In the movie, Chuck Norris's character, Colonel Nick "Rambo" Alexander, gets buried in a truck when a bridge collapses. He then uses the truck's engine to power a hydraulic jack system he builds, pushing the truck (and himself) out of the ground.
It's a classic, over-the-top action sequence that plays on Chuck Norris's tough-guy persona and is a good example of the kind of absurd action that made the movie a cult classic.