Experimental Study on Unconsolidated Undrained Shear Strength Characteristics of Synthetic Cotton Fiber Reinforced Soil

To research the unconsolidated undrained shear strength and deformation properties of saturated cotton fiber reinforced soil, the shear strength of saturated fiber reinforced soil is studied through a series of unconsolidated undrained shear tests. The test results show that the stress–strain relationship of the fiber reinforced soil is strain hardening, and the failure mode of the samples is bulging failure. Tensile properties of fibers require a certain strain to be “mobilized”. When the strain is less, the fiber content and the fiber length have less influence on the principal stress difference, and the reinforcement effect is weak. The reinforcement effect enhances with the increasing of axial strain. The unconsolidated undrained shear strength of saturated fiber reinforced soil increases first and then decreases with the increasing of fiber content and fiber length. The strength is the best under the condition of 1.0% fiber content and 3.09 cm fiber length, and the strength of fiber reinforced soil increases by 63.5% compared with that of unreinforced soil. Fiber reinforcement can weaken the end effect of the samples, and effectively constrain the radial deformation of the soil. By analyzing the interaction modes between the fibers and the soil particles, it is found that the interaction modes are contact, bending and interweaving. These three actions provide the interfacial shear stress between the fibers and the soil particles, and the tensile stress of fibers to restrict the movement of soil particles, and the interactions improve the shear strength of soil.