Experimental study on the synergistic effect of coir fiber and lime to improve soil performance

To solve the problems of poor engineering properties of clay and low utilisation of coir fiber, a green and high-performance soil was obtained by using coir fiber in synergy with lime for clay reinforcement. Compaction test and unconfined compression test were carried out to analyze the influence of fiber content and lime content on the early compressive strength, axial compression deformation characteristics, and deformation modulus parameters of clay. The microscopic mechanism of the synergistic effect of fiber-lime soil was analyzed by scanning electron microscope and X-ray diffraction, and then the synergistic mechanism was discussed. The results show that the addition of lime reduces the maximum dry density and increases the optimum moisture content of the clay. With an increase in lime content, the compressive strength of the soil initially exhibits a rise followed by a decline. The strain of the soil failure shows a decrease first and then an increase, indicating a brittle failure mode. Similarly, as the fiber content increases, the compressive strength of the soil also experiences an initial increase followed by a subsequent decrease. However, in this case, there is a gradual increase in failure strain suggesting a plastic failure mode. The relationship between deformation modulus and compressive strength of improved soil is linear. Lime fills up pores by reacting with the soil to form gelled substances, while fibers form a three-dimensional network structure providing growth areas for hydration products, thereby synergistically reinforcing the soil. This study can provide theoretical and technical guidance for roadbed improvement and slope repair.