Effects of the Fiber Reinforcement on the Monotonic Behavior of Sands Considering Coupled Volumetric-Shear Strain Paths

Inspired by plant roots, polypropylene fibers can be employed to improve the shear strength of soils. Since the previously applied studies focused on the drained and undrained strength of fiber-reinforced soils (FRS), the dual effects of the different strain paths and fiber contents on the strength properties have been neglected. Recently carried out investigations indicated that strain paths have significant effects on the behavior of soils, where a stable behavior in conventional tests can be changed to a completely unstable behavior. In this paper, the effects of the flexible fibers on the monotonic behavior of sands under different strain paths were investigated for the first time. There is not any previously applied study about the coupled volumetric-shear strain behavior of FRS and this research was aimed to explore such a behavior. Strain paths were conducted by applying controlled volumetric and shear strains, where the ratio between these strains was kept known for the undertaken tests. It is shown that the fiber inclusions can reduce the wrecking effects of strain paths until a threshold value of fiber content, while more fiber contents (more than the threshold value) can reduce their favorable influences. Effects of fiber content on the steady state and phase transformation stress ratios, maximum experienced shear stresses, and generated excess pore pressures were evaluated considering different strain paths, as well.