The criterion has its origin in a mistaken quotation of a now 70 year old statement by Terzaghi (1942). Terzaghi wrote: "the failure load is not reached unless the penetration of the pile is at least equal to 10% of the diameter at the tip (toe) of the pile." (For full quotation ...
vi. The site operatives often lack skills in construction of bored piles with casing or bentonite support fluids giving rise to quality problems of the pile executed. vii. For both types of aforementioned bored pile technics, the inadequacy of the method or equipment used is a technical hazard ...