Abstract: In order to further study the interaction mechanism between the fiber and the soil in the fiber reinforced red clay samples and to improve the tensile strength of the soil, this paper presents an investigation result of Guilin red clay using the soil tensile strength testing device and microscope, the tensile tests of different polypropylene fiber content under the maximum dry density and optimal moisture contents. The microscopic mechanism was observed. The experimental results show that the content of the polypropylene fiber can greatly improve the tensile strength and the strain of the red clay, and make red clay sustain a greater tensile deformation. With the increase of the polypropylene fiber content, the tensile strength increases obviously, and the failure type of the red clay changes from the brittle failure mode to the plastic failure mode. Compared with the plain soil samples, the polypropylene fiber content makes the soil appear obvious inflection point when it is failed under the loading. The ultimate tensile strain of the red clay samples increases by 329.9% with the increase of the fiber content. After analysis, the tensile behavior of the fiber improved red clay samples is mainly attributed to the mechanical adhesion force between the soil particles and fibers, which friction each other to resist the fracture. As well as the fiber and fiber interweave to form a fiber network, which is acted by the threedimensional multidirectional tendons to improve the tensile strength of soil samples.

Key words: Polypropylene Fiber, Remolded Clay, Plastic Failure, Tensile Strength, Mechanical Adhesion Force