The mechanical behaviour of Fibre-reinforced sands (FRS) has been extensively studied, presenting improved mechanical properties compared to unreinforced soils. Many models have been developed to predict its general stress-strain behaviour. However, the use of double-phase models in FRS is still incipient. Double-phase models are advantageous because they can simulate the whole FRS and the behaviour of its individual components, soil skeleton and reinforcement. This paper uses a modified model for Municipal Solid Waste to reproduce the FRS mechanical response. Introducing a new hardening parameter and a dilatant zone allowed the model to reproduce FRS dilatancy. The model's variables are easily understood, allowing the reproduction of the mechanical behaviour of FRS formed by sands with void ratios ranging from 0.610 to 0.917 and mean grain size from 0.29 to 0.83 mm. The fibres' lengths varied from 12.5 to 51 mm. The results of triaxial and hollow cylinder torsional tests under different stress paths had their main characteristics (peak strength, post-peak behaviour, dilatancy and reinforcement effectiveness) well captured by the model. Predicted and experimental FRS's deviator stress usually differ by less than 15% and the model performance is equivalent or superior to other available models, even requiring fewer input parameters.

Loess is widely distributed in the northwest and other regions, and its unique structural forms such as large pores and strong water sensitivity lead to its collapsibility and collapse, which can easily induce slope instability. Guar gum and basalt fiber are natural green materials. For these reasons, this study investigated the solidification of loess by combining guar gum and basalt fiber and analyzed the impact of the guar gum content, fiber length, and fiber content on the soil shearing strength. Using scanning electron microscopy (SEM), the microstructure of loess was examined, revealing the synergistic solidification mechanism of guar gum and basalt fibers. On this basis, a shear strength model was established through regression analysis with fiber length, guar gum content, and fiber content. The results indicate that adding guar gum and basalt fiber increases soil cohesion, as do fiber length, guar gum content, and fiber content. When the fiber length was 12 mm, the fiber content was 1.00%, and the guar gum content was equal to 0.50%, 0.75%, or 1.00%, the peak strength of the solidified loess increased by 82.80%, 85.90%, and 90.40%, respectively. According to the shear strength model, the predicted and test data of the shear strength of solidified loess are evenly distributed on both sides of parallel lines, indicating a good fit. These findings are theoretically significant and provide practical guidance for loess solidification engineering.

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.