The negative skin friction (NSF) of pile foundations is one of the most important factors in triggering building subsidence. To study the mechanism and development of the NSF over time, four methods have been used: theoretical calculations, field tests, model tests, and numerical modeling. To address the difficulty of sampling prototype soft soils in model tests, this study uses a dynamic triaxial instrument to select a similar material ratio that can effectively simulate the dynamic properties of the prototype soft soil as a soft soil layer, and input sine waves with different frequencies and peak ground acceleration (PGA) for shaking table tests to investigate the effects of frequency and PGA on the development of the distribution of NSF and the location of the neutral point of the pile foundation. The test results show that the pile NSF is mainly distributed in the upper part of the pile under horizontal sine wave loading, increases rapidly from 0 to 5 s, and stabilizes after 5 s. Its magnitude is influenced by the sine wave frequency and PGA, and the effect of PGA on the NSF is more significant. In addition, the pile neutral point position shifts downwards with increasing sine wave frequency and PGA, but the downwards shift is not significant.
Soft soils are characterized by high sensitivity, low strength, and susceptibility to seismic subsidence. In this study, nonlinear dynamic finite element analysis was performed using the OpenSees numerical simulation method to evaluate the seismic subsidence response of soft soil sites to ground motions. Higher peak acceleration of ground motion was found to enhance the degree of uneven seismic subsidence, depth of the seismic depression, and damage to the horizontal surface. The frequency characteristic of ground motion is another factor that influences the seismic subsidence of soft soil. Ground motions with low-frequency contents or high amplitudes lead to a more pronounced seismic subsidence of soft soil, particularly in the case of ground motion that exhibits frequency predominantly close to one of the soil sites. The findings of this study expand the current understanding of seismic subsidence of soft soil.
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