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In this study, the numerical direct shear tests were conducted to investigate the shear mechanical properties of joint networks under constant normal stiffness (CNS) boundary conditions. The influence of random joint number on shear stress (τ), dilation (normal displacement, δv) and normal stress (σn) of rock mass were studied quantitatively with fixed main slip surface. At the same time, the internal stress evolution process and failure process were analyzed. The results reveal that the number of random joints (γ) has little effect on the shear and normal stresses. The normal displacement of the sample generally decreases as the number of random joints increases. In addition, the normal displacement of the specimen is absorbed by the random joints when the number of random joints in the specimen increases to a certain level: when γ is greater than 6 and the shear displacement (μ) reaching 10 mm, the specimen exhibits shear contraction. Therefore, the internal random joints mainly control the failure mode and dilatancy performance of the specimen, while the main joint of the rock controls the shear stress of the specimen.

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Fiber-reinforced concrete (FRC) has apparent benefits over traditional cementitious composites and possesses a great prospect in civil engineering projects. Previous studies reported that fiber admixtures could effectively enhance the mechanical properties, impermeability, and durability of cementitious composites. Nevertheless, the trade-off of the reinforcing efficiency, cost, and properties of the cementitious composites in different aspects has been a challenge in the application of FRC to practical engineering. This article summarizes a review concerning the recent development of FRC enhanced by different fibers and mainly focused on the fiber-reinforcing effects on the microstructure and the corresponding properties of cementitious composites. The addition of a small amount of fiber material has a significant change in the microstructure and related properties of cement-based materials, but the presence of fibers also causes structural damage and other problems. The direction of future development of some cutting-edge technologies such as coating and hybridization methods on fiber modification was concluded to assist further research in FRC. This review will further enhance the understanding of fiber for reinforcing cementitious composites.