Soil erosion can be effectively controlled through vegetation restoration. Specifically, roots combine with soil to form a root-soil complex, which can effectively enhance soil shear strength and play a crucial role in soil reinforcement. However, the relationship between root mechanical traits and chemical compositions and shear performance and reinforcing capacity of soil is still inadequate. In this study, we determined the root chemical properties, performed root tensile tests and root-soil composite triaxial tests using two plants-one with a fibrous root system (ryegrass, Lolium perenne L.) and the other with a tap root system (alfalfa, Medicago sativa L.)-and calculated the factor of safety (FOS). The results revealed that the relationship between root diameter and tensile strength differed among different root characters. Holocellulose content and cellulose content were the main factors controlling the root tensile strength of ryegrass and alfalfa, respectively. The shear properties of the root-soil complex (cohesion (c) and internal friction angle (phi)) are correlated with soil water content (SWC) and root mass density (RMD). Root traits had a more substantial effect on c than phi, with significant differences in c between ryegrass and alfalfa at 7 % and 11 % SWC. The root-soil complex had an optimum RMD, and the maximum increase rates of c were 80.57 % and 34.4 %, respectively. Along slopes, sliding first occurs at the foot of the slope, thus demanding emphasis on protection and reinforcement. On steep gradients with low SWC, ryegrass strongly contributes to soil reinforcement, whereas alfalfa is more effective on gentle gradients with high SWC. The results provide scientific references for species selection for vegetation restoration in the Loess Plateau and a deeper understanding of the mechanical mechanism of soil reinforcement by roots.

This paper presents a novel micropolar-based hypoplastic model to reproduce the stress-strain relationship of face mask chips-sand mixtures (MSMs) and their localized deformation. Based on a critical state hypoplastic model, a non-polar hypoplastic model for MSMs is first developed with modifications and new features: (1) the cohesion induced by face mask chips is considered by introducing an additional stress tensor into the Cauchy stress tensor; (2) the initial stiffness variation in MSMs is described with a modified tangential modulus; and (3) the effective skeleton void ratio concept is introduced to capture the initial and critical void ratio variations in MSMs. The model is then extended to its micropolar terms by incorporating the micropolar theory, which includes an internal length parameter and a couple stress induced by particle rotation, with the advantage of overcoming the mesh dependency problem in the conventional finite element method (FEM) based simulations. Moreover, the new micropolar hypoplastic formulations are implemented into a FEM code. The onset and evolution of shear bands in MSMs are investigated by simulating a series of biaxial tests on both pure sand and MSMs. Numerical results are also compared to experimental observations, demonstrating that the developed micropolar hypoplastic model can adeptly capture the shear band propagation in MSMs and their mechanical responses.

To determine the effects of root volume density on the mechanical behaviour of sand, drained and undrained triaxial compression tests were conducted on sand with root volume densities of 0.8%, 1.2%, 1.6%, 2.0%, and 2.4% under different confining pressures. Higher root content formed a denser and more uniform root network in the soil, enabling more roots to mobilize tensile stress, share external loads, and limit volumetric deformation. This enhanced the root-soil composite strength, reduced volumetric strain under drained conditions, and decreased excess pore water pressure under undrained conditions. The roots made a more pronounced contribution to the soil shear strength under lower confining pressures and undrained conditions. Specifically, with increasing confining pressure, the increment in the inherent soil strength far exceeded that in the additional strength provided by the roots. Under undrained conditions, the roots enhanced the soil strength by bearing part of the external loads and preventing the development of excess pore water pressure. Furthermore, the critical state line of a root-soil composite depended on the stress path. Since roots are non-granular materials and their mechanical reinforcement effect varies under different stress paths. Additionally, the roots enhanced liquefaction resistance of the sand by raising the initial effective stress required for triggering static liquefaction and the critical state effective stress. The greater the root volume density was, the stronger the liquefaction resistance of the sand.

This study investigates the mechanical response and performance of biaxial polypropylene geogrid specimens cyclic loading. This work assesses the influence of embedment depths and subgrade strengths on the of geogrids. The experimental program involved subjecting the geogrid specimens to 100 repeated tensile loading cycles at four distinct load targets: 20%, 40%, 60%, and 80% of the geogrid ultimate tensile strength. The analysis focused evaluating the effects of preloading factors such as California Bearing Ratio (CBR) values, embedment depth, and the response to cyclic testing. Results show trends in stiffness reduction and changes in damping ratio with increased number of cycles. A comparative analysis was conducted with a control specimen from the same batch, highlighting the difference in mechanical response attributed to precycling variables. The findings indicate that the overall mechanical behavior of recovered geogrids is comparably consistent with new geogrids. However, variations in strain and stiffness reduction were observed among the recovered specimens, suggesting a pattern of yielding before failure. The findings suggest a minimal effect of embedment depth on the damping ratio at lower CBR. Overall, it was found that precycling and subgrade conditions have minimal effect on the mechanical response of the recovered specimens when tested in isolation.

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.

Soil reinforcement remains a vital task of a geotechnical engineer. There are a few support strategies for counting sands considered in this field that are strengthened by combined hydraulic binder (such as cement) and/or fibres. The behaviour of such mixtures (sand-cement and sand-cement-fibre mixtures) in terms of direct shear response has been subject to a lot of controversy in the literature. The base material used in the framework of this study is Chlef sand (taken from Chlef Valley, Algeria), mixed with cement and reinforced with synthetic fibres and considering the use of a direct shear device. , mixed with cement and reinforced with synthetic fibres. The types of fibres in terms of the materials used in the manufacture as well as their length and physical characteristics can improve the stress/strain response of sands. Laboratory results show that the shear strength response of sand-cement mixture increases the shear strength of this last and that it was observed with the addition of cement to the sand. The tests done on the mixtures of sand and cement and on fibre-reinforced mixtures showed better strength compared with just sand or cemented sand alone. Adding fibre to the mixture improved the soil's ability to withstand shear forces. As the threshold value, the fibre content should be at least 0.15% in order to make a noticeable improvement in the mechanical properties. This increase in shear strength is noticed accompanied by a limitation in the samples' contractiveness.

