Cheapest, quickest way to make a cubic meter sized time buried capsule that will last 1000+ years

Modern formulations can include polymers that will make it much less subject to water penetration. But we’ve also recommended a waterproof exterior coating, and interior container. Concrete just makes it structurally sound.

To avoid it breaking up from mechanical action, and reduce that possibility from heating and cooling cycles the container should be spherical.

Just regular concrete cracks, so it’s not waterproof or even water resistant in the 1000 year time interval. It shrinks while it cures.

1/3 cement, 1/3 sand and 1/3 gravel

That’s why it has to be reinforced. If the exterior waterproof coating held up I don’t think metal reinforcement would be a problem, but it could be used to pre-stress the concrete giving it substantially more strength. But for a thousand years and worrying about it to survive even minor cracks fiberglass reinforcement should do the job. Small fibers in the mix will prevent a lot of cracking, and larger scale fabric will hold up to bigger events. There are even stronger cement formulations than used in typical concrete but with $1000 it’s tight to get this done.

Take a look at patents for nuclear waste containment casks, and then downsize a bit to fit your budget. If their designs are intended to last millennia, a slightly cheaper version should work for you.

Notice that a lot of these incorporate ideas expressed above.

This is what I was going to say. Note that the frost line in the mid-Atlantic states is never much more than 4 feet; burying it deeper than that should be sufficient to keep it safe from freeze-thaw cycles. (You’ll probably need a spot where the water table is deeper than that, though.)

Take the money and run. No one will know for 1000 years, if they are even able to find it.

Rethinking this - the OP’s constraints are pretty severe. One cubic metre is big, and $1000 is not a lot. In fact it is really really tight.

To recap a little. You need to keep water and oxygen away as a first cut, and also worry about anything you use degrading - especially if it degrades into something that may itself damage your capsule contents. And you need mechanical protection. Over 1000 years the land can’t be trusted to be stable. You should plan on having the entire thing submerged for extended periods.

HDPE is IMHO a good start. It is going to get you the basics of a long term shield, and it is cheap. But for a cubic metre, you are still talking real money wrt the budget. YOu can get sheet HDPE for say $100 a metre[sup]2[/sup]. But that eats a lot of the budget, and it isn’t clear how much DIY is allowed. Purchasing a ready made underground HDPE tank is probably a good start. Some are made with a manhole cover that would provide useful access, and could then be hot air welded.

Now you need to bury it, and to keep it safe. Concrete bunker seems to be the best bet. Dig a hole, line it with builder’s membrane, add formwork, and cast your bunker. This will pretty much deplete the $1000. Packing the individual items in the tank will help. The difficultly is that 1000 years allows a heck of a lot of time for otherwise very slow reactions to take their toll. Simple gas impermeable bags won’t really help all that much as they rate their gas holding capabilities is days, not millennia. Building smaller storage boxes and wrapping them in copper foil, then brazing them closed would probably work to hold down the worst. Proper brazing, not soldered. Might just squeak that into the budget.

The biggest problem will be protecting it from 1000 years of inquisitive humans.

No reinforced concrete for me. In a slightly elevated spot, dig your pit, put at least half a meter of rock ballast (meant to allow some drainage since you want it buried.) Put your relics in thick clay jars, the type Asians and Africans use to store drinking water. Your cubic burial vault must be lined on all six sides by at least 8 inches of bentonite or ordinary potter’s clay. “Drown” your entire vault with more ballast. Then either bury the whole thing 2 meters deep or shallower but with a raised mound.

How about a little cheating on the OP’s specs. If you can’t find a natural cave, excavate a .75m x 1.2 meter tunnel 1.83m deep. Choose moderate hardness sandstone or volcanic tuff. With a pneumatic pick, you can excavate it in a day. Put your jars in, fill with sand or gravel, cement it in.

Nah, I’m thinking this is a school science experiment from 1000 years in the future. They have time machines, but chickens have gone extinct, so they can’t drop eggs off the school any more. They have to come back 1000 years with a limited amount of cash and bury a time capsule. Go home, dig them up and get graded on how intact the contents are.

Nice attempt at getting us to help you with your homework, future boy.