Effect of fiber reinforcement on shear strength and void ratio of soft clay

In this study, a series of multi-stage drained reverse direct shear tests were carried out on soft clay samples reinforced with 0.25% and 0.50% polypropylene fibers of 6 mm, 10 mm and 19 mm in length. Tests were carried out at different normal effective stresses and cumulative horizontal shear displacement of 1.17 times of the sample width. Results showed an increase of the shear strength with the increase of fiber content and length. However, the rate of improvement was capped with the normal effective stress applied during the shearing stage. At a high normal effective stress, the shear strength of the fiber-reinforced soft clay approached that of the unreinforced clay regardless of the amount of fiber inclusion. The rate of shear strength improvement decayed with the number of shear cycles. Fiber reinforcement also resulted in a reduction of the compressibility of the soft clay at consecutive consolidation and shear stages. Although the effective internal friction angle of the soft clay was not altered significantly with the fiber reinforcement, the effective cohesion of the soft clay improved significantly as much as 6.4 and 8.5 times with the inclusion of 0.25% and 0.50% of 10 mm long fibers, respectively.