Experimental Study On Time-Dependency Of Rock Under Uniaxial Compressive Load

The change rate of stress and strain in the rock engineering is not constant,the mechanical properties of rock under different loading rates are quite different,in addition,the change of stress and strain in the rock engineering is simultaneously,rather than only creep or relaxation.Therefore,loading rate dependency experiment and generalized relaxation experiment are performed on the Tage tuff and Jingkou sandstone in this page.The evolution law of mechanical parameters about the two kinds of rocks under different loading rates are analyzed,and the generalized relaxation characteristics of two kinds of rocks under different stress conditions are analyzed,which provide a theoretical basis and reference for evaluating the long-term stability of underground space structure and predicting the changes of stress and strain in rock engineering.Then obtain the fellowing conclusions:(1)Peak strength,peak strain,elastic modulus,failure life and failure pattern showed obvious loading rate dependence of Tage tuff and Jingkou sandstone.The increment of peak strength,peak strain,elastic modulus and the failure degree of Jingkou sandstone is more obvious compared to Tage tuff,when the loading rate increased.(2)The peak strength and the loading rate dependence coefficient n values of the Tage tuff(classⅠrock)and Jingkou sandstone(classⅡrock)under the condition of constant loading rate and alternating loading rate were studied.According to similar results,it is known that the method of alternating load rate test can also be used to study the load rate dependence of rock.(3)In the pre-peak stage,the higher the stress level of the rock specimen,the greater the change of ultimate stress and strain,and the initial strain rate and stress rate is greater of each α value.At the peak stress stage,the change of stress and strain is the greatest,and the rock samples have failured and macroscopic cracks formed on the samples’ surface under α=-0.3、-1.The generalized relaxation process can be divided into three stages: the rapid change of stress and strain,the low change of stress and strain and the failure of acceleration.(4)In the pre-peak stage,Under the same stress level,after the same time,the stress and strain change quantity of tage Tuff larger than Jingkou sandstone.When the stress level increases from 50% to 80% stress,Jingkou sandstones’ increase quantity of finial stress and strain variation is small than Tage tuff,and the initial strain rate and initial stress rate is also show the same law.Therefore,Time dependence of Tage tuff is lower than Jingkou sandstone.(5)Under different stress conditions,the isochrones of generalized relaxation is similar to the complete stress-strain curve of rock under uniaxial compression,and the isochrones of different time is contain in the complete stress-strain curve.The higher the stress value and the longer the rheological time is,the isochrones greater deviates from the complete stress-strain curve.