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

Abstract

Earthquakes occur frequently in the Loess Plateau area, which result in damage to loess due to the disturbance of multiple cyclic loading. In this paper, the historical earthquake process is simulated by pre-dynamic loading treatment on undisturbed loess samples. Then cyclic tests are carried out on these treated samples to study the later liquefaction responses with different initial water content. The undisturbed sample is relative to the remold sample instead of the samples without disturbance. Results show that the axial deformation and pore pressure ratio of treated loess samples with initial water content of 5% are larger than those without treatment. For samples with initial water content of 10% and 15%, the cycle number required for liquefaction increases after treatment, but pore pressure ratio is between 0.18 and 0.36, which is less than the 5% water content samples. It means that liquefaction will have been formed before the excess pore pressure increases to large values. Combined with microstructural analysis, it is found that pre-dynamic treatment causes earthquake damage zone in loess with water content of 5%, which results in lower liquefaction stress ratio than non-treated ones. As for samples with water content of 10% and 15%, the internal voids become smaller and fine particles move into the gaps between large particles after treatment, resulting in denser structure which is hard to be liquefied. However, the increasing dynamic stress will aggravate the deterioration of loess at the water content from 5 to 15%. The changes of microstructure of loess samples are vulnerable to the dynamic stress amplitude and water sensitivity.