Viscous Properties of Granular Materials Having Different Particle Shapes in Direct Shear

Abstract

The viscous properties of air-dried relatively poorly-graded granular materials having diŠerent particle shapes were evaluated by performing a series of direct shear (DS) tests. The applied loading histories include repeated step changes in the shear displacement rate (• s) or repeated sustained loading stages during otherwise monotonic loading (ML) at a constant • s under constant vertical stress. Test results of an angular gravelly soil (i.e., Chiba gravel-a) obtained from the present study and those of a wide variety of poorly-graded granular materials (i.e., glass beads and natural sands including Toyoura, Hostun, Silica No. 6a, Ticino, Silver Leighton Buzzard, Ottawa, Albany and Monterey sands) previously obtained by the authors are analysed. The viscous properties of granular materials can be adequately described by three basic parameters: i.e., the rate-sensitivity coe‹cient, the residual rate-sensitivity coe‹cient (or their ratio, i.e., the viscosity-type parameter) and the decay parameter. These parameters, as well as the viscosity type (i.e., Isotach, Combined, TESRA and P&N), are strongly aŠected by particle shape as quantiˆed in terms of the degree of particle angularity while being rather independent of particle size. The creep deformation that takes place by sustained loading increases with an increase in the shear stress level, and it also increases with changes in the viscosity type associated with an increase in mainly the particle angularity and partly the coe‹cient of uniformity. The various viscous property types and transitions among them can be described by a single general equation incorporating these parameters. A non-linear three component model incorporating this general equation can simulate very well all of the various viscous responses observed in the DS tests referred to in the paper.

Effect of Particle Shape on the Mechanical Behavior of Natural Sands

“…Figure 3 shows good agreement between values of R for some soils as calculated by Yoshimoto et al (2012) and the SAGI number, while Figure 4 shows that SAGI is also compatible with the Roundness factor proposed by Krumbein & Sloss (1969), as reported by Cho et al (2006). Finally, similar compatibility is observed with the values of degree of angularity as proposed by Lees (1964) for some soils reported in previous studies (Duttine & Tatsuoka, 2009), as shown in Figure 5. However, while the SAGI values were calculated from data based on many thousands of particles tested by the laser image analysis, the roundness measurements from all these previous studies were made on a much more limited number of particles (typically between 20-30).…”

Time-dependent behaviour of sand with different fine contents under oedometric loading

“…Regarding strain rate effects, granular soils exhibit very abundant and various effects. This was investigated by Tatsuoka et al (2002Tatsuoka et al ( , 2008, Di Benedetto et al (2002), Duttine and Tatsuoka (2009), Enomoto et al (2009) and Peng et al (2010). Different stress responses resulting from a sudden change of the strain rate are classified as 1.…”

A Generalized Backward Euler algorithm for the numerical integration of a viscous breakage model

“…The underlying soil-pile behaviour has been interpreted as a consequence of the interplay between several factors, such as the breaking down of arching effects during creep, the activation of dilation enhancing the shaft capacity, the alteration of the grain structure due to chemical reactions, and the extensive crushing around the pile. [8][9][10] While the time-dependent characteristics of soils compressed at low pressure have been explored in many experimental studies, [11][12][13][14] other experimental works have focused on the effect of fragmented particles on the time-dependent characteristics of granular assemblies. 15,16 These studies have covered a wide range of experiments at different scales in which both the single particle [17][18][19] and the collective sample behaviour have been investigated.…”