Stress Path Efforts on Palm Fiber Reinforcement of Clay in Geotechnical Engineering

Abstract

Sixteen Reduced Triaxial Compression (RTC) triaxial tests were conducted to investigate the reinforcement effect of fibered clay in this paper. Palm fiber with four different fiber lengths (5 mm, 10 mm, 15 mm, and 20 mm) and four different fiber contents (0.3%, 0.5%, 0.7%, and 0.9% in mass) were utilized. Accordingly, three additional groups of triaxial tests were performed to analyze the stress path effects with four different stress paths, including RTC, Conventional Triaxial Compression (CTC), Reduced Triaxial Extension (RTE), and isotropic Triaxial Compression (TC). Three samples were tested, including fibered clay with a fiber length of 10 mm and a fiber content of 0.7% (referred to as 10 mm 0.7%), fibered clay with a fiber length of 20 mm and a fiber content of 0.5% (referred to as 20 mm 0.5%), and bare clay, which was used to reveal the fiber reinforcement of clay. All samples were tested under consolidated undrained conditions. The test results showed that in RTC conditions, the deviator stress increased to a greater extent with 0.3% mass content of fibers according to the same higher confining pressures of bare clay. Fibers primarily increased the cohesion of fibered clay, a shear strength parameter, in terms of total stress, whereas they also increased the friction angle of fibered clay in terms of effective stress. For short fibers, the coefficient of strength reinforcement of the fibered clay increased with fiber content. However, for long fibers, this reinforcement may lead to a weakening of the clay’s strength, as the long fibers may cluster or weaken along their longitude. Among the four stress paths (CTC, TC, RTC, and RTE) examined, the reinforcement took effort mainly in the CTC condition. In contrast, in unloading conditions, the fibers had little contribution to reinforcement. Consequently, in unloading conditions, such as deep excavating and slope cutting, the stress path should be considered to obtain a reliable parameter for geotechnical engineering applications.