Liquefaction resistance of fibre-reinforced silty sands under cyclic loading

Whether the so-called double porosity in soils with a loose and natural packing state is a concept with real-world implications is a fundamental yet controversial question in the study of cyclic undrained shear behaviour of fibre-reinforced silty sands. An attempt is made here to clarify the question by means of particle-level modelling combined with 41 undrained cyclic triaxial shear tests. The study shows that the initial Random Loose Packing changes to Random Close Packing and then Close Packing with silt content increments. The transition from random to close packing occurs at a threshold silt content which is relatively lower in coarser sands. For sands with 40% silt content. Irrespective of fine content, fibres tend to sit deep into the silt pellets and encrust the macro-pore spaces. Generally, increasing fibre content leads to an increase in the average number of contacts per particle, dilation and easier dissipation of excess pore water pressure, a decrease in contact forces and improved liquefaction resistance. For sands with >40% silt content, effectiveness of fibre reinforcement diminishes with increasing sand median size. •Packing state of sand changes from RLP to RCP with increasing silt content to 20%.•Packing state of sand changes from RCP to CP with increasing silt content to 40%.•The efficiency of fibres in sand with >40% silt content may be compromised for sands larger than a critical size.•The onset of liquefaction in silty sands mixed with fibres is less sudden.•Fibre in silty sands relax the liquefaction risk through enhanced coordination number and rapid pore pressure dissipation.