walls to an extent, but can't build something with a roof that doesn't collapse, yet.

The 13 remaining people all have some access to equipment from our world through a system store, but can't currently afford any earth-movers or other heavy machinery. Access is limited to items the characters are intimately familiar with and priced according to familiarity and complexity. In other words, the resources available are pretty much only what they have on hand for the moment plus or minus a few small items.

Current tools and resources available: 16 people of various ages (see below for more info), one hand axe (hatchet), one entrenching tool, one sniper rifle (.50 cal), one pistol (.40 cal), five assault rifles (5.56mm), one first aid kit, one battlefield trauma kit (? not sure what the name is, or if it has one), many dead owlbat carcasses, also forests nearby. Access to water and food is covered through the system store.

Human resources: Two British material chemists, one fresh college grad with a biology degree, one surgeon, one civil engineer (road construction focused), one US Customs agent, two USAF pilots (rotor and fixed wing), one USAF pararescue jumper, one retired SEAL (medical-lost leg), one US Army armor officer, one USN Captain (destroyer skipper), the magical teens mentioned above, and the last teen who is more or less an insurgent/child soldier (she grew up in a warzone, scout/sniper specialty)

The location: The build site is on a rocky outcropping that's about 455 acres. It's bordered east and west with tropical forest (jungle), south has a smallish 20ft cliff (sheer drop) down to the ocean, and north has a small, brush covered mountain (around 1500-2000ft). Mountain hasn't been explored yet, nor has the jungle past a few hundred feet. The current camp is located on the northern edge, close to the mountain (about 20 feet from the base of the slope) and about equidistant from the jungles.

The problems/limitations: Only 12 hours of daylight, plus or minus. The daylight hours are somewhat calm, dangerous creatures can be encountered in the jungles but most avoid the rocky outcrop except to transit to the other side. At night a predatory species of owlbat (bat-like body and wings, owl beak and claws, sensitivity to sound and bright light, size can vary from house cat sized to medium dog sized) comes out in large numbers. They are less than friendly and can fly, obviously, so walls are of limited use. There is also a species of rock lizard that spits a viscous goo that acts like a high-explosive variant of natural napalm when set alight (the lizard can't light it, though). Moving camp isn't a viable option, the jungles are far more dangerous as the pistol and assault rifle are woefully ineffective on the larger wildlife (boars the size of a VW Bug).

How to build a credible (read: believable) simple fort in 12 hours?

Best answer would be one that can give a credible design for construction of a defensible campsite/compound while considering the limited resources, time, and location available. Must be able to defend (or at least protect) from aerial and ground predators. Ideally, it would be expandable over time.

Answer 1

The owlbats seem like the only real threat here (everything else is defeated by a circular wall raised by the earth mage and some sharpened sticks at the worst). However, predators do not generally take fights against significant resistance, so we don't need to actually be able to kill whatever comes at us: just be scary enough and capable of throwing out enough damage to get them to go hunt something else. I'm also assuming minimal use of the system store, so I'm going for using that to get tools and building your own defences: feel free to substitute pretty well everything gathered/made here with purchased alternatives, if you like.

My suggestion would be, if you don't want to go for "just bury yourselves":

1. Get the earth mage to raise said circular wall, with an equally-deep ditch around the outside. It's (presumably) easy, it uses at most 1/13th of your human resources, and it will deal with most threats. Make it as small as it can be while leaving room for all 13 of you, with a couple of people awake on hard at any given point and everybody else sleeping: if you've got extra time, build extra less-well-defended areas (presumably, you don't actually need to defend anything much other than yourselves defended fully: it's not like the predators are interested in whatever you're storing out there). If the earth mage can manage a bit of an overhang on the inside, that's a bonus (if nothing else, it'll give you somewhere out of any potential rain). Leave a gap for the entrance and have the earth mage raise that bit last, once everybody is inside, then lower it again when you want to leave in the morning.
2. Get some people making sharpened stakes from the nearest trees, and embed them in the ditch. If your earth mage has the control/time to lock them in place with her powers, so much the better, but if not, mundane approaches will work (that civil engineer will have some good ideas, probably).
3. Stack all of the surplus flammable materials acquired from the above, plus as much other flammable material as you can find in a nice big circle around the outside of the barrier. Animals are not generally fans of running or flying into fire or smoke, so if things get bad, the backup option will be to set all of it on fire and let the smoke and flames (and, if any of those lizards spit on the wood, the bonus explosions from that) scare away basically everything. How they use this depends on how hard/dangerous it is to gather that wood/etc.: if it's easy, just make the pile massive, light it at whatever time the predators come out, and go to bed. If it's hard, it's an emergency measure for when everything else fails.
4. Make a bunch of longer stakes (long enough to stick out a couple of feet above the tops of the walls), and arrange them vertically around the inside of the compound. Again, the civil engineer can make something suitable. Run horizontal poles across the top in a grid narrow enough to stop an owlbat getting through. If you've got enough time, put the poles edge-to-edge to make a rough roof, but that's more for shelter from the elements than part of the defences.

And that's it. No predator is going to hurl itself at a wall of spikes, no matter what's on the other side. Honestly, this is already hopeless overkill for dealing with predators: you could probably get away with just building a big fire to sleep near, if you're only worried about non-intelligent predators.

Answer 2

Pillars of flame

Step one: collect flammable material from the edge of the jungle/brush from the mountain. Preference should be given to things that cause a LOT of smoke and burn slowly (Can be avoided if the pyromancer is the "can make flames appear and burn without fuel" type) This should essentially be what everyone not the pyromancer/earthbender is involved in for the entirety of the 12 hour period. The pyromancer should be resting, they have a busy night ahead

Step two: While the fuel is being gathered, Earthbender should create a 15ft circular wall around a space capable of fitting your entire party and the fuel they've gathered comfortably. The wall doesn't need to be particularly thick, it's there to mask your party from view of whatever megafauna might be around. Ideally they just raise up a circle of 3 inch thick stone or something.

