A behavioural framework for fibre-reinforced gravel

Abstract

The mechanical behaviour of granular materials is known to be influenced by the addition of fibres. However, most previous research has been carried out on materials with relatively small grains (sands), and its application to larger grains is not well documented. This paper reports an investigation into the mechanical behaviour of a fibre reinforced granular material having a relatively large grain size corresponding to 1/3 rd and 1/5 th scaled railway ballast. The investigation was carried out by means of triaxial tests incorporating a fullfield, image-based deformation measurement technique; this enabled detailed observations to be made of each triaxial test specimen during shearing. The test data demonstrate the benefits of random fibre reinforcement for aggregates having a relatively large grain size. Analysis taking into account the effect of fibre tension on the effective stresses experienced by the granular skeleton provides new insights into the mechanisms of reinforcement in larger sized granular materials.

Scaling relationships for strip fibre–reinforced aggregates

“…Following Jewell and Wroth (1987), Ajayi et al (2016) show that, if this fibre tension is accounted for by means of an additional effective stress acting on the soil grains, the stressstrain-strength behaviour of the granular matrix conforms to the established principles of soil mechanics. That is, the limiting corrected effective stress ratio is not altered by the addition of fibres, and the volume-related behaviour (particularly the increased ductility, reduced tendency to dilate, and the achievement of a peak stress ratio) is consistent with the increase in the void ratio caused or enabled by the fibres.…”

“…where emax and emin are the maximum and minimum void ratios for the unreinforced scaled ballast. As noted by Ajayi et al (2016), this means that values of ID for the reinforced materials may be negative because of the disruptive effect of the fibres on grain packing.…”

“…Fibre orientation was mostly subhorizontal, generally within the range of ±30° to the horizontal plane reported by Diambra et al (2008). The maximum and minimum void ratios (emax and emin) achievable using the methods of compaction and placement described by Ajayi et al (2016) increased with increasing Vfr, indicating that the addition of fibres interferes with the packing of the grains. This corroborates the findings of others including Michalowski and Zhao (1996), Ibraim and Fourmont (2007) and Dos Santos et al (2010).…”

“…where Aα and Bα are constants for a given combination of granular material, fibre type, fibre geometry and fibre content (Ajayi et al, 2016). The fibre/grain interaction factor α must be in the range 0 ≤ α ≤ 1.…”

“…The corrected radial (lateral) stress on the granular skeleton, denoted σ′′3, is then (Ajayi et al, 2016) …”