Experimental Research On The Damage Characteristics Of Triassic Sandstone After Freezing-hawing Circles In Fugu District

The Fugu district,Shaanxi province,is located at the north in Jinshan gorge area of the Yellow River.Geological hazards tend to happen in the slope in that place,which has resulted in severe influences to the economic development.Therefore,it is of great theoretical and practical significance to carry out experiments to study the effect of freeze-thaw cycle on the physical and mechanical properties of rock mass in this district and its damage mechanism.In this paper,the Triassic sandstone in the Fugu district was as the study object,and the macromicrophysical and mechanical properties of the sandstone under the influence of freeze-thaw cycle with different temperatures and frequencies were carried out.Based those experiments,the damage evolution characteristics of the sandstone was analyzed.The main research results are as follows:(1)Based in the tests of the physical properties of the sandstone at different experimental conditions,the longitudinal wave velocity and resistivity decreased with the increase of the freeze-thaw cycle frequencies,but increased for the saturation mass,nuclear magnetic T2 spectrum distribution,area of nuclear magnetic peak,and porosity.(2)In terms of the results of uniaxial compression tests and Brazilian cleavage tests at conditions of after 30 freeze-thaw cycles at-20～20 ℃,the sandstone’ uniaxial compressive strength,peak tensile strength,and elastic modulus decreased when the freeze-thaw cycle frequencies increased,while the peak strain increased first and then decreased.(3)According to the damage theory of rock mechanics,the relation between the physical and mechanical properties of the sandstone was studied,which was building on the definition of evaluation index of deterioration degree and the establishment of the damage variables.An exponential relationship was shown between the freeze-thaw cycle frequencies and each damage variable of the density,p-wave velocity,resistivity,nuclear magnetic resonance,compressive strength,tensile strength,and shear strength.The value of these damage variables increased with the increase of the freeze-thaw cycle frequencies,namely an intensify of the damage degree of the sandstone.