The paper explores challenges arising from the existence of expansive clay soils, renowned for causing structural damage and exhibiting detrimental environmental effects. Implementing a novel approach, this study introduces the use of fly ash (Class F) and shredded face masks (FMs) to enhance soil properties. Fly ash (FA), known for its pozzolanic properties, is combined with shredded waste FMs to reinforce the soil. Remolded specimens underwent comprehensive laboratory testing, including Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), Swell Test, Consolidation Test, and Triaxial Test. The optimal blend identified as 0.9% FMs + 20% FA achieves an optimal equilibrium of strength, stability, and reduction in swelling. The UCS exhibited an increase with the addition of FA, and this improvement was further enhanced with the inclusion of 0.9% FMs, surpassing the specified subgrade CBR values. The percentage of swell exhibited a notable decrease from 5.9% to 1.8% with the incorporation of FA + FMs. This sustainable approach aims to conserve valuable resources and mitigate challenges associated with waste disposal along with the economic benefits to contribute to achieve UN SDGs 2030.

Sandy soils are a type of geomaterial that may require improvements due to lack of cohesion. In this study, first, the lack of cohesion of sand was resolved using clay, and the soil was stabilized with cement and lime (4% and 3% of the dry weight of materials, respectively) and finally reinforced with recycled tire fibers of 20 to 30 mm in length for improved strength and ductility. Next, 747 samples with different fiber contents at different curing temperatures and ages were prepared and a unconfined compressive strength (UCS) test was carried out. Next, a novel approach employing multivariate nonlinear regression techniques and obtained empirical data was applied to formulate a mathematical model for predicting the UCS and the modulus of elasticity (E-s) of the reinforced and stabilized soil. This model can serve as a valuable tool for building engineers in designing building foundations. The comparison of the obtained UCS and E-s results and those predicted using the proposed model showed a correlation of >95% (R-2 >= 0.95). The fibers effectively increased the failure strain, thus resulting in the greater ductility of the samples. As an example, in 14-day samples cured at 60 degrees C with 0%, 0.4%, 1%, 1.7%, and 2.5% fibers, the failure strain showed an incremental trend of 1.47%, 1.87%, 2.08%, 2.20%, and 2.92%, respectively. Scanning electron microscopy (SEM) was used to study the microstructure of the samples and to explain the strength experimental outcomes. SEM images showed a desirable interaction between the fiber surfaces with the soil mass and the reduction in porosity and the occurrence of pozzolanic reactions through stabilization. The results also showed that the reinforcement effectively improved the ductility, as desired for building foundations; however, it resulted in reduced strength, although a greater strength compared to the untreated soil was achieved. Although soil stabilization has been widely studied, limited research focuses on stabilizing soil with clay, lime, cement, and recycled tire fibers. This study offers design engineers an estimation scheme of the strength properties of stabilized and reinforced foundations.

The changing climate raised more concerns about the durability of aged slopes and embankments due to the increased frequency of extreme rainfall events. Recently, there has been a growing interest in the utilization of biopolymer as a biomediated soil improvement method. However, challenges, such as, strength loss due to exposure to adverse environmental conditions and limitations on the suitability of soils for effective treatment, can be problematic in practice. Therefore, this study introduces an innovative approach by combining biopolymer with another eco-friendly material, biochar. The erodibility of the reinforced soil was examined through both wetting and drying tests and slope-rainfall simulation tests with the consideration of different rainfall intensities and slope inclinations. The findings suggest that cyclic wetting and drying conditions can lead to a progressive degradation (decrease in strength) of soils reinforced with biopolymer, starting from the initial cycle. Conversely, incorporating biochar into the biopolymer-reinforced soils successfully postponed this decline in both compressive and shear strength, prolonging the soil's resilience by two to three cycles. In addition, soil slopes reinforced with the combined treatment exhibited reduced soil runoff and increased durability under both light and heavy rainfall compared to slopes reinforced with either biopolymer or biochar alone. The findings of this study provide an innovative method for controlling soil erosion on sandy soil, suggesting its potential application in slope stabilization and restoration.

Millions of tonnes of bagasse are annually generated as waste from the sugar industry, the disposal of which poses a critical global challenge. To address this, the study explores the potential utilization of sugarcane bagasse fibers as a reinforcing material to sand, aiming to enhance its mechanical properties through laboratory investigations. Initially, the primary physical characteristics of both sand and bagasse fibers are examined using laboratory tests and scanning electron microscopy. Further, consolidated drained triaxial compression tests were carried out on sand specimens, with fiber contents varying from 0 to 2%. The investigations encompass the influence of fiber content, fiber length, and effective confining pressures on the strength parameters, dilation, and stiffness of reinforced sand. Upon shearing, the bagasse reinforced sands exhibited a strain-softening behavior at low fiber contents and a strain hardening behavior at higher fiber contents. Results indicate the beneficial utilization of bagasse fiber in enhancing the strength parameters, and reducing the residual strength loss of sand, sensitive to the effective confining stress. With increase in percentage of bagasse fiber, the dilation of sand was found to be decreasing. The inclusion of bagasse fibers also leads to a reduction in the initial and secant stiffness of the sand. Furthermore, as the length of fiber shortens at same percentage of fiber, the peak and critical angle of friction reduces. Based on the test results, a normalized model of the reinforced sand has been developed to capture the peak and residual states of the sand in correlation with different critical parameters.