Cyclic Behaviour of Reinforced Sand-Fines Mixtures With Upcycled Rubber: Micro-Scale Considerations

The use of discarded tire in sand to mitigate liquefaction has received much recent interest. Most of the published research addresses the dynamic response of compacted tire-reinforced soils. Whilst compaction is indeed an integral part of remediation of liquefiable soils, prospects of safeguarding coarse soils against softening and liquefaction in their naturally loose state are remain a matter of interest. Loose soils provide network of pore spaces that facilitate conveyance of water and provide space for living flora and fauna, contributing to the health of wider ecosystem. The relatively high elasticity of shred tire—or Granulated Rubber (GR), term used in this manuscript—will have more substantial role in dynamic response of soil in its loose state. The unknown interaction of GR, sand and fines fraction in loose soils under undrained dynamic load remains a barrier to the use of GR (and elastic substances alike) in improvement of coarse soils in their loose state. This paper reports on findings from 36 undrained stress-controlled cyclic triaxial shear tests on uncompacted, naturally loose, silt—sand—GR composites with void ratios ranging from 0.42 to 0.81. Silt content varies between 0 and 50 wt% and GR varies in mead size, hence elasticity. A micro- to macro- approach is adopted to interpret findings. The potential for liquefaction increased with the addition of silt, reaching maximum at 33% silt content, as silt particles clump together to form load-bearing pellets that facilitate particle reorientation and flow. Very elastic GRs in sand generally eases the pore water pressure ratio, particularly when silt content is at an ‘intrinsic’ threshold. Hence, soil mixtures containing GR exhibit an enhanced capacity to absorb cyclic loading energy. Smaller size GRs enhance liquefaction resistance.