Japanese Code for Understanding and Designing of Pile Failure Due to Liquefaction

Piles are one of the most common and safe deep foundation that are practiced yet for foundation solution where bearing capacity of soil at shallow depth is poor to support a heavy or sensitive structure. But in recent years, though foundation engineering has been developed greatly, it was not determined that why piles are failing during cyclic loading that is generated by earthquake. The recent understandings about failure of pile are as follows: 

When soil gets liquefied, it loses shear strength. This liquid soil has no resistance to flow resulting soil to dragging and flow with it any non-liquefied  crust over it. Piles are dragged with the crust and deflection of pile results bending moment. When bending moment exceeds the capacity of pile it get failed. This phenomenon is sometimes called failure due to lateral spreading.

It can be concluded that the recent observation on the failure mechanism shows that piles are pushed by soil during earthquake as a consequence of liquefaction. This mechanism is sometimes proved where deformation on ground surface around pile foundation is observed.

The Japanese highway code of practice (JRA 1996) advises design engineers to consider following assumptions to provide sufficient bending strength against lateral spreading: 

1. Non-liquefied crust offers passive earth pressure to the pile

2. The liquefied soil itself offers a drag equal to 30% of total overburden pressure. 

Other codes such as NEHRP 2000 and Eurocode 8, part 5 (1998) also focus on the bending strength of the pile.