The application of disposable face mask fibers in the enhancement of the mechanical properties of cement-stabilized soils is rigorously examined in this study through performing several triaxial tests on fiber-reinforced sand-cement mixtures with varying contents of additives under different confining pressures. To this end, sand samples stabilized with different percentages of cement (4% and 8%) are reinforced with various contents of face mask fibers (0%, 0.25%, 0.5% and 0.75%). After seven days of curing, the fiber-reinforced stabilized specimens are subjected to a comprehensive series of consolidated drained (CD) triaxial tests with all-round pressures of 50, 100 and 200 kPa. The results generally show that the addition of mask fibers to sand-cement mixtures up to 0.25% increases their ultimate strengths; whereas further increase of fiber content is observed to have an adverse impact on the strength parameters of the composite. Therefore, 0.25% mask fiber inclusion is reported to be the optimum content, which constitutes maximum strength characteristics of the samples. The contribution of mask fiber addition to the variation of ultimate strength of stabilized mixtures is noticed to be more pronounced in the samples with higher cement contents under greater isotropic confining pressures. Moreover, with increasing the percentage of mask fibers, the failure strain of all stabilized samples increases, thus exhibiting more ductile behavior. Unlike for the samples containing relatively low cement contents (4% herein) where brittleness index is barely affected by the mask fiber content, this parameter significantly decreases with the fiber inclusion for the specimens stabilized with relatively high cement contents (8% herein). Secant modulus is also observed to experience a decreasing trend with the addition of mask fibers to the mixture; the trend which is more pronounced for samples containing higher cement contents. Finally, the internal friction angle and cohesion of cement-stabilized samples generally show increasing trends with the addition of mask fibers up to 0.25% and then reveal decrement. Overall, the combination of cementation and fiber reinforcement demonstrates a significant synergistic effect, resulting in notable improvements in the mechanical properties of fine sands.

The widespread usage of disposable face masks (DFM) during the COVID-19 pandemic has exacerbated waste management challenges, prompting an investigation into their potential reuse as a soil reinforcement material. Previous researchers have investigated the effect of mask fibres on pavement subbases and the environmental problems caused by these fibres. This study examines the mechanical properties of sandy soil enhanced with shredded and layered DFM under triaxial testing conditions, focusing on key parameters like shear resistance, elastic modulus, stress-strain characteristics, axial resistance, failure envelope, and brittleness index. Results show that adding DFM significantly improves soil cohesion, friction angle, shear strength, and peak deviatoric stress, especially at higher fibre contents and relative densities. However, increased DFM fibre content was associated with reduced elastic modulus, which stabilised in specimens with layered DFM, suggesting complex interactions between DFM content and soil mechanics. Concerns include potential void formation leading to asymmetric settlement and environmental issues on non-biodegradable fibre integration in soil. These findings highlight the need for meticulous mixture preparation, large-scale studies, and environmental assessments to evaluate the impact of using DFM in soil reinforcement, particularly for road construction and slope stabilisation. This research provides crucial insights into the potential of DFM for soil reinforcement.

An important drawback of the hypoplastic model is the inaccurate prediction of the sand behavior under undrained monotonic loading conditions. The model is not able to reproduce the limited liquefaction type response widely observed in undrained tests on loose sand, and it often underestimates the initial stiffness and hardening rate of sand during the shearing. To address these issues, three novel modifications are introduced into a basic hypoplastic model to enhance its undrained predictive capability. Firstly, a new factor is added to the nonlinear term of the model, allowing the simulation of a purely elastic response at the beginning of loading. By doing so, the model can accurately capture the initial stiffness and undrained effective stress path of sand. Secondly, the characterized void ratios are related to an evolving state variable, enabling the model to reasonably reproduce the limited flow response and quasi-steady state. Furthermore, a new term is incorporated into the deviatoric part of the strain rate to adjust the hardening rate of the model. The model performance for undrained loading is significantly improved through the above modifications, as evidenced by the good agreement between simulation results and experimental data for tests with varying densities and confining pressures.

Microbially induced calcium carbonate precipitation (MICP) technology is an emerging and environmentally sustainable method for improving the strength and stiffness of soil. Specifically, this innovative approach has gained favor in marine engineering due to the advantaged compatibility between precipitated calcium carbonate induced by MICP and coral sand. Sand containing fines is susceptible to liquefy. Whereas, the impact of fines contents on cyclic behavior of MICP-treated calcareous sand remains uncertain. Consequently, this technical note aims to investigate the liquefaction behavior of biocemented calcareous silty sand by conducting undrained cyclic triaxial shear tests and microscopic analysis. The results revealed the patterns of the excess pore water pressure curves and cyclic deformation characteristics as the fines contents increased. The liquefaction resistance of biocemented sand initially decreases with the addition of fines but subsequently exhibits an increasing trend. Microscopic analysis showed that at the cementation level with the cementation solution concentration of 1 mol/L, the calcium carbonate crystals are mainly attached to the surface of sand grains and this pattern does not directly affect the force chain.

The presence of fines can significantly influence the mechanical behavior of soils. In this study, a hypoplastic model is extended to simulate the stress-strain relationship of sand-fines mixtures. Firstly, three modifications are incorporated into the model to accurately simulate the effective stress path, hardening rate, and limited flow type response of sand during undrained loading. Additionally, a novel formulation is proposed to capture the critical state line of soil mixtures across a wide range of fines content. This formulation is then integrated into the characteristic void ratios of the hypoplastic model, enabling it to effectively consider the combined influence of void ratio, confining pressure, and fines content on the density state of the sand-fines mixtures. The predictive capability of the model is demonstrated through a comparison of simulation results and experimental data for undrained triaxial tests conducted under various conditions.