Bedrock is the most stable of foundation bearing site materials, but whether it is shale, granite ledge or any other type of solid rock, it must be cut away as specified by the engineer. Yes, stone can be demolished using explosives, but in an urban environment is not always feasible because of the proximity to neighbors and concerns that their use could damage nearby foundations. There are a couple of other options available to us, depending on the type of stone and the volume of work that needs to be done.
We frequently use an expansive demolition grout. The process is similar to using explosives, in that the stone is prepared by boring holes. Instead of filling the bores with explosives, a slurry of grout is poured in, which expands as it sets up and breaks up the rock, just as explosive would, but silently and safely. The rock can then be broken up efficiently with a machine mounted hydraulic hammer.
Depending on the geology, it may be possible to break up the stone using just heavy hydraulic hammers. Once the stone is cut away, a spread footing is dowelled into the ledge in order to support the foundation. A series of holes are drilled into the ledge and rebar is epoxied into the holes and a concrete footing is poured around them.