Your grandfather basically dealt with explosives, planting them, finding the enemy's, and as the other posts said, digging tunnels sometimes and planting explosives under enemy trenches. If your grandfather is still alive, take a notebook, go see him; have him talk of ALL his memories and write it ALL down. It will be a treasure greater than any of the gold in Fort Knox.
He was an engineer and was responsible for trucks on the battlefield, and for lifting and finding landmines
He was in the engineer corp. In the first world war sappers prepared huge tunnels under enemy lines and filled them with explosives.