Influence of Loading History and Soil Type on the Normal Contact Behavior of Natural Sand Grain-Elastomer Composite Interfaces

Abstract

Recycled rubber in granulated form is a promising geosynthetic material to be used in geotechnical/geo-environmental engineering and infrastructure projects, and it is typically mixed with natural soils/aggregates. However, the complex interactions of grains between geological materials (considered as rigid bodies) and granulated rubber (considered as soft bodies) have not been investigated systematically. These interactions are expected to have a significant influence on the bulk strength, deformation characteristics, and stiffness of binary materials. In the present study, micromechanical-based experiments are performed applying cyclic loading tests investigating the normal contact behavior of rigid–soft interfaces. Three different geological materials were used as “rigid” grains, which have different origins and surface textures. Granulated rubber was used as a “soft” grain simulant; this material has viscoelastic behavior and consists of waste automobile tires. Ten cycles of loading–unloading were applied without and with preloading (i.e., applying a greater normal load in the first cycle compared with the consecutive cycles). The data analysis showed that the composite sand–rubber interfaces had significantly reduced plastic displacements, and their behavior was more homogenized compared with that of the pure sand grain contacts. For pure sand grain contacts, their behavior was heavily dependent on the surface roughness and the presence of natural coating, leading, especially for weathered grains, to very high plastic energy fractions and significant plastic displacements. The behavior of the rigid–soft interfaces was dominated by the rubber grain, and the results showed significant differences in terms of elastic and plastic fractions of displacement and dissipated energy compared with those of rigid interfaces. Additional analysis was performed quantifying the normal contact stiffness, and the Hertz model was implemented in some of the rigid and rigid–soft interfaces.

A study of wave propagation and stiffness anisotropy in anisotropically loaded granular material-synthetic fiber binary systems

“…Representative scanning electron microscope images of the two sands are given in supplementary Figure 1. Tian et al [66] examined the surface roughness (in terms of RMS) values of LBS and Blue sand and reported that Blue sand has grains with much rougher surfaces. RMS roughness values for LBS have been reported within a range of 0.20 to 0.45 μm [66][67][68], however Blue sand grains have, approximately, five to ten times higher RMS roughness compared with LBS [66].…”

Multi-Scale Study of the Small-Strain Damping Ratio of Fiber-Sand Composites

“…This material has origin a sedimentary rock and it consists, similar to Sydney sand, of quartz-based particles with an average size of 2 to 4 mm. Characterization of LBS particles has been presented in previous studies on sand grain contacts and sand-polymer-based contacts [56][57][58][59]. It is noted that the decision to use LBS particles for the grain-scale tests was that the micromechanical apparatus to test particle-to-particle contacts can accommodate sizes of grains, in general, between 1 and 5 mm, so it was preferable to use LBS than Sydney sand or White sand.…”

“…On the other hand, less microscopic energy dissipation (as hysteretic mechanism), may lead to the opposite result at the macroscopic level leading to increased bulk damping in the resonant column tests of fiber-sand mixtures. Especially for composite interfaces of sand particles sliding on polymeric surfaces, similar to that of sand-rubber composite systems, the response of sand-fiber-sand interfaces may have also been contributed by viscous mechanisms which cause an increased bulk energy dissipation [59,70]. In general, at small-strain perturbations, the results in the present study suggest a negative correlation between bulk damping and interparticle friction (which in turn, is related with the extended slip displacements in fiber-sand composite interfaces).…”

On the contact problem of soft-rigid interfaces: incorporation of Mindlin-Deresiewicz and self-deformation concepts

“…Given that LBS and CDV are two sands of extremely different morphological characteristics and properties (though both materials are "rough" in a contact mechanics context), the very similar friction values between LBS-rubber and CDV-rubber imply that the magnitude of surface roughness and other characteristics, which may contribute to the differences between the two sands, are very minor contributing mechanisms in the frictional behavior of the composite interfaces, and that rubber, which is a very soft material with viscous behavior controls the friction. It is noted that Tian et al [81] quantified the surface roughness of rubber particles and reported an average (RMS) value of approximately 2 microns, which is about 2 times greater than that of the CDV particles and 8 times greater than that of LBS. Despite some influence of the sand grain type, the study by [81] also reported a dominance of the rubber in the normal contact response of sand grain-rubber interfaces subjected to cyclic loading, with an approximate reduction of the normal contact stiffness of one to two orders of magnitude from the pure sand grain contacts to sand grain-rubber composite interfaces (note that the study by [81] investigated a broad range of sand particles, from LBS, to weathered granitic particles as well as grains from basaltic crushed rock).…”

“…It is noted that Tian et al [81] quantified the surface roughness of rubber particles and reported an average (RMS) value of approximately 2 microns, which is about 2 times greater than that of the CDV particles and 8 times greater than that of LBS. Despite some influence of the sand grain type, the study by [81] also reported a dominance of the rubber in the normal contact response of sand grain-rubber interfaces subjected to cyclic loading, with an approximate reduction of the normal contact stiffness of one to two orders of magnitude from the pure sand grain contacts to sand grain-rubber composite interfaces (note that the study by [81] investigated a broad range of sand particles, from LBS, to weathered granitic particles as well as grains from basaltic crushed rock).…”