If you are concerned about drilling into granite, don't be. A good carbide tipped masonry drill bit will walk through it, provided you have the right hammer drill. Hilti was one of the first, if not the first, to have the percussion and speed actions correct. I had a Hilti saleman come out to the jobsite where I was fastening a multitude of oak boards to a concrete wall. I had been using a Milwaukee hammer drill, and going through drill bits like there was no tomorrow. We were only drilling 1/4" holes, but the concrete was very hard. He handed me the Hilti drill with their bit in it, and the first hole I drilled it felt like I was drilling soft wood. That was over twenty years ago. Since then, Bosch, Metabo, DeWalt, Porter Cable, etc. have made drills with the same drilling action and speed. I guess Hilti's patent ran out?
Anyway, getting back to your task, I would say, looking at the photograph of your viaduct, that unless you take it slow, you could run the risk of knocking some of those stones loose. Don't force the drill. Let it get a bite first. Then you can apply slight pressure to finish the hole.
I remembered another method we used once in awhile when we didn't have any masonry anchors. We would drill a 3/16" diameter hole through the wood to be anchored, and keep drilling down into the concrete. Then take a piece of tie wire, bend it in half and stick it into the hole in the wood and down into the hole in the concrete. Next we would take a 16 penny nail and drive it through the wood and down into the concrete. There was no way that was comming loose. And it saved the boss alot of money on anchors.