| The freezing and thawing action in cold zone is a great threat to the long-term stability of many rock mass projects,and due to the anisotropic properties of rock,different mechanical properties are presented.In order to study the crack evolution law and creep mechanical properties of substratum rocks under freezing-thawing process,the T2 spectrum distribution and porosity change of sandstone before and after freezing-thawing cycle were obtained by freezingthawing cycle experiment and nuclear magnetic resonance test.Then the creep test under uniaxial compression was carried out to obtain the creep mechanical parameters of rock.According to the experimental results,the nonlinear creep model of freezing-thawing rock was established and the parameter identification and model verification were carried out.The main research results are as follows:(1)Taking 0 °,22.5 °,45 °,67.5 °,90 ° bedding Angle of sandstone as the research object,to carry out the freeze-thaw cycle test and nuclear magnetic resonance(NMR)test,the results show that with the increase of freeze-thaw cycles,the different Angle of bedding rock porosity and the regularity of T2,embodied in: with the increase of freeze-thaw cycles,the increment of porosity;The pore size changes from small pore to large pore,and new micro pore is formed gradually.The effect of bedding Angle on freezing-thawing is not obvious.(2)Creep tests were carried out with graded loading on rocks with0,30 freezing-thawing times and bedding angles of 0°,22.5°,45° and67.5°,respectively.The test results showed that both freezing-thawing action and bedding Angle had a great influence on the creep process of rocks,as follows: With the increase of bedding Angle,the instantaneous strain in the first stage of loading decreases gradually,while the longterm strength decreases continuously,while the strain in the creep stage of loading under the same stage shows the shape of "increase-decreaseincrease".After freezing-thawing,the strain in the first stage of loading and the creep stage under the same load increases obviously,while its long-term strength decreases.(3)According to the hierarchical load creep test results to elastic modulus is defined considering freeze-thaw damage variable and the Angle of bedding,with defines the creep of rock body strain aging damage variable,and introducing damage factor into the basic rheological device,established the freeze-thaw rock nonlinear creep damage constitutive model and equation,can very good reaction freezethaw layer attenuation and steady creep of rock.In order to reduce the number of parameters and make the model more concise,based on Kachanov theory,an elastic-plastic damage element is introduced.Based on the element model and damage mechanics,the nonlinear creep constitutive equation of rock considering freeze-thaw and bedding Angle is derived.Through fitting analysis with experimental data and calculation of relevant parameters,the data fitting curve is drawn.The results show that the model can reflect the three stages of rock creep well,which proves the correctness and reliability of the constitutive model. |
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