Step three: Earthbender creates a ditch in front of the wall, 10+ft deep, wide enough that nothing can jump from the far side to the wall itself. The depth should really be as deep as the earthbender can manage, so when the rest is set up they should spend the rest of their time deepening/widening the ditch.

Step four: Raise up pillars of stone/earth 12ft tall, with a slight depression at the top (think a shaft with a bowl dug into it). they need to have a cross section of a couple feet. Top them off with piles of wood/other fuel. You want these every yard or so.

Step 5: At dusk/when owlbears appear, light the fires on top of the pillars. The pyromancer's job is to keep those things burning all night. Depending on your cast of characters and the power of your earthbender, you might have shifts which climb makeshift ladders to pile more fuel on, the earthbender might lower low-burning pillars to add fuel, or raise up temporary "steps" so they can be refilled.

What does this get you? The wall/ditch should obscure you from view, and be enough of a weirdness to keep the larger predators away. The smoke will mask your party's scent. The combination of fire and smoke should also keep the owlbears from wanting anything to do with you. If your party does things particularly well, the walls being several feet higher than the fire-pillars will also stop the flames from being seen from a distance, which also helps keep away the curious come nighttime. When dawn breaks the earthbender lowers a patch of wall, fills in the ditch, and off you go!

Sidenote: If your walls need to be of any serious thickness (several feet) then you'd also want some spiky vines, a "step" with more fires on the inward side, or worst-case fires around the top to prevent the owlbears from landing on the wall and then slipping down the inside in the night. Mind you this whole thing is overkill on my part, you could easily get by with a ditch, three fires around the perimeter, and a few sharp sticks. But as they say there ain't no kill like overkill!

Answer 3

Your civil engineer will have a strong background in Earthworks and will be able to advise your geomancer in how to build a sound structure even without being able to build traditional ceiling. First displace a torus of Earth like a large foxhole, then raise up a bunch of stone pillars that can rest against the torus of earthwork and come together as a cone. Since they are not flat horizontal, they are not under nearly as much sheer as a flat "ceiling". This puts any stones your raise into a state of compression instead of tension which pretty much all rocks do way better in (and why you can make a wall but not roof). When you are done you will basically have a cairn or barrow like structure. If there are any gaps too big, just keep stacking stones until the animals can't get in.

When you have it down to one way in and one way out, have everyone climb in and seal the hole off for the night. There will be enough gaps in the stone to breath, but nothing any predatory animals can get in through.

Answer 4

Why could you not create a house? Yes, you can!

Building a makeshift house is part of survival basic knowledge your SEAL should have; This, along with a civil engineer (even when not specialized in house building), a mage who can create trenches, walls and/or even out a platform to build on, they shouldn't have issues building something which is reliable enough. For the roof, using overlapping sticks along with big fern leaves -or equivalent- on top should do the job. Most if not all survival manuals should be able to detail more accurately how to do this than me, if you're interested.

Also, note that if the people stay quiet and undercover, lighting no fire, there is no reason for the owlbats to tear the shelter apart to hunt them, there should be targets which are far easier to get a claw on and which you can be a lot more certain they are there. If they are attacked, then it's likely they are on their territory, which isn't a clever placce to build on, especially when you've already met them.

Getting the most out of what you have

Here are some ideas to improve chances to survive in the wild, using the most of your team and resources :

• Plan out which spot is the best with the civil engineer, the insurgent, SEAL and biologist. Insurgent and SEAL for a tactical point of view, civil engineer for possibilities to build, and biologist to avoid animal paths and nests. The captain may be able to provide a pair of small binoculars to quickly restrict the choice without moving around too much.
• Pilots may provide a set of talkie-walkies/radios to help planning out things, especially if there is a problem.
• If you have enough resources in the system store, you can buy a parachute and use it as a ultra-quick makeshift roof, using some stone weights to maintain it. Alternatively you can get an inflatable boat and an air pump, too. It doesn't take "much" space when closed and has not very complex patterns, so it shouldn't be that expensive.
• A chemist could get some hyper-strong glue to help. It's small, not overly complex yet very useful to create more stable buildings. Another item with the same purpose is duct-tape rolls.
• To avoid becoming thirsty (12 hours + a night is long), throw ice magic into any recipient, then melt the ice up. You don't need to look for a river or a pond that way.
• With ice magic again, dig, freeze then melt moats around your shelter, so that no lizard can enter (assuming they cannot swim).
• If the soil is made of clay or is simply wet, cook it up to harden and reinforce it to make it useable for structures.
• Don't ever use firearms during the night, they will most probably attract predators which are not affraid of rifles (aka the worst ones). There is one exception though, it is when the rifle is used far away from the survivors to get the attention elsewhere.

And some ideas in case they finished building their main defenses before the night comes :

• Put owlbat lures around and away of the main house : Plant a woodstick from a oily tree (a biologist and/or chemistry should recognize it or make a compound from the store) and burn it with fire magic before night.
• Gather up the dead owlbats and use a trap of any kind to ambush the predators that may prey on such animals. Traps can be a big rock falling over the bait, fire/freeze from a distance (bonus if you managed to get some lizard's spit), or booby-trapped rifle, among many others.
• Depending on how the store works, a biologist could get a pheromon bottle and spray it to attract or repel some animals. Check if any animals of use can smell, then use their gland as a basic component to replicate it.
• If you happen to have some store money left, some flares and flare gun can be useful in a pinch to direct attention away AND get a view of the targets.