In the last post we have discussed about assumption about piles as free standing columns. There we have learned that even in soft clay, the soils provide sufficient lateral confinements to the pile not to be treated as free standing column. There we provide some conditions to be treated pile as freestanding one; of these, one is when soil gets liquefied by earthquake. We will discuss about this phenomenon is this post.
Recent exploration about mysterious failure of piles during earthquake is liquefaction. Even under axial load without other components plastic hinge can be produce in slender pile with liquefaction in surrounding soil as there have no buckling stability.
During construction and driving of pile, it is inherent to remain imperfection, lateral loads generated from lateral spreading in surrounding soil with/or inertia, stimulate the increment of deflection. This stimulating defection accelerates collapse of pile.
The pile that located in liquefiable soil having proximity to be suffered by earthquake vibration should be designed for Euler’s Buckling. The P-Δ effect of is also considered to render safety to piles during earthquake. As a slender pile are subjected to more buckling than a non-slender pile, there have a tendency in modern construction to use few greater diameter piles instead of providing multiple piles of small diameter in liquefiable soil.
Due to lack of knowledge in such behavior of pile during earthquake in liquefiable soil many structures were supported on not-buckling resistant piles and still some practices are performing in many parts of world which are all to be retrofitted to reduce or eliminate buckling instability. We have provided more explanation of such failure of pile in accordance with Japanese Code.