There seems to be some type of irony here in that the design may have created cracks just above the drains just so the drains can remove the water from the cracks....
When I saw detail “A” in post 2132 I said to myself I would shoot one of my civil staff for detailing something like that. It goes right back to that faulty slab on solid rock issue I have whined about in previous posts.
Detail “A” facilitates a weakening of that slab right along that drain pipe by thinning the slab. If the slab had sub-base rock below it, the sub-drain should be put in a french drain channel below the layer of sub-base rock. Having it run slightly diagonal down hill is a sensible feature that they made in the field but having no uniform sub-base with this drain below the sub-base is substandard in my thinking even for the 60s.