Expert: Robert Cummings, P.E. - 3/24/2008

Question
Mr. Cummings thank you  for the additional information on the Slope Creep issue. You have helped me understand the underlying causes and fixes of dealing with foundations sinking in wet clay. I took a 2 foot soil auger and drilled down below the existing footer and found a "very moist squishy" clay like material directly under the footer 85%clay 15% sand(12 inches below ground level). No wonder the wall is settling! It held its shape when squeezed by hand and could squish between fingers due to moisture. At approximately 30 inches the sample was still moist to the touch but more sandy(75%) vs clay 25% and would hardly hold its shape when squeezed by hand and not squish through fingers.
So I can realize that I will have to dig down very deep (in excess of 3 feet) to find "solid" ground.
As you stated that added supplemental footing could add to the weight of the "structure" I am now realizing that I cannot and should not add complete footer the length of the wall (and 5 feet around each corner), as it would have to be so deep that it would easily require 20 yards of concrete and could fail anyway due to added weight.
What I am led to consider now is excavating, say, five 2 ft wide and 4 ft deep holes(drilled shafts) below the existing footer(along the 48 ft length) and fill them with concrete up to the existing footer. I would consider placing a 2 ft adjustable floor jack at the interface between the existing footer and the concrete filled shaft but am not sure if that would be wise, since it could crack the existing footer if the pressure is too great at such a small load point. But from my understanding helical piers tie into existing footer in a similar fashion and are spaced about 10 feet apart.
I am going to rent/purchase an auger that will drill down at least 6 feet, so I can determine where this so called stable soil/bedrock is. If I cant find it then the helical piers may be the best solution.

Answer
I think you are on the right track.  I hope 4 ft will be enough but even that would be an improvement.  

Be sure when you place rebar cages in the underpin pier excavations that you maintain clearance of at least 1 inch, preferably 2, all around to ensure that soil does not come in contact with the rebar.  This is to prevent rebar corrosion.