If I understand Correctly the I wall is a retaining wall and it is not like an inverted T and L above the top, the procedure of designing The I wall if any loads above is to determine the moment at the top of the stem, then continuing the analisis not transfaring moments from the base to the top wing, the stability of thiswall remains the same
Sum (H) =< Sum (V)*tg(2/3 Fi) (sliding stability)
Sum (Mo) =< Sum (V)*x (overturn stability)
wheres Sum (H) is the sum of horizntal Soil load
Sum V is the sum of all the vertical loads
x is arm between O (the point of turning) and fixing load
Mo is the sum of the adverse loads
Note that some vertical Loads in this case might be Adverse
Note that the soil under the top stem will not bare the soil weight above
I hope I could help, Try to mail me a drawing to understand the problem more sido_r@ureach.com