Clay soil tends to crack during desiccation due to soil shrinkage. The existence of cracks in the soil significantly affects the performance of clay soils in various geoengineering applications some examples of such applications include compacted clay barriers in waste containment, pond liners for the storage of liquid wastes, dam cores, and road pavements. Leakage of leachate into the surrounding soils and groundwater and reduced road life cycle are among the threats posed by cracking of clay soils. Thus, cracks propagation in soil is of paramount importance. In this study, it is tried to control clay shrinkage cracks using auxetic yarns. Materials with a negative Poisson ratio are known as auxetic materials. These materials in contrast to conventional materials expand transversally when stretched axially or vice versa. The auxetic materials possess unique properties such as enhanced shear resistance, indentation resistance, fracture toughness, and enhanced energy absorption. In this study, auxetic yarns with optimal characteristics were produced. The Poisson ratio of the auxetic yarn samples at different strain values was calculated. In order to establish the effect of auxetic structure on the control of clay crack propagation, three samples of unreinforced clay, clay reinforced with auxetic yarns, and clay reinforced with auxetic yarn components were prepared. Propagation of cracks in these samples was measured and the results were compared with each other. It was found that the inclusion of auxetic yarns in general results in a 10% reduction of crack propagation in the clay soil. In order to be assured of the positive effect of auxetic yarns on the performance of the clay samples, pullout test was carried out on the samples. It was found that the inclusion of auxetic yarn, very effectively enhances the interaction of the soil and the auxetic yarn. This was attributed not only to the transverse expansion of auxetic yarn but also the indentation feature that occurs in such yarn during pullout. The auxetic feature of the yarn results in 27.3% increase in the force necessary to pull the yarn from the soil matrix. Also, due to the effect of soil pH on the durability and efficiency of auxetic yarns in the soil, the soil pH and the strength of yarns in this environment were eva‎luated. The results showed that the auxetic yarns could withstand the poor alkaline soil environment.

محمد ذره بيني، مهدي ابطحي

محسن شنبه

مهدي حجازي، هاجر شرع اصفهاني