Improvement of the undrained shear strength of silty soil by the addition of basalt fibers

In order to improve the mechanical properties of soils and concrete, an increasing number of different fibers are used. Today, with the environmental problems, the materials used to improve soil and concrete must be environmentally tolerated and ecological. Steels, synthetic fibers and natural fibers are usually used in the field of construction while natural fibers are mostly used in soil improvement. Although basalt originated fibers have been used for concrete for many years, it is not easy to find a source in literature concerning the use of basalt fibers for soil improvement. In this experimental work, unsaturated and saturated samples of soil mixed with basalt fibers were prepared and undrained shear strength of each sample were tested. The sample used in this study was taken between 3 to 4 m deep from Adapazarı city. In the first part of the study, the natural soil samples were compacted at five different water contents. The soil samples were consolidated under vertical stress of 100 kPa - 200 kPa and 300 kPa in the second part of experimental work. After compaction and consolidation, 4 cylindrical samples were taken and the unconsolidated undrained triaxial (UU) tests were performed. Then the same procedure was carried out on the same soil mixed with basalt fibers of different lengths 6 mm - 12 mm and 24 mm at different percentages of 1% - 1,5% and 2% depending on the dry weight of the soil. In order to make a correlation between the microscopic images and the microstructure, the SEM analysis were carried out on the naturel soil samples and those improved with the basalt fibers. The results of 320 UU tests show that the addition of the basalt fibers improved the shear strength of all of the samples regardless of the degree of saturation. As the length of the fibers used increases, the improvement of the sample becomes better. The best shear strength is obtained for the fiber of 24 mm and 1,5% respectively. When the percentage of basalt fiber reaches 2%, the resistance decreases. Compared to the results obtained, basalt fibers can be used as an alternative material to reinforce soil in addition to concrete.