统一强度理论应用于岩石的讨论

 具有多种形式的双剪理论已得到广泛的研究和应用，但没有基于试验数据的拟合与其他真三轴强度准则进行直接比较。以主应力形式直接构建线性和非线性统一强度理论，利用岩石的真三轴压缩、常规三轴压缩和伸长的试验结果，确定多个强度准则中的材料参数。统一强度理论对试验数据的拟合偏差较大，不能描述岩石常规三轴压缩和伸长强度随最小主应力的非线性增加，难以描述强度随中间主应力的变化趋势；而非线性理论使用2个隐式函数分段表示，实际计算时需进行多次比较判断。在最小主应力较低时，统一强度理论给出的岩石强度显著偏高，似乎不宜应用于孔壁崩落确定地应力、钻孔稳定性分析等。

DISCUSSION ON UNIFIED STRENGTH THEORIES FOR ROCKS

The twin-shear theory with a series of equations has not been compared directly with other true triaxial strength criteria on misfits for test data，although it has been studied thoroughly and applied widely in engineering. Linear and nonlinear unified strength theories are constructed with principal stresses. Parameters in various strength criteria are determined using true triaxial strengths，conventional compression and extension strengths as well. The theories present high mean misfits for test data，and cannot describe nonlinear increasing of conventional compression and extension strength with the minor principal stress，and the effect of the intermediate principal stress on strength. The nonlinear theory with two implicit equations of principal stresses is not friendly in calculation. The unified strength theories are not available in determining geostresses from borehole collapses and wellbore stability，as strength of rocks are extremely over-estimated at low minor principal stress.