Soil-Pile-Structure Interaction During Liquefaction

An analytical method is presented for evaluating dynamic response of soil-pile-structure system during soil liquefaction. The method consists of a modified Penzien\u27s model combined with an effective stress analysis for free-field soil response and a horizontal subgrade reaction model which connects free field response with pile-structure response. Shaking table tests are conducted to study the effectiveness of the proposed procedure. A model sand deposit-pile-structure system is constructed in a large container which can permit shear deformation of the soil. Soil density, pile diameter, pile rigidity, and input motion are controlling variables in the tests. Analysis is made for both liquefied and non-liquefied cases, and the results are compared with the measured values. The analytical results including the time histories of excess pore water pressures, accelerations, and displacements, and the Fourier spectra of the ground surface and the pile head, are all in good accord with the observed values, showing that the proposed analysis is effective

Considerations to Damage Patterns in the Marina District During the Loma Prieta Earthquake Based on Rayleigh Wave Investigation

Rayleigh wave investigation is made in the Marina District to study geotechnical factors controlling the damage patterns in the Loma Prieta earthquake. A portable system has been developed for determining a Rayleigh wave dispersion curve based on the measurements of artificially induced ground vibration or microtremor. Five sites are selected along a line crossing the hydraulic fill zone in which structures and/or buried utilities were significantly damaged. An inverse analysis on the measured dispersion curves results in a cross section of shear wave velocity profiles in the District. Site amplification and liquefaction potential of each site are estimated and discussed based on the Vs-profiles. It is shown that soil liquefaction is likely to have occurred throughout the fill zone, and that the predominant period of ground motions in the zone of structural damage is longer than and closer to the natural period of structures with soft first story than that in the non-damaged zone. These results appear to be consistent with the damage patterns in the District, indicating that the proposed investigation is effective for seismic zonation