Mining operations and quarrying spring to mind! The reduction in wood use should probs to be advantageous long term in reducing deforestation in later imperial period (only way to deep mine or quarry was to use wood setting/fire up until invention/perfection of gunpowder) by itself!!!!
Canals of all types, one mega project other than Corinth canal would be the connection by water of the Danube and the Rhine river systems.
Siege operations will naturally flow from the perfection of gunpowder mining methods so sapping is in big styleee!