Concrete-faced-rockfill-dam (CFRD) cannot work properly if the cushion material has too much frost heave deformation. Recent researches have shown that: frost heave deformation of cushion material relates to its pore distribution and gradation. In order to reveal the mechanism of the frost heave of cushion material in cold environment

assumptions are adopted that soil particles are ideal spheres and their distribution is completely uniform

a pore distribution model of cushion material is put forward; and the methods are given for determining the equivalent pore diameter and equivalent pore number. Freeze-thaw cycling tests are carried out on one-way oedometer for different pore sizes and different pore quantities of cushion material. Laboratory frost heave tests results show that the frost heave deformation varies with the size and the quantity of the pore. There exists a critical pore size

when the pore is smaller than the critical size

the smaller the pore and the more the small pores

the greater the frost heave

and vice versa. Based on the proposed pore distribution model

a pore distribution index is defined; it is found to have linear positive correlation between the frost heave deformation of cushion material and this index. The results can be applied for the graduation design of cushion material.