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Adding discrete fibres to sand has been seen as a feasible technique to improve sand's strength as well as liquefaction resistance. Considering the anisotropic distribution of fibre orientations, the anisotropy in the liquefaction resistance of the reinforced sand is also introduced using fibres. Here, the triaxial compression and extension test results of unreinforced and fibre-reinforced sand in different density states are provided, from which the anisotropy in the liquefaction resistance of fibre-reinforced sand is demonstrated. Fibre reinforcement improves the liquefaction resistance of sand by introducing both the densifying effect and the confining effect. The inclusion of fibres increases both the slope and the intercept of the strength envelope in comparison with the unreinforced sand under triaxial compression, while the strength envelope is not affected by fibres under triaxial extension. Stress contribution of fibres makes the ESP of the composite under undrained loading reverse its direction to develop even though the phase transformation is absent. The stress ratio initiating the ESP reversal is irrespective of the fibre content but dependent on the density state under triaxial compression. Under triaxial extension, the stress ratio initiating the ESP reversal remains the same in the samples with varied density states and fibre contents. The mechanism correlating to the strength envelope and ESP reversal of the fibre-reinforced sand was demonstrated following a rule of mixture based constitutive modelling framework. By introducing an alternatively defined pore pressure ratio that incorporates the stress contribution of fibres, the liquefaction state of the fibre reinforced sand is reasonably assessed. Liquefaction remains absent in the sand once the fibres are mixed. The anisotropy in the liquefaction resistance of fibre-reinforced sand arises, as the predominant role played by the fibres to suppress the liquefaction is different when varied loading paths are involved, which is sourced from the anisotropic distribution of fibre orientations. [ABSTRACT FROM AUTHOR]

Mixing discrete fibres into sand is seen as a technique to suppress liquefaction. Here monotonic and cyclic triaxial tests were performed and the effect of fibres on mitigating the liquefaction potential of sand was examined. The results indicate adding fibres increases the sand's resistance against static liquefaction by introducing densifying and confining effects. The benefits of reinforcement on static liquefaction vary in tests involving different sand densities and loading paths. Under undrained cyclic loading, adding fibres increases the number of loading cycles leading to the unity of excess pore water pressure ratio (i.e. r u =1), and thus the sand's resistance to cyclic liquefaction is improved. The imposition of initial deviator stress (q s) strengthens the beneficial effect of fibres. When the cyclic stress ratio (CSR) is 0.2 and fibre content (FC) is 0.5%, the q s of 29kPa increases the cycles to r u =1 by 1816.8% in loose sand than that when q s =0. A wedge-shaped instability determined from undrained monotonic tests can roughly predict the onset of cyclic instability of sand. Well-tensioned fibres impose a great confining effect on sand skeleton under undrained cyclic loading, which alters the evolution of residual excess pore water pressure and stops the liquefied state in sand. • Fibre reinforcement introduces densifying and confining effects to suppress the sand's liquefaction. • Density and loading path affect the mitigation of sand's static liquefaction potential benefiting from fibre reinforcement. • A linkage between the initiation of instability under undrained monotonic and cyclic loading prevails. • Fibre reinforcement increases the number of cycles to cause r u =1 under undrained cyclic loading. • A great confining effect alters the evolution of residual excess pore water pressure and the liquefaction state of sand. [ABSTRACT FROM AUTHOR]