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The seismic waves generated due to earthquake cause the ground to vibrate and create severe natural disasters. Various types of ground deformations occur during vibration and such deformations leading to failure can be recognized as ground failures. The dramatic response of saturated loose sand deposit due to earthquake can be hazardous to constructed facilities in the seismic regions where such soil deposits exist. In liquefiable soils, earthquake excitation shall induce the development of excess pore pressure and when the excess pore pressure reaches the initial overburden effective stress, the soil is liquefied.
Liquefaction behaviour was observed during a number of earthquakes in the past. During Alaskan Earthquake (1964), liquefaction was the main cause of severe damage to 92 highway bridges, moderate to light damage to another 49 highway bridges, and moderate to severe damage to 75 railroad bridges. During Niigata Earthquake-Hamada (1964) liquefaction induced damage to the foundation piles of Yachiyo and Showa bridges and Niigata Family Court House building (NFCH) building and underground pipelines. During that same earthquake, girders of Showa Bridge toppled as the support structure and piles moved excessively due to liquefaction. During Kobe Earthquake (1995), liquefaction was the primary cause of damage to many pile supported or caisson supported bridges and structures. For example, Shin– Shukugawa Bridge was subjected to excessive pile foundation movement due to liquefaction. It has caused the collapse of the Daikai subway station. In the 1995 Kobe earthquake, massive liquefaction of reclaimed fills caused serious damage to numerous pile foundations of buildings, storage tanks and bridge piers.
The unprecedented level of damage to foundations of modern engineering structures stimulated a great number of research studies in an effort to improve the understanding of soil–pile interaction in liquefied soils and seismic performance of pile foundations. The effects of liquefaction on deep foundations are very damaging and costly. Lateral spreading especially occurs close to free boundaries such as rivers, the shore or quay walls, as here the water table is high and the boundary conditions favourable.
This implies that the bending moments or shear forces that are experienced by the piles exceed that predicted by those design method (or code of practice). All current design codes apparently provide a high margin of safety (partial safety factors on load, material stress), which would mean that the actual moment or shear force experienced by the pile is many times the predicted moment or shear. It may be concluded that design methods are not consistent with the physical mechanism that governs the failure. It is essentially a kinematic soil–structure interaction process involving large ground and permanent foundation deformations, with the deep foundation and superstructure responding pseudostatically to the lateral permanent displacement of the ground. Predicting the behaviour of a pile foundation in liquefying ground during an earthquake requires consideration of design motions, free-field site response, superstructure response, and soil-pile-superstructure interaction.
The foundation may be exposed to large lateral soil pressures, especially passive pressures from the nonliquefied shallow soil layer riding on top of the liquefied soil. The observed damage and cracking to piles is often concentrated at the upper and lower boundaries of the liquefied soil layer where there is a sudden change in soil properties. A significant damage tends to occur to piles when the lateral movement is forced by a strong nonliquefied shallow soil layer than when the foundation is free to move laterally and the forces acting on them are limited by the strength of the liquefied soil. Peak ground deformations can occur either during or toward the end of shaking, depending on the magnitude of transient ground movements during the lateral spreading process.