岩石指数型强度准则在主应力空间的特征

CHARACTERISTICS OF EXPONENTIAL STRENGTH CRITERION OF ROCK IN PRINCIPAL STRESS SPACE

指数型强度准则利用显式函数表示最小主应力和中间主应力对强度的影响,强度准则参数具有明确的力学含义;常规三轴压缩强度表明,随着正应力增大,剪切强度趋于常数,而破裂角趋于45°;但Mohr应力圆与外包络线在切点附近差异较小,且岩石并非均匀各向同性材料,实际破裂角与理论破裂不会完全一致。真三轴试验数据的离散性较大,强度准则参数对拟合偏差的影响并不显著,而以最小拟合偏差确定的参数未必体现岩石的真实力学性质。在研究强度准则在主应力空间内的力学特征之后,建议依据应力趋于无限时中间主应力与最小主应力对强度的影响系数在σ2=σ3处相等来确定强度准则参数,由此得到的拟合误差并未显著增大。

The exponential strength criterion with direct form denotes influences of the minor principal stress and intermediate principal stress on strength. The parameters in the strength criterion have definite mechanical background. Based on the conventional compression strength, the shear strength tends to be constant as normal stress increases; and the crack angle predicted by Molar circle is closed to 45°. However, the practical crack angle may not agree with the theoretical value because of small difference between envelope and Mohr circle near the tangent point and the heterogeneity of rock. The parameters in strength criteria are not sensitive to fitting errors because of dispersion of test data in the true triaxial compression; the best fitting solution determined by the minimum fitting error may not be able to describe the strength property of rock correctly. The characteristics of exponential strength criterion in principal stress space are studied. It is suggested that the parameters in strength criterion should be determined based on the fact that the influential index of the minor principal stress is equal to that when the intermediate principal stress is equal to the minor principas stress under the condition that the stress tends to be infinite. And the misfit of test data does not significantly increase.