Fiber-reinforcing technology involves adding discrete and tension-resistant fibers into soils to improve the mechanical properties of the soils. This study investigates the static liquefaction responses of the fibre-reinforced sand in loose states by performing the undrained triaxial compression tests. The feasibility of varied excess pore pressure ratios for assessing the liquefaction of fibre-reinforced sand also has been discussed. The test results reveal that the loose sand without reinforcement is highly susceptible to static liquefaction under undrained triaxial compression, while the inclusion of fibers prevents the development of static liquefaction in the sand samples. The presence of fibers significantly alters the effective stress path experienced by the sand skeleton and thereby influencing its liquefaction response. The conventionally defined excess pore pressure ratio (r(u)) based on the principle of effective stress may provide incorrect indications of liquefaction in fiber-reinforced sand. To address this, the study introduces the newly defined effective excess pore pressure ratio (r(u)') and the skeleton excess pore pressure ratio (r(u)(*)), which offer improved indications of liquefaction in reinforced sand. By invoking a constitutive framework based on the rule of mixture, the stress contributions of fibers are quantified. The skeleton excess pore pressure ratio takes into account stress contributions of the fibers and reveals how the external load is shared among the fibers, sand skeleton and the pore water. When r(u)(*) = 1 is attained, the effective mean stress carried by the sand skeleton drops to zero, resulting in liquefaction of the fiber-reinforced sand.
