COMPARATIVE STUDY OF CONVENTIONAL MECHANICAL,CREEP AND STRESS RELAXATION PROPERTIES OF SILTY MUDSTONE UNDER TRIAXIAL COMPRESSION

The conventional mechanical,creep and stress relaxation tests of saturated silty mudstone are carried out under triaxial compression with same confining pressure.Based on the test results,the axial strengths of the specimens in three mechanical tests are compared;and the peak axial strains of the specimens are also compared.Then the differences of axial strengths and peak axial strains of the specimens among tests are explained from the view point of rock failure mechanism respectively.Burgers model is selected to describe the creep and stress relaxation properties of silty mudstone.According to the identification results,shear moduli G of the specimens obtained from the conventional mechanical test are compared respectively with instantaneous shear moduli G1 of the specimens identified by the creep model and the stress relaxation model,and the parameter values of the creep model are compared with those of the stress relaxation model.The analysis results show that:(1) The axial strength of the specimens in the conventional mechanical test is the highest,followed by the creep test,and that in the stress relaxation test is the lowest.(2) The peak axial strain of the specimens in the conventional mechanical test is the highest,followed by the stress relaxation test,and that in the creep test is the lowest.(3) Shear modulus G is 64.5 times larger than instantaneous shear modulus G1 of the creep model,and 86.8 times larger than instantaneous shear modulus G1 of the stress relaxation model.(4) Through comparing the values of G1,G2,?1 and ?2 between the creep model and the stress relaxation model,it is found that each of four parameter values of the creep model is larger than that of the stress relaxation model.It is also found that the values of G1of the two models are close,and that the differences among the orders of magnitude of the values of G2,?1 and ?2 of the two models are 1 to 2 series.The difference in the values of G2 is the largest and the difference in the values of ?1 is the smallest between the two models.Moreover,it is shown that the differences in the values of ?1 and ?2 are larger than those of G1 and G2 between the two models.The results indicate that ?1 and ?2 have a great effect on the creep and stress relaxation properties of silty mudstone.(5) The results of comparison between the two models verify the correctness of the creep and stress relaxation parameters.The results show that the creep properties of silty mudstone are not equivalent to its stress relaxation properties,the stress relaxation properties of silty mudstone can?t be deduced simply from its creep properties,which is different from linear viscoelastic materials.