دانلود رایگان مقاله انگلیسی اثرات ذرات کوچک بر مقاومت روانگرایی لرزه ای خاک - اشپرینگر 2018

Abstract

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 lm), clay particles (0.1–5 lm), 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.

4 Conclusions

This paper reviewed the recent studies of small particles on soil liquefaction resistance, and several conclusions can be drawn:

1. The particle size changes associated with adding non-low plastic fine particles to ultrafine particles, and these particles have a huge influence on soil behaviors. The existence of non-low plastic fine particles will decrease liquefaction resistance. In fact, the smaller the fine particles, the lower of Fc that corresponds to the minimal liquefaction resistance. However, for ultrafine particles, the liquefaction resistance will increase, even at very low content. Clay particles show both effects, depending upon on the Cc and clay mineralogy.

2. From fine to ultrafine particles, the effect of small particles changes from mechanical friction to hydration adsorption, which makes the mechanisms very different from each other. In short, in micrometer scale, fine particles mainly affect the interaction of sand particles while in nanometer scale, ultrafine particles mainly affect the pore fluid properties.

3. There are still a number of research challenges for small particles. Clearly, relative density may not be a suitable parameter for high Fc soils, because there is no test method to determine relative density at high Fc. In addition, fine particles shape, the effects of plasticity of the clay particles, and the long-term reinforcement performance of ultrafine particles require further attention.

4. The effects of fine clay particles on the seismic design codes and laboratory tests are inconsistent. In addition, the SPT may not be appropriate to evaluate soil improvement effect of ultrafine particles, because the tested counts cannot incorporate the properties change of pore water.