It seems that the game can only handly actors of up to 20,000 kg, after which simply standing upright will cause impulse damage, no matter how high I set the impulse damage threshold. Shame, I had wanted to make a drop pod that is heavy enough to crash through concrete without exploding, or a steam roller that can flatten the ground.

For the drop pod, instead of making it really heavy, you can just give it an emitter which digs the ground instead of crushing it. same for the steamroller, just make the emitter spread alot.

Emitters are only a compromise becasue they would keep on digging until the actor falls through the map. My bunker busting bombs and armor piercing cannon also don't work because the explosive gibs due to impulse before they get to use their time fuse.

Well, currently CC doesn't simulate pressure, so it's either you go all the way to the bottom, or you don't. You can't really "compact" the dirt terrain.

But for the droppod one, you might want to try using sharpness.

Just as I thought, since crushing the ground will slow the actor down, there is a limitation to the actor's penetration based speed and mass.
By increasing ImpulseDamageThreshold as well as GibImpulseLimit I finally managed to create a unit that can survive crashing through concrete/metal. So I made a rocket that can punch through different thickness of ground depending on how much weight you add to it, I also made a deadweight item that you can give the rocket to change its mass.

Huh. Actually, thats kind of a neat idea. The other implementation of this kind of thing I saw just had it so you'd choose different rockets with different penetration levels of their own. Your idea consolidates things a bit more nicely.

got a screenshot of rocket that punched through bunker roof to deploy troops, although the deployment process is somewhat accident prone.