ABSTRACT:

Earthquake induced flow failures of saturated or partially saturated sloping ground have taken place in man-made earth structures during the past earthquakes. Conditions leading to such flow failures in infinite slopes with seepage water resting on stiff slopes were investigated by a series of dynamic centrifuge tests. The test parameters included soil density, underslopes angle, level of seepage water and shaking intensity. The test results showed that downslope deformation increased with decreasing soil density and there existed a threshold soil density below which flow failures could occur. The effects of increasing seepage water elevation and shaking intensity was insignificant, once flow started.

INTRODUCTION

During past earthquakes, road embankments constructed on mountain/hill side have experienced catastrophic flow failures. Such flow failures of road embankments were found in the 1968 Tokachi-oki earthquake (PWRI, 1971), the 1993 Kushiro-oki earthquake (PWRI, 1994) and the 1995 Hyogoken Nanbu earthquake (PWRI, 1997). In most of the cases, location of such sites are found wherein surface water or seepage water are likely to accumulate, which eventually causes the bottom layer of the target slope to be saturated with water. It is interesting to note that among eleven sites of road embankments which were severely damaged by the 1995 Hyogoken Nanbu earthquake; three were located at slope dips, six were partly submerged by pond water. However, in their model experiments, the observed permanent deformation was limited to continuous deformation with a shear strain level of at most 10 %, and no rupture failure was reproduced as observed in the fills during past earthquakes. This paper reports results of dynamic centrifuge tests that were conducted in order to reproduce the phenomena, thus to study the mechanism and to clarify the conditions for the flow failures to take place.

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