Intergranular state variables and stress–strain behaviour of silty sands

Abstract

Relative contributions by the coarser and finer grains in a silty sand to its stress–strain response are affected by the intergranular matrix structure. The nature of this contribution is illustrated using an intergranular matrix phase diagram in terms of void ratio (e), fines content (FC), and intergranular and interfine void ratios (es and ef). New intergranular state parameters (ψs, ψf) and (es, ef) are introduced as state variables to characterize silty sands; es and ef dictate the steady-state characteristics of silty sand at low and high fines contents, respectively; ψs and ψf reflect the plastic compressibility characteristics at low and high fines contents, respectively. Using these state variables, the anticipated stress–strain–strength behaviour of silty sand in comparison to that of the host sand is presented. Similar stress-strain behaviour is expected at the same es and initial confining stress σ′c, with a few exceptions. At a constant void ratio e, es increases while ef decreases with addition of fines; a silty sand passes through different states. First, at low fines content, es (< emax,HS, the maximum void ratio of the host sand, case 1), and high ef the stress–strain behaviour is primarily governed by intergranular friction between the coarser grains. The steady-state line (SSL) is primarily dependent on es and is fairly independent of σ′c; When compared at the same es and at the same σ′c(or at the same ψ or ψs), the silty sand and the host sand show similar (not identical) stress–strain behaviour; with addition of fines, as es increases, the collapse potential increases and the stress–strain response becomes weaker. Second, with further addition of fines, when es approaches or exceeds emax,HS, the SSL is influenced by es and σ′c. When es is near emax,HS (case 2), the stress–strain curves for silty sands are similar at the same es and the same σ′c (or at the same ψ or ψs), but different from and stronger than that of the host sand. At very loose states (es > emax,HS; case 3), the stress–strain curves, normalized with respect to σ′c, are similar at the same es (or at the same ψ or ψs). Third, with further addition of fines beyond a threshold value, ef becomes sufficiently low (case 4); the fines impart a significant influence, while the role of intergranular (coarser-grain) friction diminishes; the silty sand is expected to behave similarly (not identical) to the host fines at the same ef and ψf ; at this stage, with further addition of fines, the collapse potential decreases.

The Effect of Fines on Critical State and Liquefaction Resistance Characteristics of Non-Plastic Silty Sands

“…For mixtures with highˆnes contents, when the sand grains become isolated (VSAND may be ignored), the interne void ratio, ef, may be a more appropriate parameter to be used (Thevanayagam and Mohan, 2000):…”

Mechanisms of compression in well-graded saprolitic soils

“…Coop and Lee 1993), some uncertainties still remain in describing the behaviour of binary mixtures (e.g. Thevanayagam and Mohan 2000). For example, there is agreement (e.g.…”

“…However, it is less clear what this value of fines should be for different soils (Zuo and Baudet 2015) and how the nature of the fines influences the mechanics of compression. The approach proposed by Thevanayagam and Mohan (2000) suggests using the traditional definition of void ratio at the two mixture extremes and an inter-granular or inter-fine void ratio for intermediate cases, depending on whether the mechanics are fines or coarse grain-dominated, but it remains rather subjective when to use one definition or the other as the transitional fines content is highly variable and difficult to predict (Zuo and Baudet 2015). This type of approach may also only be used if the particle size distribution is binary and there is sufficient separation of the two grading sizes.…”

Influence of grain shape and gradation on the shear behavior of sand mixtures

“…The properties of these soils, which are called as intermediate soils, vary because of the density and mixture content. Difficulties arise in understanding their stress-strain behaviour, compression mechanism, and liquefaction potential [1][2][3][4][5][6][7][8][9][10][11]. For example, Vallejo and Mawby [12] reported that shear strength of the clay-sand mixtures is fully controlled by the sand below 25% of fines content.…”