Underpinning an existing slab on grade during renovation

[woodman1967]

Hi all,

We are adding an addition to an existing garage. The design is looking to add hallway perpendicular to an existing industrial garage. The hallway will be founded on a four foot frost wall. The existing garage is on a slab on grade with a 12" thickened footing. What is the best method to avoid undermining the existing slab while excavating for the new foundation?

Thanks for your help,

 

[tadeng]

Excavate the soil next to the existing building so that you get a maximum of 1:1 slope away from the bottom of the existing footing.