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.

In this study, lime soil was reinforced with preservative-treated rice straw fibers to improve its brittle behavior and overall performance. Straw fibers of varying lengths and amounts were used, and the resulting unconfined compressive strength, shear strength, and flexural strength of the reinforced soil were determined. The effect of fiber reinforcement on the mechanical properties and fracture toughness of limestone soils was determined, and the finite element (FE) software ABAQUS was used to analyze the specimen loading, crack extension, and specimen damage for developing a fracture toughness prediction model. The test results showed that the compressive strength, shear strength, and Mode I fracture toughness of soil increased with the fiber length and content. Also, a linear correlation between fracture toughness and unconfined compressive strength and shear strength was found. Therefore, the fracture toughness can be predicted by establishing a correlation equation. The disparity between the simulated fracture toughness obtained by FE analysis and that measured laboratory test is <3 %, validating the reliability and accuracy of the developed model. From the FE model analysis, crack propagation can be divided into four stages, i.e., no crack, crack appearance, crack development and expansion, and crack penetration. The friction and interlocking force between the rough texture of the fiber surface and the soil and the skeleton structure formed by the fiber in the soil can overcome the soil force. Therefore, the toughness of fiber-reinforced soil is better than that of lime soil.

This study shows the influence of the inclusion of abaca fiber (Musa Textilis) on the coefficients of consolidation, expansion, and compression for normally consolidated clayey silt organic soil specimens using reconstituted samples. For this purpose, abaca fiber was added according to the dry mass of the soil, in lengths (5, 10, and 15 mm) and concentrations (0.5, 1.0, and 1.5%) subjected to a curing process with sodium hydroxide (NaOH). The virgin and fiber-added soil samples were reconstituted as slurry, and one-dimensional consolidation tests were performed in accordance with ASTM D2435. The results showed a reduction in void ratio (compared to the soil without fiber) and an increase in the coefficient of consolidation (Cv) as a function of fiber concentration and length, with values corresponding to 1.5% and 15 mm increasing from 75.16 to 144.51 cm2/s. Although no significant values were obtained for the compression and expansion coefficients, it was assumed that the soil maintained its compressibility. The statistical analysis employed hierarchical linear models to assess the significance of the effects of incorporating fibers of varying lengths and percentages on the coefficients, comparing them with the control samples. Concurrently, mixed linear models were utilized to evaluate the influence of the methods for obtaining the Cv, revealing that Taylor's method yielded more conservative values, whereas the Casagrande method produced higher values.

Large volumes of waste tires are generated due to the rapid growth of the transportation industry. An effective method of recycling waste tires is needed. Using rubber from tires to improve problematic soils has become a research topic. In this paper, the dynamic response of rubber fiber-reinforced expansive soil under freeze-thaw cycles is investigated. Dynamic triaxial tests were carried out on rubber fiber-reinforced expansive soil subjected to freeze-thaw cycles. The results showed that with the increase in the number of freeze-thaw cycles, the dynamic stress amplitude and dynamic elastic modulus of rubber fiber-reinforced expansive soils first decrease and then increase, and the damping ratio first increases and then decreases, all of which reach the turning point at the 6th freeze-thaw cycle. The dynamic stress amplitude and dynamic elastic modulus decreased by 59.4% and 52.2%, respectively, while the damping ratio increased by 99.8% at the 6th freeze-thaw cycle. The linear visco-elastic model was employed to describe the hysteretic curve of rubber fiber-reinforced expansive soil. The elastic modulus of the linear elastic element and the viscosity coefficient of the linear viscous element first decrease and then increase with the increase in the number of freeze-thaw cycles; all reach the minimum value at the 6th freeze-thaw cycle. The dynamic stress-dynamic strain curve calculation method is established based on the hyperbolic model and linear visco-elastic model, and the verification shows that the effect is better. The research findings provide guidance for the improvement of expansive soil in seasonally frozen regions.

Geomechanics tests and theories have confirmed that soil exhibits noncoaxial behavior under the rotation of principal stress. A series of hollow torsional shear tests were conducted in this study on fiber-reinforced soil using a hollow cylinder apparatus (GDS-SSHCA). Factors including deviatoric stress, q, the coefficient of intermediate principal stress, b, and fiber content, FC, potentially influencing the shear strain, volumetric strain, and noncoaxiality of fiber-reinforced aeolian soil were evaluated in the tests. The results revealed that both shear and volumetric strains of the fiber-reinforced aeolian soil samples increased as deviatoric stress and the coefficient of intermediate principal stress increased. However, the impact of fiber content initially decreased and then increased. Maximum shear strain and volume strain values were measured at 0.44% and 0.517%, respectively, with an optimum soil content of 3 parts per thousand. During pure principal stress axis rotation, the fiber-reinforced aeolian soil exhibited noncoaxial characteristics and a fluctuating noncoaxial angle. The average noncoaxial angle decreased to a minimum of 23.59 degrees as the deviatoric stress, the coefficient of intermediate principal stress, and the fiber content increased. Based on the range-analysis method, deviatoric stress was found to have the most pronounced effect on the average noncoaxial angle, followed by the coefficient of the intermediate principal stress and the fiber content. A shear strain prediction equation considering noncoaxiality under pure principal stress axis rotation was established and verified against previously published data. The equation's accuracy was further confirmed through comparison with monitoring data. These findings may serve as a valuable theoretical reference for preventing geological engineering disasters.

