اثرات ذرات کوچک بر مقاومت روانگرایی لرزه ای خاک: یافته های فعلی و چالش های آینده The effects of small particles on soil seismic liquefaction resistance: current findings and future challenges

1 Introduction Since the Niigata and Alaska earthquakes in 1964, many researches have been carried out on soil liquefaction. Soil seismic liquefaction occurs due to the increase in excess pore water pressure of soil. It will cause huge disasters to human populations (Juang and Li 2007; Huang and Jiang 2010; Bhattacharya et al. 2011; Huang and Yu 2013). In studies of soil liquefaction, fine and ultrafine particles play an important role, because these small particles influence soil instability (Abedi and Yasrobi 2010), static shear strength (Yang and Wei 2012), and cyclic shear strength (Beroya et al. 2009). The size of small particles is about nano- and microscale (Otterstedt and Brandreth 1998), and it incorporates three different types of particles (from 1 nm to 75 lm) based on the review of this problem. In particular, the non-low plastic fines, clay particles, and ultrafine particles were considered as distinct categories because of their very different size and properties. The specific definition of particles size will be introduced in Sect. 2. The effects of fine particles on soil liquefaction have been known since the 1970s. A Chinese liquefaction susceptibility criterion was first proposed by Wang (1979). This famous criterion considers the effects of fine particles based on the observed failures following the 1975 Haicheng and 1976 Tangshan earthquakes. Seed and Idriss (1982) modified this ‘‘Chinese criterion,’’ pointing out that soil types and clay content (Cc) are crucial to liquefaction, since soils with clay fines (\5 lm) of more than 15% will not be liquefied. Seed et al. (1985) also found that fine particles (\75 lm) influence standard penetration test (SPT) blow counts (Fig. 1), with liquefaction resistance increasing with increasing fine content (Fc). Tokinatsu and Yoshimi (1983) came to the same conclusion for soils containing clay particles. Although it believes that the soils with high Fc or Cc will not liquefy, there are many cases of soils with high Cc that were reported to have liquefied during strong earthquakes (Tan et al. 2013). For example, soils containing 19% Cc were found to be liquefied in the Chi-Chi earthquake (Hwang and Yang 2001), as well as the Marmara (Turkey) earthquake (Bol et al. 2010). This has led to ongoing discussion of the roles of small particles in liquefaction. More recently, scholars have found that ultrafine particles (e.g., nano bentonite) inhibit the generation of pore water pressure, and those particles can be used to mitigate soil liquefaction (Gratchev et al. 2007; El Mohtar et al. 2008, 2013). In addition, there are many indices used to evaluate soil liquefaction resistance for soils containing clay particles, including Cc (Ghahremani and Ghalandarzadeh 2006), plasticity index (PI) (Boulanger and Idriss 2006), as well as the content of specific clay minerals (Beroya et al. 2009). In this paper, the effects of small particles on the liquefaction resistance were reviewed based on three different particles. In addition, we outline the research challenges related to working on soil liquefaction of soils containing small particles.