Large Scale Direct Shear Experiments to Study Monotonic and Cyclic Behavior of Sand Treated By Polyethylene Terephthalate Strips

The continuously increasing production of plastics in the last few decades has taken a heavy toll on the environment. Soil reinforcement with the use of randomly distributed fibers, plastics and glass has recently received a lot of attention. The use of polyethylene terephthalate (PET) strips as soil reinforcement has been observed to result in the increase in the shear strength. In this paper, the monotonic, cyclic, and post-cyclic properties of sand reinforced with different contents and aspect ratios of PET strips are investigated by carrying out a set of monotonic and cyclic direct shear tests. Accordingly, the influence of various parameters on the direct shear response of sand-PET mixture is examined. Results show that in the monotonic tests, for mixtures containing 0%, 0.5%, 0.75% and 1% PET with A(R) = 1, the peak friction angle is 37.5 degrees, 41.8 degrees, 42.7 degrees, and 44.6 degrees, repectively, while these values increase to 41.8 degrees, 45.4 degrees, 48.2 degrees, and 50.4 degrees, respectively, for post-cyclic monotonic tests. In addition, in the monotonic tests, for mixtures containing 0.5%, 0.75% and 1% PET with A(R) = 5, the peak friction angle is 48.8 degrees, 52.2 degrees, 54.0 degrees, respectively, while these values increase to 50.9 degrees, 54.8 degrees, 55.9 degrees, respectively, for post-cyclic monotonic tests. Results clearly imply that normal stress and cyclic shear strain amplitude contribute jointly to the contractive behavior of the reinforced mixtures. Moreover, the hardening behavior becomes less eminent when the sand is reinforced with PET strips due to the resistance mobilized against particle rearrangement. The post-cyclic shear strength of the PET-sand mixture is higher than their monotonic strength due to the densification occurring during the cyclic loading. In summary, the favorable impact of PET inclusion on the monotonic and cyclic performance of granular materials is deduced.