To study the nonlinear fracture mechanical characters of undisturbed frozen soils

the fracture TestⅠand TestⅡ based on the method of undisturbed frozen soils’ field test before have been done. According to the variational rules of heave quantities

the frozen depths and time at different depths

the temperatures were controlled strictly when the specimens were being made and tested. Then the relationship between the specimen displacement of force point and the force has been measured by using the dynamic data acquisition system; and the corresponding nonlinear parameters have been calculated. A new method

which can use nonlinear revision factor to predict fracture toughness of undisturbed frozen soils

has been proposed. Moreover

using present method

nonlinear fracture toughness of TestⅠ and Test Ⅱstraight crack loading and unloading specimens has been also computed. Numerical comparison shows that present results agree well with those computed from rock fracture mechanics. Therefore

this new method could be used to test and revise nonlinear fracture toughness of undisturbed frozen soils.