Mechanical properties soil stabilized with nano calcium carbonate and reinforced with carpet waste fibers

One of the geotechnical engineering strategies for dealing with weak soils in a construction site is to alter their mechanical properties with the assistance of soil improvement techniques. The present study examined the effect of the addition of nano calcium carbonate (0, 0.4, 0.8 and 1.2% by weight of the soil) as a stabilizing nanoparticle and carpet waste fibers (0, 0.2, 0.4, and 0.6% by weight of the soil) as a reinforcement agent on the soil behavior. A total of 52 unconfined compressive strength tests, 52 ultrasonic pulse velocity tests, 12 unconsolidated undrained (UU) triaxial tests, and 8 Atterberg limit tests were performed to investigate the effect of fiber and nanoparticle contents and treatment time on the geotechnical properties of the clayey soil. The results showed that the addition of nanoparticles to the clayey soil reduces its liquid limit and increases its plastic limit. The best improvement in the soil strength, which was about 100%, was observed in the 42 days old sample with 1.2% nano calcium carbonate content. The combined use of fibers and nanoparticles also led to significant strength improvement. The addition of carpet waste fiber was found to increase the soil stiffness. Increasing the carpet waste fiber content above the 0.2% did not have much impact on the maximum strength, but significantly improved the residual strength. The addition of carpet waste fibers up to 0.2% increased the velocity of ultrasonic waves, but further increase in the fiber content resulted in reduced velocity. The paper provides a number of equations that express the relationship between the unconfined compressive strength and the ultrasonic pulse velocity for the clayey soils with different additive contents. The provided equations can be used to estimate the success of stabilization and strength improvement efforts based on the results of non-destructive ultrasonic pulse velocity test. The results of unconsolidated undrained triaxial tests showed that the used fibers alter the sample behavior in high strains. Also, the use of nano calcium carbonate and carpet waste fibers together almost doubled the undrained cohesion. (C) 2019 Elsevier Ltd. All rights reserved.