Based on an extensive list of research work, expansive soil is renowned for its swelling-shrinkage property. Despite the wealth of research, the strength characteristics of expansive soil, which are more complicated than common clayey soil and characterized by a considerable loss of postpeak strength, have not been fully investigated. Within this area of study, soil reinforcement with discrete, short natural fibers is attracting increased attention in geotechnical applications, in part thanks to the unique advantages that this material possesses. Because of these possible advantages, the objectives of the study presented in this paper are (1) to investigate strategies for improving the strength characteristics of expansive soil through the introduction of jute fibers into soil mass and (2) to ascertain jute fibers’ reinforcing effects in relation to several important parameters known to control the effectiveness of fiber-reinforced expansive soil. The study presents discussions related to fiber content, fiber length, fiber orientation, water content, and dry density. More specifically, an experimental program of direct shear and triaxial compression tests was performed on unreinforced and reinforced specimens. The results demonstrate the beneficial role of jute fibers in enhancing strength parameters, enhancing deviator stress-strain behavior, and, if the considered parameters are properly selected, in reducing the postpeak strength loss of expansive soil. The study also presents a detailed discussion regarding the variation of the reinforcing effects and regarding the mechanisms accounting for how fiber-reinforcing effects are affected at the fiber and grain scale. Finally, limitations of this study and potential work for the future are contemplated.

The whole shear deformation of rock joints significantly affects the long-term behavior and safety of engineering projects. In this paper, a new damage constitutive model related to the Weibull distribution and statistical damage theory is proposed. This model considers the shear stiffness degradation, post-peak softening, and residual phase of rock joints in the whole shearing process. Main works include the three following aspects: First, the phase of initial damage is determined on the assumption that the joint shear failure is regarded as a result of damage evolution, according to the typical joint shear curve and the three-parameter Weibull distribution. Then, a statistical damage evolution model for the whole joint shearing process is introduced to make this model be capable of describing the residual phase of rock joints. Finally, a statistical constitutive model for the whole joint shearing process is proposed by statistical damage theory, and the calculated results of the models are compared to the experimental results. The results indicate that the proposed model shows a good agreement with the experimental examples, and the proposed model can distinctly reflect the effects of residual stress, peak stress, and shear stiffness. In addition, the model parameters can be mathematically confirmed and have distinct physical meanings.

The beneficial role of combining fiber reinforcement with lime stabilization in altering soil behavior has been established in the literature. However, the coupling effect of their combination still remains unclear in terms of its magnitude and microscopic mechanism, especially for natural fibers with special microstructures. The objective of this study was to investigate the coupling effect of wheat straw fiber reinforcement and lime stabilization on the mechanical behavior of Hefei clayey soil. To achieve this, an experimental program including unconsolidated–undrained (UU) triaxial tests and SEM analysis was implemented. Static compaction test samples were prepared on untreated soil, fiber-reinforced soil, lime-stabilized soil, and lime-stabilized/fiber-reinforced soil at optimum moisture content with determining of the maximum dry density of the untreated soil. The lime was added in three different contents of 2%, 4%, and 6%, and 13 mm long wheat straw fiber slices with a cross section one-quarter that of the intact ones were mixed in at 0.2%, 0.4%, and 0.6% by dry weight of soil. Analysis of the derived results indicated that the addition of a small amount of wheat straw fibers into lime-stabilized soil improved the intensity of the strain-softening behavior associated with mere lime stabilization. The observed evidence that the shear strength increase brought by a combination of 0.4% fiber reinforcement and 4% lime stabilization was smaller than the summation of the shear strength increases brought by their presence alone in a sample demonstrated a coupling effect between fiber reinforcement and lime stabilization. This coupling effect was also detected in the comparisons of the secant modulus and failure pattern between the combined treatment and the individual treatments. These manifestations of the coupling effect were explained by a microscopic mechanism wherein the fiber reinforcing effect was made more effective by the ways in which lime chemically stabilized the soil and lime stabilization development was quickened by the water channels passing through the surfaces and honeycomb pores of the wheat straw fibers.