Effect of Liquefaction on Displacement Spectra

Abstract eng:
At present, the seismic design of structures is mainly based on the response spectra. The seismic responses for the deep foundations, the underground structures and structures with the long or high scale are dominated by soil deformation in general and in these cases, the displacement spectra is more significant than the acceleration spectra. Liquefaction is one of the important reasons for earthquake damages. The liquefied soils filter the high frequency parts of incident waves and while amplify the low frequency parts. The later effects are quite significant to the seismic design of above structures and little study, however, is conducted for the problem. The effect of liquefied soil layers on displacement spectra is discussed and the revised displacement spectra due to liquefaction are presented in the paper. The effects of liquefaction on the peaks of surface displacements, different frequency range of spectra and the regularity of the surface ground motion are investigated by seismic record analysis, numerical simulation and shaking table tests. The decreasing and increasing threshold of liquefaction are identified and the revised form of displacement spectra is constructed. The results here indicate: (1) For the uniform incidence of equal-amplitude, the liquefied soil layer amplifies the displacement amplitudes by 5 times to 25 times; (2) For the random seismic incidence, the liquefied soil layer enlarges the displacement amplitudes by a few times compared with the non-liquefied soil layer; (3) The amplification of the displacement spectra due to liquefaction begins at 1s and the most notable range is 2s-5s; (3) The amplification of the displacement spectra due to liquefaction is 0.1m-0.7m and increases with the increasing of intensity of the inputting waves.

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