Mixed fiber reinforced technique has been widely used in reinforcing the concrete due to its excellent performance in enhancing the strength, durability and stiffness. The improvement of fiber-reinforced soil (FRS) on the mechanical behaviour (e.g., stiffness and ductility) is limited due to the properties of single fibers. However, much studies focus on the single fiber based reinforced soil, two fibers or more mixing with soil do not be covered. Mixed fiber-reinforced soil (MFRS) is defined as the improvement of FRS, in which two different types of fibers are mixed into the soil to improve the shear strength and stiffness simultaneously. The tests were conducted using clay soil and Yongjiang sand, which were collected from the practical construction site of metro and Yongjiang River, respectively. The test results show that under the same test conditions (e.g., void ratio, confining pressure and fiber content), the MFRS always show higher deviator stress than the FRS. As carbon fibers and polypropylene fibers give higher stiffness and tensile strength respectively. Besides, the friction angle and cohesion of MFRS are also affected by fiber content. It is concluded that half of the carbon fiber content of MFRS has the same performance in the stress-strain relationship as the FRS with 100% carbon fiber content. However, the effectiveness of the reinforcement to clay soil is insignificant. As the reinforcements is relatively dependent on the characteristics of clay soil (e.g., mean diameter, coefficient uniformity). For the use of MFRS, it could decrease the cost of purchasing special fiber such as pure carbon fiber and aramid fiber, which are expensive, and it could be used in the long-terms constructions, which are required to last at least 100 years.

With the growth of the transportation industry, large volumes of waste tires are being generated, which necessitates the development of effective solutions for recycling waste tires. In this study, expansive clay was mixed with rubber fibers obtained from waste tires. Triaxial tests were conducted on the rubber fiber-reinforced expansive clay after freeze-thaw cycles. The experimental results of the unreinforced expansive clay from previous studies were used to evaluate the effect of mixing rubber fibers on the mechanical properties of rubber fiber-reinforced expansive clay under freeze-thaw cycles. The results demonstrate that the mixing of rubber fibers significantly reduces the effect of freeze-thaw cycles on the shear strength and elastic modulus of expansive clay. The shear strength and elastic modulus of the unreinforced expansive clay decrease markedly as the number of freeze-thaw cycles increases, while the shear strength and elastic modulus of the rubber fiber-reinforced expansive clay do not exhibit any remarkable change. A calculation model of the deviatoric stress-axial strain curves after freeze-thaw cycles was established. The model describes the deviatoric stress-axial strain behavior of rubber fiber-reinforced expansive clay and unreinforced expansive clay under different confining pressures and different numbers of freeze-thaw cycles.

Adding fibers into cement to form fiber-reinforced soil cement material can effectively enhance its physical and mechanical properties. In order to investigate the effect of fiber type and dosage on the strength of fiber-reinforced soil cement, polypropylene fibers (PPFs), polyvinyl alcohol fibers (PVAFs), and glass fibers (GFs) were blended according to the mass fraction of the mixture of cement and dry soil (0.5%, 1%, 1.5%, and 2%). Unconfined compressive strength tests, split tensile strength tests, scanning electron microscopy (SEM) tests, and mercury intrusion porosimetry (MIP) pore structure analysis tests were conducted. The results indicated that the unconfined compressive strength of the three types of fiber-reinforced soil cement peaked at a fiber dosage of 0.5%, registering 26.72 MPa, 27.49 MPa, and 27.67 MPa, respectively. The split tensile strength of all three fiber-reinforced soil cement variants reached their maximum at a 1.5% fiber dosage, recording 2.29 MPa, 2.34 MPa, and 2.27 MPa, respectively. The predominant pore sizes in all three fiber-reinforced soil cement specimens ranged from 10 nm to 100 nm. Furthermore, analysis from the perspective of energy evolution revealed that a moderate fiber dosage can minimize energy loss. This paper demonstrates that the unconfined compressive strength test, split tensile strength test, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) pore structure analysis offer theoretical underpinnings for the utilization of fiber-reinforced soil cement in helical pile core stiffening and broader engineering applications.

Recycling waste for soil improvement is a cost-effective strategy to mitigate the energy consumption and carbon emission of traditional stabilization materials (cement, lime, etc.). This paper proposes an eco-friendly geotechnical improvement using recycled polyester fiber (RPF) and red mud to synergistically reinforce volcanic ash. For red mud -reinforced volcanic ash (RV) with five different RPF contents, a series of mechanical tests, water stability tests, microstructure tests and environmental impact tests were performed. Results show that RPF can significantly improve the mechanical performance and water stability of RV. The reinforcement increases with increasing RPF content, and the optimum contents of RPF is 0.9%. For specimens with optimum RPF incorporation, Unconfined compressive strength (UCS), splitting tensile strength are increased by 122%, 180%, respectively. It also allows saturated soil to still maintain higher UCS and the soil does not completely disintegrate in submerged environment. The pH value and toxicity leaching indicators of specimens both satisfy the specification limits and therefore the material has no environmental hazard. TGA, FT-IR and SEM-EDS indicate that the reinforcement mechanism of RPF on RV derives mainly from fiber-matrix interactions, including interface bonding, bridging effect and limiting micro-cracks development. RPF reinforced RV presents favorable engineering performance as a sustainable construction material and can contribute to the win-win objective of environmental conservation and waste recycling. This low-carbon and sustainable soil improvement technology can serve and guide the design of geotechnical engineering in volcanic areas.