单参数的正则抛物线准则

NORMAL PARABOLIC CRITERION WITH A SINGLE PARAMETER

线性的Coulomb准则并不能完全描述岩石强度特征,有多种改进形式。剪切破坏的Mohr准则表现为应力圆的包络线,其待定参数难以从常规三轴压缩试验结果直接确定而研究较少。主应力形式的强度准则可分为显式和隐式,后者常以最大剪应力和平均主应力构造,且具有较高的相关系数和较小的拟合偏差。实际上显式和隐式准则的力学背景相同,可通过坐标系旋转互换。砂岩、大理岩等强度源于颗粒间黏结和摩擦,单参数的正则抛物线准则拟合强度与围压关系的精度优于两参数的Coulomb准则,而与Hoek-Brown准则相当。以正则抛物线准则拟合高围压下强度能够得到完整岩石的理想单轴压缩强度,进而与实际数值对比可确定岩石的初始损伤。

Linear Coulomb criterion can not completely describe the strength features of rock; and various revisions have been developed. The Mohr criterion on shear failure, which manifests as the envelope of failure stress circles, is studied rarely for the inconvenient to determine its parameters from the results of conventional triaxial compression test. Strength criteria with principal stresses form can be divided into explicit and implicit criteria. Implicit criteria is usually constructed with maximum shear stress and average principal stress, and has high correlation coefficient and low firing deviation for the evaluating index. Actually, the two criteria have the same mechanical background and can be alternated after the coordinate rotation. Strengths of rocks like sandstone and marble result from cohesion and friction among grains, and can be illustrated by the normal parabolic criterion with a single parameter, which is better than the Coulomb criterion and same as the Hoek-Brown criterion in fitting the relationship between strength and confining pressure. Ideal uniaxial compression strength of intact rock can be obtained by firing the strength with normal parabolic criterion under high confining pressure, and may be used to evaluate the initial damage after comparing the real magnitude of uniaxial compression strength.