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

Abstract

The use of polypropylene fibers as a geosynthetic in infrastructures is a promising ground treatment method with applications in the enhancement of the bearing capacity of foundations, slope rehabilitation, strengthening of backfills, as well as the improvement of the seismic behavior of geo-systems. Despite the large number of studies published in the literature investigating the properties of fiber-reinforced soils, less attention has been given in the evaluation of the dynamic properties of these composites, especially in examining damping characteristics and the influence of fiber inclusion and content. In the present study, the effect of polypropylene fiber inclusion on the small-strain damping ratio of sands with different gradations and various particle shapes was investigated through resonant column (macroscopic) experiments. The macroscopic test results suggested that the damping ratio of the mixtures tended to increase with increasing fiber content. Accordingly, a new expression was proposed which considers the influence of fiber content in the estimation of the small-strain damping of polypropylene fiber-sand mixtures and it can be complementary of damping modeling from small-to-medium strains based on previously developed expressions in the regime of medium strains. Additional insights were attempted to be obtained on the energy dissipation and contribution of fibers of these composite materials by performing grain-scale tests which further supported the macroscopic experimental test results. It was also attempted to interpret, based on the grain-scale tests results, the influence of fiber inclusion in a wide spectrum of properties for fiber-reinforced sands providing some general inferences on the contribution of polypropylene fibers on the constitutive behavior of granular materials.

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

“…Understanding of the bulk response of granular (and composite) materials, necessitates an investigation of their microscopic behavior such as grain contact parameters as multi-scale studies would suggest [42,[72][73][74]. For this purpose, in order to enrich the discussions from the wave propagation experiments, an additional set of microscopic (grain-scale) tests was conducted in the present study, in which case, as mentioned earlier in the paper, Sydney sand was replaced with LBS.…”

“…A similar approach as the one described by Li et al [42] was used to prepare the sand-fiber samples for the grain-scale tests. Sizes of around 1-2mm particles from LBS and Blue sand were used for these experiments and the fibers were placed on the lower grain, prior to bringing the upper grain downwards so that to apply the normal load to the contact.…”

“…A theoretical illustration on the influence of soft synthetic (polymeric) inclusions at the contacts of sand grains is given in Figure 17. Because of the softer and visco-elastic behavior of synthetic inclusions, apart from their contribution in altering the normal contact response of the interfaces within the granular system, also cause increased energy dissipation as the multi-scale test results by Li et al [42] showed on sand-fiber composites. In specific, the study by [42] focused on measurements of material damping at the macroscopic level through resonant column tests, and the grain-scale response of the interfaces (in the tangential direction) at the small scale through microscopic experiments.…”

“…Because of the softer and visco-elastic behavior of synthetic inclusions, apart from their contribution in altering the normal contact response of the interfaces within the granular system, also cause increased energy dissipation as the multi-scale test results by Li et al [42] showed on sand-fiber composites. In specific, the study by [42] focused on measurements of material damping at the macroscopic level through resonant column tests, and the grain-scale response of the interfaces (in the tangential direction) at the small scale through microscopic experiments. This visco-elastic behavior and significant energy dissipation at the interfaces was also supported by the micromechanical tests of Tian et al [66] on elastomer-sand grain contacts.…”

“…Binary granular materials including sand-fiber composites, display significant complexity in their behavior with competitive mechanisms to be encountered with respect to energy transport and dissipation as recent theoretical and experimental studies have shown [40][41][42]. This adds further difficulties in the constitutive modeling of these systems compared, for example, to the analysis of soil-planar block interactions.…”