Rules for Cave-ins, Avalanches, or otherwise being Buried Alive?

[Nefreet]

I tried a Ctrl+F search in the Core Rulebook and likewise couldn't find anything on archivesofnethys or here.

Are there rules anywhere for being buried alive?

Suffocation isn't as much of an issue with modern armor, but in Pathfinder the rules still cover crushing damage and ways to escape.

Anyone know of anything I've missed?

My specific encounter:

The PCs are shooting from the protection of a train at two gargantuan creatures that are described as being "upward of 30 tons" each. One character exits the other side of the train. I want to have one of the creatures climb over the 10-foot tall train (still a chance of failure due to its poor Athletics) and engage that character.

I'm imagining that the train won't be able to support the creature doing that, and will collapse under its weight.

The PCs inside won't technically be "buried alive", but will probably have to use some variation of the Acrobatics skill to Escape. But Acrobatics DCs don't really represent this sort of challenge.

Absent any defined rules, how would you run this encounter?

[The Ragi]

Something kinda like that happens in one of the Adventure Paths.

Here's how they handled that particular encounter:

Spoiler:

Dead Suns book 4, page 28:

Getting Buried: Characters who are buried in rubble take
10d10 bludgeoning damage (Reflex DC 18 half). A buried PC
takes 3d6 bludgeoning damage per minute as he is slowly
crushed and suffocates (Fortitude DC 18 half). A buried PC can
free himself with a successful DC 25 Strength check, and can
attempt one once per minute.

A character who isn’t buried can dig out someone who is.
Using only her hands, a character can clear an amount of bulk
of rocks and debris equal to five times her Strength score in 1
minute. A 5-foot-square area contains 200 bulk of loose stone.
Armed with an appropriate analog tool, such as a pick, crowbar,
or shovel, a digger can clear loose stone twice as quickly as
she could by hand. At your discretion, other technological
tools might be able to clear loose stone even faster.

[Nefreet]

Thank you for that!