Abstract
The frequency of ground motions during earthquakes is typically in the order of a few hertz. As the earthquake-induced liquefaction of soils is widely assessed by performing laboratory tests, it is necessary to consider various loading frequencies generated by real earthquakes. The effect of loading frequency has been studied by cyclic triaxial tests; however, it has rarely been investigated by cyclic direct simple shear tests, which are more similar to the cyclic loading conditions associated with earthquakes. In this study, a series of cyclic direct simple shear tests were performed on clean sand with a relative density (Dr) of 40% (loose sand) and 80% (dense sand), obtained from Nakdong River. The parameters considered are the initial vertical effective stresses (σv0′ = 50, 100, and 200 kPa) and the loading frequencies (f = 0.05, 0.1, 0.5, and 1 Hz) to evaluate the effect of the loading frequency on the liquefaction prediction of clean sand. The results showed that the liquefaction resistance of the sand increases with the increase in the loading frequency, regardless of the initial vertical effective stress and relative density. When the loading frequency increased from 0.1 to 0.5 or 1 Hz, the maximum increase in the cyclic resistances were 15%, and 19% for loose and dense sand, respectively. For a given loading frequency, the liquefaction resistance of the sand decreased when the initial vertical effective stress increased.
Highlights
The frequency of a seismic excitation, varying mostly from 0 to 15 Hz [1], indicates that loading frequency is an important factor influencing the liquefaction behavior of soil layers
The effect of the loading frequency for the liquefaction resistance of sand has been studied for a wide range of loading frequencies from 0.05 to 12 Hz, mostly by conducting cyclic triaxial tests on medium saturated sand, and failure criteria based on the axial strain and excess pore
Note: initial vertical effective stress; relative density after consolidation (Drc ); loading frequency (f ); cyclic resistance ratio corresponds to liquefaction at 15 cycles (CRR15 ); the percentage increase in cyclic resistance at 0.1, 0.5 and 1 Hz relative to the cyclic resistance at 0.05 Hz
Summary
The frequency of a seismic excitation, varying mostly from 0 to 15 Hz [1], indicates that loading frequency is an important factor influencing the liquefaction behavior of soil layers. Some researchers, including Feng and Zhang [11] and Zhang et al [12], have examined the effect of the loading frequency on the cyclic strength in the frequency range 0.05–2 Hz and obtained a consistent result: in the cyclic triaxial test, the liquefaction resistance of sand increases significantly with an increase in the loading frequency, regardless of the relative density state Guo and He [13] investigated the influence of the loading frequency on saturated loose (Dr = 28%) and dense (Dr = 70%) sand at isotropic consolidation levels of 100 and 200 kPa by conducting cyclic triaxial experiments.
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