抄録
In this paper, soil dispersion and structure of particles or aggregates as affected by repetitive freezing— melting processes were examined at a banked slope of a reclaimed field at Abashiri district, Hokkaido. The soil examined was sampled at the volcanic ash subsoil which had a natural structure and almost no history of freezing — melting. The soil was sieved, then packed in plastic containers to an almost homogeneous condition of ρd：1g/cm3 and moisture: a)n. Then freezing—melting cycle was done by freezing the samples at —21℃ for 17h and melting at +27土 5 for 7 h. This is considered as one cycle. After every cycle, dispersion ratio was obtained based on the Middleton method (Dr 1 /50). Also, soil consistency, measuring liquid limit and plastic limit was done in addition to the soft X—ray image method to determine any change in soil structure with increasing number of cycles. Results of the investigations show that dispersion ratio increases up to the earlier cycles, after which an equilibrium condition was attained. It was found that dry strength and shear strength decreased gradually after repetitive freezing — melting. It was understood that the clay activity went down during the earlier cycle of freezing — melting and at later stage, the water holding capacity of soil was also reduced. Soft X —ray images through the image process revealed that soil aggregate structure became weak after repetitive freezing—melting and the volume of coarse pores outside the aggregates increased.
