Performance of clay soil reinforced with fibers subjected to freeze-thaw cycles

In order to study the strength properties of the weak soil reinforced by fibers, a series of unconsolidated undrained triaxial compression tests of fine-grained soil subjected to freeze-thaw cycles were conducted. Experimental samples were made by adding various contents of basalt and polypropylene fibers (0, 0.25, 0.5, 0.75% of the dry weight of the soil) into clay soil; freeze-thaw cycles were performed in a closed system (0, 2, 5, 8, 10, 15 cycles). Reinforcing fibers of circular cross-section were employed. A decrease in the strength of the test samples was observed with an increase in the freeze-thaw cycle, by carrying out triaxial compression experiments. A comparison of the strength properties of clay soil between unreinforced samples and reinforced ones with different fibers was made. The greatest decrease in the strength of clay was observed in samples after 15 freeze-thaw cycles, but it was noted that the using of fibers helps to prevent a decrease in the strength of clay subjected to the freeze-thaw cycle. After 15 freeze-thaw cycles, the strength of all unreinforced and fiber-reinforced samples decreases approximately by 30-35%. When reinforcing 0.75% with polypropylene fibers, the strength increases by 70%. Inclusion of 0.75% basalt fiber increases the strength by 41.2% before freezing and by 27.1% after the 15th cycle. Cohesion of unreinforced soil after the 15th cycle is reduced from 56.9% of unreinforced soil to 50.4% with reinforcement 0.25%, up to 54.4% at 0.5% and up to 54.0% with reinforcement 0.75% basalt fiber. The resilient modulus of all samples decreases with increasing freeze-thaw cycles, however, samples which were reinforced with fiber showed an increase in the resilient modulus as compared with not reinforced samples both before and after freezing-thawing.