Single fiber pullout tests on interfacial shear strength of wave-shape fiber-reinforced soils

The interfacial mechanical interaction between fibers and soils is the key factor controlling the engineering properties of fiber-reinforced soils. In order to improve thee mechanical properties of fiber-soil interface, a new wave-shape fiber is developed as a reinforcement material. An innovative pullout test device is designed. By applying this device, a series of single fiber pullout tests are carried out on fiber-reinforced soil samples. The pullout characteristics and interfacial shear strength of wave-shape fiber-reinforced soils are quantitatively obtained. As compared to the conventional straight fibers, the interfacial mechanical interaction character of wave-shape fiber-reinforced soils is analyzed. Moreover, the maximum critical reinforcement length and techniques of wave-shape fibers are discussed. The results show that the proposed single fiber pullout test method and the designed pullout test device are effective to quantify the interfacial mechanical behaviours of the fiber-reinforced soils, with simple operation and good repeatability. The pullout curves of straight fiber present a typical single peak characteristic. As the pullout load reaches the peak value, it decreases rapidly to the residual value, and then gradually reaches stabilization. However, the pullout curves of the wave-shape fibers present a typical characteristic of multiple peaks, and the wavelength of the curve is consistent with that of the wave-shape fibers. It is found that the interfacial shear strength of the wave-shape fiber-soil is significantly higher than that of the conventional straight fiber, and the corresponding strength increases by 178%. It indicates that the wave-shape fibers can dramatically improve the reinforcement benefit as compared with the straight fibers. In addition, the interfacial shear strength and residual shear strength, which are corresponding to the peak values of wave-shape fiber pullout curve, generally decrease exponentially with an increase in pullout displacement. According to the measured fiber-soil interfacial shear strength,