Tunneling
Some species are able to tunnel through dirt and sand at ½ movement speed. Digging requires a full action to start the hole, once dug if your race is able to burrow. Burrowing through sand does not require an initial hole.
Cave-ins
Cave ins can happen in two ways
Someone on the surface stands above the tunnel and succeeds an SR 15 vigor roll, +5 per 5 feet deep the tunnel is.
The character digging critically fails their roll to dig.
The digger must succeed an SR 15 Fortune roll or the cave begins to spread at a rate of 5 feet per turn in every direction.
Each turn the digger makes an additional SR 15 Fortune roll to see if the cave-in continues to spread.
The SR decreases by 2 for every 5ft away from the initial cave-in
If a character is caught in a cave-in, they begin suffocating. After 1 rotation they can begin digging at ½ speed if they succeed an SR 15 Vigor roll.