mouvement alternatif vertical

CONT: [...] le forage par battage [...] consistait à attaquer la roche au moyen d'un trépan [...] animé d'un mouvement alternatif vertical qui assurait le creusement du trou.

CONT: Early wells were drilled with impact-type tools, in a method called cable-tool drilling, in which a chisel-like bit was suspended from a cable to a lever at the surface, and an up-and-down motion of the lever caused the bit to pound the bottom of the hole and chip away the rock.