Effects of Freeze-thaw Cycles on the Strength of Straw Fiber-reinforced Soil

Straw fiber-reinforcement is a newly developed soil improvement technology. The variation in soil strength caused by seasonal temperature changes damages the safety and stability of geotechnical engineering projects. To investigate the effects of freeze-thaw cycles on the strength of fiber-reinforced soil, the unconfined compressive tests and the direct shear tests of reinforced samples are carried out after different freeze-thaw cycles. The test results indicates that unconfined compressive strength and the cohesion of the soil samples decreases exponentially with the increasing number of freeze-thaw cycles. However, the decrease ratio of the reinforced soil is smaller than that of the unreinforced soil. The internal friction angle of the soil samples increases exponentially with the increasing number of freeze-thaw cycles. Moreover, SEM indicates that a very distinct increase in the amount of pores and microfissures is found in the unreinforced soil after the cycles. This leads to the decrease of soil strength. The soil surrounding the fiber becomes less dense after freeze-thaw cycles, which indicates the decrease in the interfacial strength of the fiber/soil. However, the complex spatial stress network established by fibers still plays an role in the reinforcement of the fibers, which can improve the stability of frozen soil.