Study on shear performance of cotton straw fiber reinforced mud soil under freeze-thaw cycle

Abstract

To explore the shear properties in cotton straw fiber-reinforced mud soil under freeze-thaw(F-T) cycles, direct shear tests are carried out on soil samples after different F-T times to obtain the influence of fiber content and F-T times to the shear strength of cotton straw fiber-reinforced soil. Then combined with scanning electron microscopy(SEM) to observe the microstructure of fiber and reinforced soil. Results indicate that the shear strength and cohesion of mud soil can be significantly improved by the addition of cotton straw fibers compared with plain soil, and the shear strength and cohesion of reinforced soil are higher than the plain soil during the same F-T times. Among three fiber contents of 0%, 0.2% and 0.4%, the shear strength and cohesion of 0.2% fiber-reinforced soil are higher than those of plain soil and 0.4% reinforced soil. After F-T cycles, the cohesion of soil decreases, among which the decrease is larger for 1 and 3 F-T times, and then the decrease of cohesion will be slowed down gradually, and when the number of F-T times reaches 10, the cohesion becomes stable. The internal friction angle for reinforced soil is higher than the plain soil, and it decreases first, then rises and finally decreases under the effect of F-T cycles, but in general, the changes are not large. The SEM observation shows that the microscopic morphological changes of the fibers themselves are small under the influence of F-T cycles, but the reinforced soil structure is destroyed, the pores and cracks become more, by which the connection between the fibers and soil particles decreases, resulting in a decline in the soil’s shear strength.