The 1995 Hyogoken-Nambu earthquake caused widespread liquefaction on the reclaimed islands in Kobe. The surrounding quay walls moved significantly towards the sea leading to horizontal movement of the soil behind the quay walls. Investigation of the piles installed in the reclaimed islands clearly showed the need for piles in such grounds to be designed taking into account the effects of lateral spreading of liquefied soils. The present study is aimed at establishing a simple design method for pile foundations subjected to such lateral spreading. A series of centrifuge tests were conducted to this end. Pile-to-wall distance, the thickness of non-liquefied layer, and the input earthquake motion were chosen as experimental variables, and their effects on pile behavior are discussed. The results show that the presence of the non-liquefied layer at soil surface and pile-to-wall distance play a very important role in the pile response. The non-liquefied layer seems to move as one unit towards the sea. A subsequent simple elastic analysis shows that the reduction in soil modulus in the non-liquefied layer near the quay wall may be an important aspect in estimating the pile response.

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Improving the ground beneath or beside existing structures is one of the most effective countermeasures against structural damage caused by seismic motion of the ground. Economical and mobile methods will be in high demand in Japan where seismic events with greater intensity are anticipated in the near future. The authors have developed a new in-situ soil mixing method using collapsible/expandable mixing blades and a special monitoring/auto-control system. This paper first describes the new technique in comparison with conventional soil mixing methods and describes the results of field tests. Lastly, an actual application is described in which a slope of loose deposits filling a valley is improved with inclined soil columns.

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