Stochastic Analysis of Liquefaction Under Earthquake Loading

Liquefaction of sand deposits during earthquakes is studied as a problem of random vibration of nonlinear-hysteretic systems. The random vibration results lead to the determination of the mean and standard deviation of the strong-motion duration of a random seismic loading with a given intensity that causes liquefaction. These statistics are used to define the seismic resistance curves against liquefaction in the deposit. It is assumed that liquefaction occurs when the excess pore pressure becomes equal to initial effective overburden pressure, i.e., when the shearing stiffness of the sand deteriorates to zero under repeated alternate shaking. The random vibration results, together with the results from the uncertainty analysis of the soil properties, are also used to calculate the reliability of sand deposits against liquefaction under a random seismic loading with given intensity and duration. These conditional reliabilities, and the probabilities of all significant seismic loadings for the site over a specified time period, are then combined to obtain the lifetime reliability against liquefaction.National Science Foundation Grants CEE 80-02584 and CEE 82-1372