Evaluation of the Seismic Behavior on Sandy Ground with Built-Up Pore Water Pressures by Effective Stress Analysis

It is important to consider the non-linear behavior of the soil in evaluating the seismic behavior of the ground during the large ground motion. Pore water pressures, in the order of 75% of the initial mean confining pressures, were observed at the liquefaction observation sites near the Lake Utonai in Hokkaido, Japan during the 1993 Kushiro-oki earthquake. In the current study, effective stress analysis and total stress non-linear analysis were carried out incorporating both strain-dependent non-linearity and non-linear built-up of pore pressures. The following conclusions were reached: (1) Seismic behavior of the ground, acceleration of the surface ground, transfer functions etc., obtained from the effective analysis were sufficient to predict the observed records; (2) It was found from these analyses that shear strain was reached to 1 or 2x10-3 and pore water pressure ratio was built up to between 0.2 and 0.4 during the earthquake; (3) The amplitude and phase of the acceleration at the ground surface by effective and total stress analyses agreed well; and (4) The influence of the excess pore water pressure on the seismic behavior of the ground surface is not so significant when the excess pore water pressure ratio was less than 0.4 in general.