| In recent years,with the intensification of global warming,the number of positive and negative temperat.alternations has increased every year,and the freezing and thawing environment of rock masses has gradually changed.In this case,it is particularly important to study the physical and mechanical properties of rock masses under different freeze-thaw conditions.In this paper,red sandstone is taken as the research object,and short-cycle freeze-thaw cycle tests and conventional freeze-thaw cycle tests are performed on the red sandstone.Specific surface area and pore diameter analysis tests of red sandstone after different freeze-thaw methods,uniaxial compression under dynamic and static mechanics The experiments analyzed the physical and microscopic characteristics and dynamic and static mechanical properties of red sandstone under different freeze-thaw modes.By analyzing the energy characteristics of red sandstone during uniaxial compression,the in-depth study of the damage and damage to rock mass by different freeze-thaw methods was conducted.Finally,the PFC discrete element software was used to simulate the change of mechanical properties of red sandstone under uniaxial compression.The following conclusions were reached:?1?Under short-cycle multi-frequency freeze-thaw cycles?0150 times?,the apparent appearance of red sandstone did not change significantly,but its mass loss rate decreased first?060 times?and then increased?60150 times?with the increase of freeze-thaw cycles.Under normal freezing and thawing,the red sandstone appears slag phenomenon after 20 times,and with the increase of the number of freeze-thaw cycles,the surface shows peeling phenomenon,and the quality loss rate is first reduced?020 times?After the increase?2060 times?.?2?Under the action of short-cycle multi-frequency freeze-thaw,the pore volume of red sandstone increases smoothly before 60 times and increases stepwise after 60times;under conventional freeze-thaw action,the pore volume of red sandstone increases relatively before 20 times The relative increase after the second is small.?3?As the number of short-cycle multi-frequency freeze-thaw cycles increases,the compressive strength of red sandstone increases first and then decreases,the elastic modulus decreases gradually,and the peak strain increases first and then decreases;and The compressive strength,elastic modulus and the number of short-cycle multi-frequency freeze-thaw cycles have a good quadratic function relationship.As the number of conventional freeze-thaw cycles increases,the compressive strength,elastic modulus and peak strain of red sandstone all increase first and then decrease;Good linear function relationship.When the multiple freeze-thaw cycles in a short period exceed 4.5 times within the period of one conventional freeze-thaw period,the damage of the rock will exceed that of the conventional freeze-thaw period.?4?After undergoing two freeze-thaw cycles,the compressive strength of red sandstone increases with the increase of the strain rate as a whole and then changes smoothly;The minimum is at the strain rate of 1×10-55×10-5,and the maximum is at the strain rate of 1×10-35×10-3;the strain rate and the compressive strength of red sandstone after freezing and thawing conform to an exponential function relationship,and the fitting effect is good.Short-cycle multi-frequency freeze-thaw at 060 times:Strain rate 5×10-51×10-33 is the significant response stage of compressive strength of red sandstone,when freeze-thaw at 60150 times:Strain rates ranging from 5×10-5to 5×10-33 are in the stage of significant response of red sandstone compressive strength.The strain rate of 5×10-55×10-44 under the conventional freeze-thaw action is the stage of significant response of the compressive strength of red sandstone.?5?After the freeze-thaw cycles of two different freeze-thaw modes,the energy storage limit of red sandstone increases first and then decreases as the number of freeze-thaw cycles increases.As the freezing and thawing times of the two freezing and thawing methods increase,the unit strain accumulation energy of red sandstone in the compaction stage,elastic stage and plastic stage all shows a decreasing trend.The proportion of accumulated energy per unit strain to the total energy per unit strain shows a downward trend as a whole.?6?Using PFC numerical simulation software,the analysis shows that as the number of freeze-thaw cycles increases,the total number of cracks generated by the model sample gradually increases;as the number of short-cycle multi-frequency freeze-thaw cycles increases,the crack fractal dimension of the model sample Gradually increasing,the degree of damage of the model sample gradually increases;with the increase of the number of conventional freeze-thaw cycles,the crack fractal dimension of the model sample gradually increases at the time of 0-20 freeze-thaw cycles,at 20-60 It is gradually reduced at the second time;the damage degree of the model sample is the largest at 20 times of conventional freezing and thawing. |
PDF Full Text Request