Contribution of basalt fiber to shear strenght of clayey soils

The increasing population in cosmopolitan cities brought along rapid urbanization, and the necessity of building underground and aboveground structures made the soils valuable. In unfavorable soil conditions, if it is impossible to implement the appropriate location selection and structural change options, soil improvement has been a common method in situations where building construction is necessary. In addition to the functions of soil improvement processes such as increasing the bearing capacity of the soil, reducing the risk of liquefaction, taking control of settlements, increasing the shear strength resistance parameters, it is also emphasized that they are environmentally friendly and economical. Today, in addition to traditional additives such as cement and lime, with increasing technology and knowledge and more technological materials such as fiber, soil improvement has become a part of civil engineering. Basalt fiber is one of the additives used in soil improvement and concrete improvement, which is environmentally friendly, natural, and has a broad raw material base. Soil improvement studies with basalt fiber are increasing in the literature. In this thesis study, the effect of basalt fiber additive on the shear resistance parameters on clayey soils obtained from Düzce province was investigated. Basalt fiber was added to the fine-grained soil samples, which are in the high plasticity clay (CH) class according to the Turkish Standard (TS1500) and the Unified Soil Classification System (USCS), and then subjected to shear box tests. 6 mm, 12 mm and 24 mm long basalt fiber was added to the natural clay sample with a certain weight (0%, 1%, 1.5%, 2%, and 2.5% by weight), and samples were prepared by the slurry method. It was then left to pre-consolidation for 7 days under a 45 kPa load. On the consolidated samples, they were tested with different vertical stresses in the shear box. According to the results, a nonlinear increase was observed in the internal friction angle as the basalt fiber ratio and length ascend. On the other hand, the cohesion value had peaks at different basalt fiber ratios depending on the basalt fiber length. While the cohesion value peaked at the rate of 2% fiber in the samples worked with 6 mm fiber length, the cohesion value peaked at the rate of 1.5% in the samples worked with 12 mm fiber length, and the cohesion value in the samples worked with 24 mm fiber length was 1% fiber. This is explained by the interaction between fiber-soil, fiber length, and fiber ratio (fiber density in the soil sample). It was concluded that basalt fiber could be used as an alternative in soil improvement studies. Keywords: Clayey soil, shear strenght, shear box, soil improvement, basalt fiber.