The right sign for "tunnel" depends on whether you mean the noun or the verb. It also depends on what the tunnel looks like.
TUNNEL (verb)
If you mean the verb:
* You can use a cupped hand doing a scooping movement to show a backhoe or similar bucket-type device.
* You can use two cupped hands doing scooping/digging movements to show an animal "tunneling"
* Use an index finger doing a forward corkscrew movement to show a drill-type device tunneling,
* Use an index finger bending and unbending (1,X,1,X) as it moves forward to show the tunneling of a worm (or similar creatures).
TUNNEL (noun)
See: CAVE
See: PIPELINE
See: POLE
