The only technical reference I have for augercast piles is Transportation Research Record No. 1447, published by the Transportation Research Board of the National Research Council (National Academy Press, Washington, D.C. 1994). It is a compilation of articles on the subject.
Augercast piles derive most if not all of their resistance through skin friction, not end bearing. They don't need to be designed as columns. Quoting from the Record No. 1447 article "Managing the Installation of Augered Cast-In-Place Piles" regarding reinforcing steel:
"ACIP piles can be reinforced to resist lateral forces and to increase axial compression or tension capacity. The most common reinforcement is a single steel bar introduced into the pile immediately after casting and penetrates to the bottom of the pile. Centralizers are required to be certain that the bar remains within the pile section. Less common is introducing the bar through the hollow stem as grouting begins. A bar that is at or neqar the center of the pile has only a modest effect on the bending resistance but can provide significant tension capacity if adequate bond strength is available.
Bending strength can be provided readily by introducing a reinforcing cage or a steel member like a lightweight H section or a pipe into the pile just after grouting has been completed and before the grout has set. These sections also require centralizers to ensure they remain within the grout section as they are pushed into place. In general, there has been limited success pushing steel sections or cages to depths greater than 20 ft (6 m). Ordinarily this depth is sufficient to reinforce the pile against horizontal forces applied at the ground surface, but a shoirter depth limits the usefulness of the ACIP pile for use in cantilevered retaining structures that are more than 10 ft (3 m)to 15 ft (4.5 m) high."
I've used 12" augercast piles here in Florida, using a single #8 bar as the central reinforcment. The centralizer referenced in the article is commonly known as a "football". I would consult your geotechnical engineer regarding lateral bending, in order to determine the size of your cage or steel member (I use cages). Based on your required lateral capacity, he can run LPILE for you to determine bending moments and the required depth of reinforcement.
I agree with the others that 12" is too small for 100 tons. My guess is more like 18" to 20" diameter.
