The effects of small particles on soil seismic liquefaction resistance: current findings and future challenges

The natural and artificial sand soils always incorporate other small particles, which makes the soil liquefaction resistance difficult to predict. The particle size may change from 10−5 m (e.g., fine particles) to 10−8 m (e.g., ultrafine particles), and the soil behaviors change dramatically when such particles are present. Newly reported soil liquefaction cases involving fine particles provide great challenges to seismic design codes. To make it clear, this paper reviewed effects of small particles on soil liquefaction in three different types. The non-low plastic fines (5–75 μm), clay particles (0.1–5 μm), and ultrafine particles (1–100 nm) are discussed, respectively. Many scholars found that liquefaction resistance decreased at first but increased as fine particles (non-low plastic fines or clay particles) were added. This phenomenon can be attributed to the lubrication effect of fine particles. However, when particles in nanometer scale, the strong bond between particles and hydration adsorption of nano-suspension improve liquefaction resistance. There are still many challenges to understanding the roles of small particles in liquefaction, for example, determining relative density for a high fine content, determining particle shape effect (e.g., aspect ratio, flatness, and particle roundness), as well as the long-term reinforcement performance of ultrafine particles. In engineering practice, it suggests that the seismic design codes address the effects of non-plastic fines in laboratory tests. As for some new liquefaction mitigation methods by ultrafine particles, we believe that the standard penetration test may not be appropriate to evaluate soil improvement effect, because the test results cannot reflect the properties change of pore water.