Effect of repeated freeze-thaw cycles on the resilient modulus for fine-grained subgrade soils with low plasticity index

The resilient modulus of the subgrade is an important material parameter for pavement design. This paper presents an unconfined laboratory testing method for resilient modulus under repeated freeze-thaw cycles. The method was validated by a standard testing method. Specimens of three types of fine-grained subgrade soil with a low plasticity index with five different levels of moisture were tested by the proposed testing procedure. The size of the specimen was 50 mm in diameter and 50 mm in height to more accurately illustrate the freeze-thaw conditions. The numbers of freeze-thaw cycles were designated 0, 3, 6, 9 and 12. The results indicate that all the soils exhibited a substantially reduced resilient modulus after the first three freeze-thaw cycles. After six freeze-thaw cycles, the decrease in the resilient modulus was not obvious. The resilient modulus due to six cycles was suggested for use in pavement design. The reduction coefficients for the freeze-thaw effect were also recommended. These reduction coefficients are 0.5-0.6 for specimens with optimum moisture content and 0.7-0.8 for specimens under dry conditions.