YJack Group is advocated to load only low pressure onto engineering pile body (to ensure the pressure on the pile less than own load).

In practice, many piles were designed as a high concrete mark, but their actual strength usually does not meet the designed value due to the complex positions of the jack group and low flow-ability of sediments. Therefore, the Safe Loading Principle is the essential of Bi-Directional testing to avoid pile damage caused by overloading.

In particular, some testing organizations fix steel plates on top and bottom of jacks and hope to enlarge the pile' force bearing area. But the steel plates (mostly 20~30mm)are usually not thick enough.

Ideal steel plate thickness should be calculated as per area ratio. See following drawing:

Loading Cell Group delivery pressure is 40MPa, the steel plate should be thicker than H＝0.212*d＝62mm if you want to lower the end bearing strength of the pile till 20MPa.