河津凝灰岩广义应力松弛特性及数值模拟研究

Generalized relaxation properties and numerical simulation of Kawazu tuff

在很多地下工程实践中,岩体既不是纯蠕变,也不是纯应力松弛,而是随着时间的增加,应力和应变同时发生变化,表现出时间依存性,导致岩体最终破坏,这种现象用一般的蠕变和应力松弛很难解释清楚。全面系统地阐述了广义应力松弛特性及其工程物理意义,借用非线性Maxwell模型,求解了广义应力松弛条件下可变模量本构方程解析解,特别提出了通过交替荷载速率试验和加、卸载试验,精确求解峰前区域荷载速率依从性系数n_1的新方法。进行了70%和90%应力水平下广义应力松弛试验,并讨论和分析了不同应力水平、不同方向系数下广义应力松弛试验的时间依存性,最后用基于非线性Maxwell模型的可变模量本构方程对70%和90%应力水平下的广义应力松弛试验进行了数值模拟,结果表明,计算和试验结果一致性较好,很好地解释了河津凝灰岩广义应力松弛特性。

In many practices of underground engineering, rock mass is subjected to neither pure creep nor pure relaxation. In fact, both stress and strain change with the lapse of time, and thus rock mass has time-dependent property, which eventually lead to fracture of rock mass. It is hard to exhaustively explain this phenomenon by creep and relaxation. This study comprehensively describes the characteristics of generalized stress relaxation and the significance of engineering practices. Non-linear Maxwell model is applied to solve the exact solutions of variable compliance type constitutive equation under the generalized relaxation condition. In particular, we obtain the accurate value of parameter-n1 which governs the time-dependent behavior in the pre-failure region by alternately loading rate and loading-unloading tests. Generalized relaxation tests are carried out under 70% and 90% stress levels, and the time-dependent behavior under different stress levels and different direction coefficients are also discussed. Finally, experimental results of generalized relaxation under 70% and 90% stress levels are numerically simulated by the variable-compliance-type constitutive equation based on the non-linear Maxwell model. Calculated results are good agreement with experimental data, and the properties of generalized relaxation of Kawazu tuff are well explained.