existing foundation wall abutting a new found. wall

huangyhg

existing foundation wall abutting a new found. wall
we are putting an addition on an existing building with no basement. the addition will have a basement. how do we reinforce below the existing footer (aprox 3 ft below grade) and not diturb earth below; so we can dig for the new footer (approx. 12 ft below grade). the new block wall will need to be flush against existing block wall above grade. i need a detail.
thanks in advance!
d. hutchison
underpinning is in your future
other option
pull basement away from existing footing to get out of the influence zone.  construct a 4' to 6' wide section of slab on grade then start the basement.
underpinning methods may vary depending upon the soil conditions that you are dealing with. as sperlingpe said, moving the basement away will potential save significant  money.