Which Theory is Also Called Stress Difference Theory?

Maximum normal/Principal stress theory/Rankine's theory is also called Stress Difference Theory. This theory assumes that failure occurs when the maximum principal stress at any point reaches a value equal to the tensile stress at the failure of a simple tensile specimen. This theory does not consider the effects of two other principal stresses.

The vertical distance of the total effective earth pressure from the top of the wall = y̅. For a triangular pressure distribution, we know that y̅ = (H/3) at the base of the wall. The failure surface plane forms an angle α = 45 + (ɸ/2) with the significant principal plane.