Thanks to everyone for the replies. I think that maybe I didn't make myself
clear: the vertical panel is standing on the concrete base, and I'm
intending to drill down through the panel and into the base. So in effect
I'll have a straight-through hole (in the panel) and a blind hole (in the
base). I'm hoping that because the base is up against the underside of the
panel, it will prevent any spalling in the latter (and thanks to Paul for
the correct term, which had eluded me).

I'm going to try it later this afternoon, so we'll see...

Bert