WHAT IS LIQUEFACTION

LIQUEFACTION Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water. This water exerts a pressure on the soil particles that influences how tightly the particles themselves are pressed together. Prior to an earthquake, the water pressure is relatively low. However, earthquake shaking can cause the water pressure to increase to the point where the soil particles can readily move with respect to each other. Earthquake shaking often triggers this increase in water pressure, but construction related activities such as blasting can also cause an increase in water pressure.

WHAT IS LIQUEFACTION

Japan, Niigata (1964) Earthquake

Türkiye Kocaeli Earthquake (1999)

USA San Fernando Earthquake(1971)

Japan Niigata Earthquake(2004)

Japan Niigata Earthquake (2004)

LIQUEFACTION Evaluation of Liquefaction Potential There is no risk FS = CRR / CSR A factor of safety greater than one indicates that the liquefaction resistance exceeds the earthquake loading, and therefore that liquefaction would not be expected. There is no risk

EVALUATION OF CSR Seed and Idriss (1971) formulated the following equation for calculation of the cyclic stress ratio: where amax = peak horizontal acceleration at the ground surface generated by the earthquake (discussed later); g = acceleration of gravity; svo and s’vo are total and effective vertical overburden stresses, respectively; and rd = stress reduction coefficient. z < 9.15m  rd = 1.0-0.00765z 9,15m ≤ z < 23.0m  rd = 1.174-0.0267z 23,0m ≤ z < 30.0m  rd = 0.774-0.008z z > 30.0m  rd = 0.5

LIQUEFACTION Evaluation of Liquefaction Potential

LIQUEFACTION Evaluation of Liquefaction Potential

LIQUEFACTION Earthquake induced Settlements in Saturated Sandy Soils The post-earthquake densification of saturated sand is influenced by the grain size and relative density of the sand, the maximum shear strain induced in the sand, and the amount of excess pore pressure generated by the earthquake. A number of procedures have been presented in the literature in the past 20 years to study the earthquake-induced settlement problem and they can vary from relatively complex non-linear dynamic computer models to simplified procedures that estimate the consolidation settlement from volumetric strain based on the cyclic stress ratio and normalized SPT-N value. Ishihara and Yoshimine (1992) developed a graphic representation to evaluate the post-liquefaction volumetric strain as a function of factor of safety against liquefaction, maximum shear strain and relative density.

LIQUEFACTION Earthquake induced Settlements in Saturated Sandy Soils H = H. v N1 = (N1)90