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 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.

Modeling approaches to fully capture the behavior of fiber-reinforced clay remain lacking, although the beneficial role of discrete short fibers in reinforcing soils is an established concept. This lack results from tremendous difficulties in characterizing the complex interaction mechanism between fiber and soils. Based on a thorough analysis of the interaction mechanism in terms of stress and deformation pattern, this paper developed a modeling approach to predict the before-failure and failure behaviors of fiber-reinforced clay subjected to triaxial compression. The approach was built on the innovative combination of the superposition method with the energy-based homogenization technique by using two reasonable assumptions about the interaction mechanism: (1) the active fibers work in their elastic domains throughout the entire loading process; and (2) the active fibers’ partial slippage along the interactive course controls the composite’s before-failure behavior, whereas the failure of the composite is governed by fiber pullout. The before-failure behavior was modeled by establishing an elastoplastic stiffness matrix derived from superimposing the incremental stress contributions of the fiber phase and the clay phase described by the modified Cam-clay (MCC) model that is capable of reflecting the nonlinearity. A macroscopic failure criterion that can be used as an alert for the attainment of the failure state was developed based on the equilibrium of the rates of work dissipated on the interactive course and in the clay matrix. Good agreement of the predicted behavior with the observed response in drained triaxial compression tests verified the approach’s ability in accurately reproducing the stress–strain and volumetric behavior of fiber-reinforced clay despite some discrepancies between the predicted and experimental results. The discrepancies direct the further refinement of the proposed modeling approach, which is expected to serve as an effective tool that can be used for deformation and stability analysis of fiber-reinforced geotechnical structures.