Study On Creep Damage Evolution Mechanism Of Freeze-Thaw Shale In Slope In Seasonal Freezing Area

More than half of the country is covered by seasonal and permanent permafrost,and as large key projects in these areas are launched one after another,the repeated action of freeze-thaw on the fractured rock masses cannot be avoided.Under the action of freeze-thaw cycles（F-T）,the rock mass suffered damage deterioration,which will easily lead to geological disasters such as F-T spalling,landslides and slides on slopes,seriously affecting the engineering safety of slopes.Therefore,it is a critical issue in the field of slope stability research in seasonal permafrost to discuss the creep damage characteristics and creep damage evolution mechanism of rocks considering the effects of F-T.This paper takes the slope of the Shihuang site in Gaojiabao town,Shaanxi province,as the engineering background,and selects a typical black mud shale as the research object to conduct freeze-thaw cycle tests on rocks with different cycle times and F-T temperature differences.The creep damage model was finally established by considering the F-T temperature and the number of cycles,and the creep model was applied to the numerical calculation of the stability of the slope of the site.The main research results are as follows:（1）The pore characteristics of the shale in the unfrozen-thawed state are dominated by tiny pores,while a small number of medium pores are distributed.As the F-T cycle progresses,the peak strain of the rock gradually increases.The NMRT₂ spectra shows that with the increase number of F-T cycles and the F-T temperature difference,pore structure of the rock samples shows an increasing pore size and the number of pores,and the average porosity also tends to increase accordingly.（2）The steady-state creep rate and creep deformation of the rock gradually increased with the increase in the number of F-T cycles and axial pressure as well as the decrease in freezing temperature,while the long-term strength of the rock tends to decrease significantly.In contrast,found that with the increase of axial stress level,the F-T temperature difference had a relatively small effect on the amount of axial creep deformation and creep rate of shale,while the number of F-T cycles had a relatively large effect.（3）Based on the experimental results,a damage variable considering the coupling of freeze-thaw and creep was proposed;a non-linear fractional-order creep damage model considering both F-T temperature and number of cycles was established based on the strain equivalence principle,mediated by rock porosity variation and damage area,and the applicability and reliability of the model was verified by the least-squares method of parameter identification based on pattern search.（4）The stability of slope was determined by calculating the slope safety coefficient,and then the stability of the slope of Shanxi Imperial Terrace under different freeze-thaw conditions was simulated and analyzed through the model established by the experiment.The second layer of the brick wall is found to be a more dangerous area and two potential sliding surfaces extend from the loess layer in the upper part of the slope to the first step,so additional support is required to ensure the long-term stability of the slope.