Experimental Investigation on the Effect of Teff Straw Fiber and Lime on Strength and Compressibility of Black Cotton Soil

Abstract

Black cotton soils often do not meet the geotechnical requirement as they exhibit high swelling-shrinkage behavior and compressibility. Therefore, stabilization of such soils with different additives is a common practice in geotechnical engineering. On the other hand, replacing traditional stabilizers with industrial and agricultural by-products has both economic and environmental significance. In this work, the effect of teff straw fiber, which is one of the common agricultural by-products in Ethiopia, on strength and compressibility characteristics of black cotton soil, was investigated. The combined effect of fiber reinforcement and lime treatment was also investigated. The black cotton soil sample was collected from Sendafa town. Samples of soil reinforced with various contents (0%, 0.5%, 0.75%, and 1% by weight) and lengths (20mm, 40mm, and 60mm) of teff straw fibers and mixed with various percentages of lime (2%, 4%, and 6%) were prepared to conduct compaction test, unconfined compressive strength (UCS) test, and consolidation test. The result showed that maximum dry density (MDD) decreased and optimum moisture content (OMC) increased with increasing both fiber and lime percent, while USC increased until 0.75% for teff straw fiber with each length and 4% (optimum %) of lime. The strength increased by more than double when the soil is reinforced with optimum percentage (0.75%) of fiber content and treated with lime (4%) as compared to when the soil is stabilized by lime (4%) only. Similarly, fiber reinforcement and lime stabilization significantly reduced the compressibility and swelling potential of soil. The finding of the work suggests that a combination of fiber reinforcement and lime stabilization is more effective for ground improvement than lime stabilization or fiber reinforcement alone.