A large diameter triaxial specimen of 61.9 mm was made by mixing coconut shell fibers with red clay soil. The shear strength of coconut shell fiber-reinforced soil was investigated using a dynamic triaxial shear test with confining pressure in a range of 50-250 kPa, a fiber content of 0.1%-0.5%, and a loading frequency of 0.5-2.5 Hz. The Hardin-Drnevich model based on the coconut shell fiber-reinforced soil was developed by analyzing and processing the experimental data using a linear fitting method, determining the model parameters a and b, and combining the influencing factors of the coconut shell fiber-reinforced soil to improve the Hardin-Drnevich model. The results show a clear distinction between the effects of loading frequency and fiber content on the strength of the specimens, which are around 1 Hz and 0.3%, respectively. Hardin-Drnevich model based on coconut shell fiber-reinforced soil can better predict the dynamic stress-strain relationship of coconut shell fiber-reinforced soil and reflect the dynamic stress-strain curve characteristics of the dynamic stress-strain curve coconut shell fiber-reinforced soil.

Several studies focus on enhancing soil strength through the incorporation of natural or synthetic fibers. However, there is limited published data on the effectiveness of rice husk in soil reinforcement. The use of rice husk as a reinforcing material is supported by the fact that rice is one of the most produced and consumed cereals globally. In this article, we analyze the behavior of a clayey soil from southern Brazil with the addition of 0.5, 0.75, and 1% rice husk (RH), comparing it to coconut coir (CC) and curau & aacute; fibers (CU). In unconfined compressive strength tests (UCS), increases in soil strength of 20, 40, and 140% were observed for RH, CC, and CU, respectively, compared to pure soil. From consolidated undrained triaxial compression tests, both unreinforced soil and soil reinforced with 1% RH, CC, and CU were examined. The triaxial tests revealed an increase in the internal friction angle of 72 and 98%, alongside a decrease in cohesion of 57 and 94% due to the addition of CC and CU, respectively, in terms of effective stress. In contrast, RH did not significantly enhance the soil's behavior, likely due to its shorter fiber length.

An emerging alternative to improve the mechanical properties of fine soils susceptible to cracking is the addition of fibers obtained from reused synthetic materials such as polyethylene terephthalate (PET). The technical literature on the fracture mechanics of PET fiber-reinforced soils is rather scarce, so there has been insufficient progress in determining fracture parameters and standardized procedures to find optimal reinforcement conditions. This research uses experimental techniques to induce tensile stresses in clayey silty soil samples from the Valley of Mexico reinforced with different fiber contents. By applying approaches based on linear elastic and elastoplastic theory, parameters useful for the study of fracture mechanics and flexural strength of PET- reinforced soil were estimated: tensile strength, critical energy release rate, critical stress intensity factor, and contour integral for crack propagation under plasticity. In addition, imaging techniques are used to measure the deformations generated in bending tests of reinforced soil beams and to study crack propagation from initiation to maximum stresses. The addition of PET fibers significantly improved soil response by reducing cracking, increasing tensile strength, and providing ductile behavior as cracking progressed. These effects indicate the great potential of recycled PET fibers as a subgrade improvement method for soft, cracking soil deposits, or even for earthworks and slope stabilization in clayey soils on road projects.

This study explores the mechanical behavior and properties of sand-rubber-gravel (SRG) mixtures under various testing conditions. Through an extensive series of experimental tests-including direct shear, oedometer, saturated and unsaturated triaxial, and cyclic triaxial tests-the effects of rubber and gravel additions on sandy soil are systematically evaluated. The findings reveal that the appropriate content of rubber and gravel is crucial for ensuring the improvement of soil properties. An insufficient addition may not significantly enhance the soil's properties, while an excessive amount can lead to a deterioration of its mechanical characteristics. With the optimal mixture ratio, test results show significant improvements in shear strength and deformation resistance of the SRG mixtures compared to pure sand. Under saturated and unsaturated conditions, the SRG mixtures demonstrate enhanced bearing capacity. In addition, dynamic response of SRG mixtures to varying cyclic loads are revealed through cyclic triaxial tests. The study confirms the feasibility and effectiveness of using SRG mixtures to improve the mechanical properties of sandy soils, suggesting their potential for diverse geotechnical applications.

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.