An Investigation On The Dynamic Shearing Properties Of Lithologic Material

Based on the experimental data on shaking table, this paper studies the dynamic shearing properties of lithologic material, involving dynamic mechanical properties, dynamic constitutive relation and influence mechanism. It provides scientific basis for the dynamic shearing strength parameters to be used for the dynamic analysis of rock body stability.By the results of cyclical direct shearing test with the frequency of 1HZ, 3 HZ and 5HZ, the author analyze the influence of frequency on shearing strength. It indicates that the parameter ' φ' almost keep constant with the change of frequency and the influence of frequency on shearing strength mainly achieved through its influence on the parameter'c'.The author put forword a theory of two effects about the influence mechanism of loading frequency on shearing strength. On the one hand, the effect of loading velocity of frequency cause the strength to increase;on the other hand, the effect of fatigue damage of frequency cause the strength to decrease. The final strength is decided by the summation of the above two effects. Moreover, resonance is also possible an influence factor on the shearing strength.Drawing a comparation between the results of cyclical direct shearing test with the frequency of 2HZ and the results of static, the author analyzes the sameness and difference. The sameness is that the decrease of carrying capacity after being sheared is mainly caused by the decrease of the parameter ' c', while the parameter 'φ' only chang a little. The difference is that the parameter ' c' under the condition of 2HZ is larger 30% than that under the condition of static, and that the closing stage of the static shearing stress-displacement curve will degenerate under dynamic condition. Then, by means of the effect of loading velocity, the author anlyze the reason that cuase the difference.Based on the results of 2HZ, the relation between energy loss and shearing displacement is researched, which indicates that the damage behavior exist in the whole course of the cyclic loading.By introducing a damage variable expressed by the equivalent shear stiffness, a dynamic shearing damage constitutive model of rock is established including three phases. Furthermore, the examination about the model indicates that it has some degree universal significance.