Earthquake Induced Pile Failure

So far, among the known foundation technology, Pile foundation is the safest deep foundation. But it is noticed that piles are failed during past strong earthquakes. This failure of pile is structural and almost all of these piles pass through soils that are susceptible to liquefaction. During earthquake the soils become liquefiable and the piles lose lateral confinement through its length and plastic hinges are formed that leads to structural failure. 

Bending moments or shear forces induced on the piles during earthquake exceed that predicted from Codes of practice. All current design codes apparently provide a high margin of safety (using partial safety factors on  load, material stress which increases the overall safety factor), yet occurrences of pile failure due to liquefaction are abundant.

This implies that the actual moments or shear forces experienced by the pile are many times those predicted. It may be concluded that design methods may not be consistent with the physical mechanisms  that govern the failure. In other words, something is missing. This research investigates what is missing from the current understanding of earthquake-induced pile failure by analyzing the postulated hypothesis of the existing design codes of practice, such as the Japanese Road Association Code (JRA 1996), NEHRP (2000), and Eurocode 8 (Part 5).

To avoid plastic yielding it is experienced that overall safety factor of a typical concrete pile considering the bending mechanism may range between 4 and 8. This is due to the multiplication of partial safety factors on load (1.5), material (1.5 for concrete), fully plastic strength factor (ZP/ZE = 1.67 for circular section) and practical factors such as minimum reinforcements or minimum number of bars. Therefore, one should not expect failures unless wrong failure mechanisms are postulated.