Shear wave velocity and stiffness of sand: the role of non-plastic fines

Abstract

Current knowledge on the shear wave velocity (V s ) and associated stiffness (G 0 ) of sand is built mainly on the results of extensive laboratory studies on clean quartz sands. Often natural sands are not clean, but contain a certain amount of fines. The role of fines in altering the stiffness of sands is a matter of great concern, yet remains poorly understood. This paper presents an investigation into the problem through well-controlled laboratory experiments in conjunction with analysis and interpretation at the macro and micro scale. The laboratory experiments were conducted for a sequence of mixtures of clean quartz sand and crushed silica fines under saturated conditions, by the simultaneous use of the resonant column (RC) and bender element (BE) techniques. A broad range of states in terms of void ratio, confining stress and fines content was covered so as to obtain a comprehensive view on the effect of fines and the possible interplay with other factors. Both the RC and BE tests showed that G 0 tends to decrease continuously as the quantity of fines is increased and the reduction rates are similar; a similar stress dependence is also obtained for G 0 from both types of testing. Nevertheless, G 0 values obtained from BE tests are notably greater than those obtained from RC tests, and this effect of testing method is shown to be coupled with the sample reconstitution method. A new approach that allows unified characterisation of G 0 values for both clean sand and sand-fines mixtures is developed in a sound theoretical framework, thereby providing important insights into the various empirical correlations that involve G 0 (or V s ) in geotechnical engineering practice. A new micro-scale mechanism is also suggested for the observed effect of fines, which attributes the reduction of G 0 caused by fines to the decrease in the coordination number at an approximately constant void ratio.

Particle-scale insight into transitional behaviour of gap-graded materials – small-strain stiffness and frequency response

“…The ratio of the median particle diameters (D50) of the coarse and fine particles (χ) and the fines context (Fc = mass of fines/total mass) both determine the behaviour [4]. Yang & Liu [5] used mixtures of Toyoura sand and crushed silica fine (χ ≈ 4) and found that G0 dyn decreases as Fc increases up to 30%. They prepared the mixtures maintaining an equivalent range of global void ratios (e).…”

Laboratory Investigation of the Mechanical Properties of a Rubber–Calcareous Sand Mixture: The Effect of Rubber Content

“…The general procedure of the 1-D compression test followed the British Standard (BS 1377) [24]. In contrast, as there are no specified procedures for the resonant column test, we performed the test in accordance with the way prescribed in the literature [25,26]. In the compression test, a modified oedometric compaction cell was use, i.e., a 27.6 mm diameter cell that is 30 mm high, which can apply a maximum vertical load of 16 MPa (Figure 2a).…”

“…Note that the strain level involved in the resonant column test was in the order of 10 −5 or below; accordingly, the small strain shear modulus (G0) of the specimen was determined. Those interested in more detailed information can refer to Yang and Liu [26] and Liu et al [27] for more features about the resonant column technique. Figure 3 presents the results obtained for the rubber-sieved calcareous sand mixtures of different rubber contents and initial void ratios.…”

Shear wave velocity and stiffness of sand: the role of non-plastic fines

“…For comparison, Fig. 26 here presents the variation of parameter 1·2 0·8 Iruma sand (Iwasaki & Tatsuoka, 1977) Yunlin sand (Chien & Oh, 1998) Ottawa sand (Salgado et al, 2000) Toyoura sand, BE (Yang & Liu, 2016) Toyoura sand, RC (Yang & Liu, 2016) …”

“…Exponential relation between A and f c The authors (Yang & Liu, 2016), by using c = 2·17 for Toyoura sand (sub-round) with crushed silica fines in the empirical equation of Hardin and Black (1966), suggested that A deceases with increasing f c and can be presented by a simple exponential function of f c (their equation (4)). However, the A-f c relationship for a specific sand-fines mixture may not be applicable to another sand-fines mixture, as evident from the database of Rahman et al (2012) and presented as Fig.…”