Experimental study on the triaxial unloading creep characteristics of stone with two pre-existing cracks and its damage creep model

In order to understand the unloading creep characteristics of fractured rock,the sandstone specimens with two pre-existing cracks were prepared,then the unloading creep test with the axial pressure remaining stationary and the lateral stress unloading gradually was performed in laboratory. The results show that for the deviator stress at fail- ure,the minimum value was found for low-low angle type specimen and high-low angle type specimen,followed by high-high angle type specimen and intact sandstone. Under the same stress level,the maximum value of instantaneous strain and creep strain were found for low-low angle type specimen,followed by high-low angle type specimen,high- high angle type specimen and intact sandstone. The traditional element models were presented for the creep curves of all specimens,the results show that the intact specimens and fractured specimens have the same form of constitutive model,just the parameters are different. Based on the research results,the fractured rock mass damage creep constitutive models were put forward by using the equivalent strain and energy equivalent principle,and then compared with the laboratory tests results. The relationship between the intact rock and fractured rock mass was established by these fractured rock mass damage creep constitutive models.