The effect of carbonaceous fines on the cyclic resistance of poorly graded sands

Abstract

The potential damage to man-made structures associated with earthquake-induced liquefaction has been demonstrated in catastrophic fashion over the past 40-50 years. The phenomenon of liquefaction of relatively clean, poorly graded, sands is well understood. However, the same cannot be said for cases when finegrained materials are present within the sand matrix. A resolution of what appears in some reported studies as conflicting observations related to the effect of fines on cyclic resistance is of concern, particularly for land reclamation projects and sea fills where the material source is variable and may contain significant levels of fines. The nature of the fines themselves may have a measurable effect on the matrix behavior. The work presented herein explores the effect of silt and clay-size carbonaceous fines on the liquefaction susceptibility of sand. The choice of fines was guided by the conditions associated with the Lebanon coastal reclamation projects, where limestone/marlstone quarry source materials are dominant. The results obtained confirm the significant effect of fines on the cyclic resistance. They also confirm the existence of a limit fines content and a plasticity index threshold and establish their effect on observed behavior.

Influence of Non-Plastic Fines on the Response of a Silty Sand to Cyclic Loading

“…Traditionally, the in‰uence ofˆnes content on the cyclic resistance ratio (CRR) of a silty soil has been studied by carrying out tests at constant void ratio, at constant sand skeleton void ratio, or at constant relative density, exclusive of each other, and results are usually plotted in terms of cyclic resistance ratio against silt content (e.g., Polito and Martin, 2001;Sadek and Saleh, 2007). Instead, Fig.…”

“…For example, Singh (1994) found that at constant relative density, the cyclic resistance ratio decreases with increasingˆnes content, while Polito and Martin (2001) found that the cyclic resistance ratio remains constant for values ofˆnes content up to the LFC, after which it drops to a stable value about half of the initial CRR. Finally, Sadek and Saleh (2007) found that the cyclic resistance ratio initially increases up to a particular silt content, after which it decreases with increasingˆnes content.…”

“…The addition ofˆnes to sand will result in a diŠerent grading and void ratio, and researchers have traditionally tried to maintain either the void ratio (e), or the relative density (RD), or the sand skeleton void ratio (es), constant in their research (e.g., Polito and Martin, 2001;Sadek and Saleh, 2007). This allowed the eŠect ofˆnes content to be isolated and used as sole variable.…”

“…Keeping the void ratio constant while increasing theˆnes content implies an increase or a decrease or an initial decrease followed by an increase in the density of the sand-silt mixture, which may in‰uence the result. A comparative study of the eŠects of non-plasticˆnes on the cyclic resistance of Ottawa sand by Sadek and Saleh (2007) showed that the cyclic resistance of sandy soils is better understood using a constant relative density (CRD) approach, if theˆnes content is below the limitingˆnes content, and a constant void ratio approach if theˆnes content is beyond the limitingˆnes content.…”

Undrained Cyclic Pore Pressure Response of Sand–Silt Mixtures: Effect of Nonplastic Fines and Other Parameters

“…Significant research have been carried out in the past by Silver and Seed (1971), Martin et al (1975), Dobry (1985), Wang and Kavazanjian (1989), Erten and Maher (1995), Polito (1999), Xenaki and Athanasopoulos (2003), Ueng et al (2004), Govindaraju (2005), Ravishankar (2006), and Derakhshandi et al (2007) on the pore water pressure generation of clean sands as well as sands with some amount of fines, but the manner in which the presence of fines in a sand affects the pore pressure response and in turn the cyclic resistance behaviour is a matter of discussion until now. Increase Amini and Qi 2000), decrease (Kuerbis et al 1988;Finn et al 1994) and initial decrease till limiting silt content and thereafter an increase (Polito and Martin 2001;Xenaki and Athanasopoulos 2003;Ueng et al 2004;Ravishankar 2006) in cyclic resistance with increase in silt content at a constant gross void ratio has been reported in the literature. At a constant relative density, Singh (1994) reported a decrease where as Polito and Martin (2001) reported an initial constant behaviour till limiting silt content followed by a drastic fall till a relatively stable level but Sadek and Saleh (2007) reported an initial peak and then a drastic fall in cyclic resistance with increase in silt content.…”