The mitigation of liquefaction potential of sand using synthetic fibres with rough surfaces

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. ru=1), and thus the sand’s resistance to cyclic liquefaction is improved. The imposition of initial deviator stress (qs) strengthens the beneficial effect of fibres. When the cyclic stress ratio (CSR) is 0.2 and fibre content (FC) is 0.5%, the qs of 29kPa increases the cycles to ru=1 by 1816.8% in loose sand than that when qs=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.