ABSTRACT:

Damage to pile foundations due to liquefaction-induced ground flow during past earthquakes is reviewed. Then, studies of the behaviour of pile and raft foundations in liquefied and flowed ground are surveyed, and current design methods for foundations introduced. Although several design methods have been proposed recently, it is concluded that that further studies are necessary to establish definitive methods for the design of piled foundations in liquefiable ground.

1. INTRODUCTION

The liquefaction of loose sandy ground during earthquakes often causes severe damage to structures, for example, through the settlement of buildings induced by loss of soil strength. Moreover, if the ground has a gentle slope or faces a waterfront, the liquefied ground tends to flo\v, often causing extreme damage such as the collapse of pile foundations. The surest way to avoid damage is by improving the sandy soil so it will not liquefy, by densification or cementation methods. For example, the use of sand compaction piles, dynamic compaction, compaction grouting and deep cement mixing methods can prevent the occurrence of liquefaction. Furthermore, if the design input earthquake motion is very strong, it is difficult to prevent the occurrence of liquefaction by some soil improvement methods. For this situation, and as an alternative to costly soil improvement, it is desirable to develop alternative, more rational, design methods in which the occurrence of liquefaction is accepted but the structure is designed to survive it without damage. Some methods for the design of pile foundations in liquefied ground had already been developed before the 1995 Hyogoken-nambu (Kobe) earthquake in Japan. However, as many pile foundations suffered severe damage due to liquefaction and liquefaction-induced ground flow during the Hyogoken-nambu earthquake, the mechanisms of damage and design methods have been studied more intensively since then.

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