中主应力对粗粒料强度有重要影响,而强度研究中常用的大型三轴试验不能考虑中主应力对粗粒料强度的影响。通过大型真三轴各向等压固结等比例加载试验,研究了三维应力状态下粗粒料的强度特性。试验结果表明:随着中主应力系数b的增大,粗粒料大小主应力之差的峰值也逐渐增大,特别是中主应力系数从0增大到0.25时,大小主应力之差的峰值的增大幅度较大,增加了近50%。Lade-Duncan准则较好地描述了粗粒料内摩擦角的变化趋势,不过高估了内摩擦角;SMP准则较好地反映了中主应力系数从0增大到0.25时的内摩擦角的数值大小,但中主应力系数>0.25之后,SMP准则计算的内摩擦角基本随着b的增大而减小,低估了粗粒料的内摩擦角。提出采用的Lade-Duncan准则与SMP准则相结合的单参数复合强度准则,较好地反映了粗粒料强度的数值大小和变化趋势。提出的强度准则在三维主应力空间呈三角锥曲面族形状,轴对称应力状态下的内摩擦角越小,强度越小,三角锥曲面越小,锥角越浑圆,越接近于圆形,而内摩擦角越大,强度越大,三角锥曲面越大,锥角越尖锐,越接近于正三角形。

The intermediate principal stress has an important effect on the strength of coarse granular materials. However, the large-scale triaxial tests commonly used in strength study does not consider the effect of intermediate principal stress on the strength of coarse granular materials. Large-scale true triaxial tests under isotropic consolidation and proportional loading conditions were conducted to investigate the strength properties of coarse granular materials under three-dimensional stress states. Test results show that the peak value of the difference between major and minor principal stress of coarse granular material increases with the increasing of the coefficient (b) of intermediate principal stress, especially when b increases from 0 to 0.25 the peak value of the difference between major and minor principal stress increases nearly 50% compared to strength under axisymmetric triaxial stress state. Lade-Duncan failure criterion well describes the variation trend of internal friction angle for coarse granular materials; but overestimates the internal friction angle. SMP failure criterion commendably depicts the numerical value of internal friction angle when b increases from 0 to 0.25; when b is larger than 0.25, however, the results of SMP criterion decrease with the further increasing of b, which underestimates the internal friction angle. In view of this, a one-parameter composite strength criterion combining Lade-Duncan criterion and SMP criterion was proposed based on test results. The proposed criterion well reflects the numerical value and variation trend of the strength of coarse granular materials. The proposed strength criterion is shown as a triangular conical surface in three-dimensional principal stress space. The strength and triangular conical surface are small and the cone angle tends to be circle when the internal friction angle under axisymmetric stress state is small; with the increasing of internal friction angle, the strength and triangular conical surface gradually become larger and the cone angle tends to be triangular.