I live in a 1950's single family brick cape cod home (30' x 30') just outside Philadelphia. We have always dealt with a wet basement and in particular mud/clay and silt coming in at the basement floor to wall joints. The basement height and height to ground are both 7 feet. The basement walls are rubble stone ~16 inches thick. The stones appear to be ~ 1 ft long at the "footer" level. The inside of the wall is parged 1" thick and the floor is monolithic ~2" thick. An interior french drain was installed before we bought the home over 10 years ago. After about 5 years, a decent amount of mud started coming in because the french drain system clogged along one wall... Anyway, being an engineer, I am concerned about foundation undermining and thought I would mass underpin the rubble foundation so I could place the waterproofing a minimum of 6" above the new footer instead of below it which it currently is. This involves underpinning in sections of 4' between 14" to 18" below the existing foundation and leaving a 2" - 3" gap above the pour to place dry pack the next day. I have a drawing that calls 2 #5 bars fairly continuous between the 4' sections.
My questions are:
1) In a 70 year old home, what should be done while excavating to ensure the "footer" stones don't drop? I don't think that ones above them will due to the interior parging, but not too sure about the condition of the mortar inside the wall.
2) Since I'm only doing this for waterproofing and the floor is staying in the same place, do I need the horizontal rebar? The floor will laterally support the bottom of the original wall and there will be 6" or soil at the bottom of the new sections.