VALUATION OF EARTH PRESSURES ACTING ON FOUNDATIONS DURING STRONG

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The field performance of buildings during recent catastrophic earthquakes is summarized, with emphasis placed on the effects of ground failure, nonlinear site response, and dynamic and permanent ground displacement. In addition to in-situ lateral load on steel pipe piles, large-scale shaking table tests are conducted to study the effects of soil-pile-structure interaction including those of nonliquefied crust overlying liquefied soil and p-y behavior of piles on pile performance. It is shown that : (1) the p-y behavior is affected by such factors as the pore pressure ratio, relative displacement of soil and pile, and soil density ; and (2) the total earth pressure acting on embedded foundation is induced mainly by the relative displacement between soil and foundation. Back-analysis is conducted for well-documented case histories of pile foundations to estimate the scaling factors for p-y springs of laterally spreading soils. The analytical results show that both the coefficient of the horizontal subgrade reaction of piles and the maximum reaction force of laterally-spreading soils are 0.05-0.2 times those of non-liquefied soils, consistent with the shaking table test results. Both effective stress and simple p-y analyzes, which incorporate the above findings, are conducted for several buildings that suffered various patterns of damage during soil liquefaction in the 1995 Hyogoken-Nambu earthquake. A comparison of the computed results with the filed observation indicates that both analyzes are cap able of discriminating damaged from undamaged foundations as well as of estimating the damage portion and severity with a reasonable degree of reliability.