Effect of pre-dynamic loading on static liquefaction of undisturbed loess

Static liquefaction can make the loess unstable when the shear stress subjected to a monotonic loading exceeds the undrained peak shear strength of undisturbed saturated loess. It is a phenomenon in the failure of soil deposits caused by a sudden increase of pore water pressure accompanied by large deformations and loss of effective stress that can make soils behave like flowing liquids. In general, the static liquefaction is influenced by confining pressure, microstructure and particle size of the undisturbed loess. The composition and particle size of loess are not easy to be changed, but it is not the case for microstructure during the earthquake. A few scholars focused on the characteristics of static liquefaction when the natural loess was disturbed by pre-dynamic loading. The deviator stress, pore pressure, effective confining pressure of undisturbed loess will respond differently to liquefaction if the loess experienced pre-dynamic loading. This study examined static liquefaction phenomenon in saturated undisturbed loess considering the effects of pre-dynamic loading and confining pressure. Pre-dynamic loading tests with different peak ground acceleration (PGA) showed that the cumulative strain is in the range of 0.019–0.189% under the conditions of PGA = 0.15g, PGA = 0.30 g, PGA = 0.40 g, respectively. Undrained static triaxial compression tests at three different confining pressures (100, 150, and 200 kPa) were implemented on undisturbed loess samples. Static liquefaction was observed at confining pressures of 100 kPa and 150 kPa with different pre-dynamic loadings, and the liquefaction potential of the undisturbed loess decreased with the increases of confining pressure. Loess specimens treated with pre-dynamic loading were easier to liquefy than the samples without pre-dynamic loading treatment. Samples treated with pre-dynamic loading exhibited higher excess pore water pressure than those without pre-dynamic loading treatments. Therefore, the internal friction angle and cohesive force were 5.13%∼15.04% and 26.44%∼82.04% lower than untreated loess. It reveals that the normalization between the maximum and the minimum principal stresses can be used to quantify the liquefaction potential of undisturbed loess.