dig trench to install internal french drain is ok on a no footing basement?
We are thinking about put internal french drain down to our full basement. The house was built in 1950's, a one floor ranch house, in Boston MA. The basement is poured concrete about 7' below the ground. There is no footing. There are no cracks on the walls.
We have done outside grading and french drain. But in very heavy rain, there are still water come from the wall-floor joints due to the watertable is higher than usual then. That's why we are thinking about internal french drain system.
Because there is no footing, I am worrying about cut concrete floor and dig a trench near the concrete walls for "pipes" will weaken the foundation. although the trench will be filled with gravels.
do you have any ideas and suggestions about this situation?