Fracture Characteristics And Damage Deterioration Mechanism Of Fractured Rock Mass Under Freeze-Thaw Cycles

In recent years,with the needs of national infrastructure construction in the western development,many large-scale rock mass projects will face freeze-thaw disasters in cold regions.The damage of F-T cycles will cause the deepening of rock fissures and the fracture failure behavior of rock.Therefore,in order to study the fracture characteristics and damage and failure mechanism of fractured rock mass under F-T cycles,this paper carried out relevant research from three aspects(laboratory experiments,microscopic analysis and theoretical derivation).The research contents are as follows :(1)Three-point bending tests of semicircular specimens with with different crack initiation angles under F-T cycles were carried out to reveal the effect of F-T treatment on rock fracture characteristics.In addition,the fracture morphology of SCB sample was obtained by 3D laser scanner and the fractal dimension was calculated.The results show that the fractal dimension value increases gradually with the increase of F-T cycles.(2)Experiments on double-notched sandstone specimens after different F-T cycles subjected to compression-shear tests were conducted to further investigate the effect of the F-T treatment on the mode II fracture toughness and fracture surface morphological characteristics.The results show that F-T cycles have an important role in the mode II fracture toughness and that the fracture toughness shows an obvious decreasing trend with an increase in F-T cycles(N).Moreover,the 3D surface of the fracture was reconstructed and scanned by electron microscopy.Parameters such as fractal dimension,asperity height,slope angle and3 DJRC values were calculated.The results indicate that the fracture surface becomes rougher with the increase of F-T cycles.(3)The stage analysis of sandstone compression-shear failure mode is carried out by AE technology.With the increase of the F-T cycles,the cumulative ringing count and the compaction time increased,and the elastic and yield failure stage time gradually decreased.At the same time,the RA-AF value and the nuclear density(KDE)cloud map of the compression-shear process were calculated,and it was found that the F-T cycles had a great influence on the distribution of the tension-shear signal in the compression and the yield failure stage,the number of signals increased and spread to the edge,but has less effect in the elastic phase.(4)According to thermodynamic theory and pore water frost heave deformation theory,a F-T damage degradation model based on porosity of fractured rock mass was established,and the porosity and pore size distribution of sandstone were measured by mercury intrusion method.The results showed that the effect of F-T cycles has a great influence on the porosity and pore size distribution of sandstone.Then,the parameters of the model are calculated according to the measured and thermodynamic parameters,and the model is verified with laboratory data,which is in good agreement with the experimental results.