When a new mine is constructed, two shafts are excavated down
to the salt deposit, usually between 500 feet to more than 2,000
feet deep. Shafts are about 20 ft in diameter and lined with
concrete. After the shaft is sunk to the salt, rooms are mined in a
planned pattern by undercutting, drilling and blasting. An
undercutter cuts a horizontal slot or kerf along the floor of the
advancing room to provide a second free face for blasting. A
drilling rig drills a series of holes into the face, and an ammonium
nitrate-fuel oil mixture (ANFO) is pneumatically placed into the
holes.