the elevator in question is in the large chamber between the train you use to crash through the tunnel barrier and the control switch that changes over the tracks. in the center of this large chamber is a big hole with a waist high concrete barrier around it, this is where the elevator is. after you change the tracks over reinforcements will begin to arrive. run back to the center chamber from the control room and take cover. the elevator will be descending from the ceiling of this chamber. there is a golden wench/mechanism on top of the elevator, shoot it and once the elevator crashes down the hole the achievement should pop.