Abstract:With the development of national economy

a large number of engineering projects were constructed in cold regions.Studying the mechanical properties of frozen soils is of great importance for engineering construction in cold regions.During the numerical analysis of coupled water

heat and stress in saturated freezing soil

it is necessary to construct a frost heave model reflecting moisture migration and the formation process of segregated ice lenses.Considering the influence on the driving force of water caused by suctions on the ice water interface and relations between the coefficient of transmissivity and void ratio in unfrozen soil zone

expressions of hydraulic head and hydraulic conductivity were modified on the basis of existing coupled model.Our results showed that the pore structures of the modified models appeared different degree of change

causing differences in the formation and distribution of ice lenses.After the expression of hydraulic head was modified

the frost heave curve of model behaved as an “S” type

the thickness of ice lenses increased and the time when ice lenses appeared advanced.Due to a decreasing permeability coefficient with the reduction of void ratio in unfrozen soils

the amount of moisture migration and frost heave was greatly reduced

and the time when ice lenses appeared was delayed.Based on the simulation results

the formation and stratification of ice lenses was theoretically analyzed.Ice lenses could be formed if there was sufficient water migrated to frozen soil zone before the formation of an aquiclude.The stratification of ice lenses depended on the capability of ice crystals separating soils and forming ice lenses.Combined with the Darcy’s law

the hydrating rate was used to reflect the influence of both hydraulic head and hydraulic conductivity on our results.The existing separation criterion could be used to explain the growth of final segregated ice lenses and it is suggested that the hydrating rate shoud be the criterion for the formation of early ice lenses.