三轴应力作用下水对岩石应力松弛特性影响作用试验研究

 采用RLJW–2000岩石三轴流变伺服仪，在相同试验条件下分别对干燥与饱水状态下的粉砂质泥岩进行室内三轴压缩应力松弛试验。依据试验结果，分析了松弛稳定后水对岩石总应力松弛量、总应力松弛度、松弛稳定时间、平均应力松弛速率的影响作用，并且分析了松弛过程中随时间的增加水对岩石应力松弛量、应力松弛度、应力松弛速率影响作用的变化趋势。考虑粉砂质泥岩流变参数的损伤劣化效应，以Hooke-Kelvin模型为基础，引入损伤变量对模型进行改进，建立了岩石的非线性应力松弛损伤模型。应用Levenberg-Marquardt算法，辨识得出干燥与饱水岩石的应力松弛损伤模型参数。基于辨识结果，研究了水对岩石非线性应力松弛损伤模型参数的影响作用。研究结果表明：(1) 由于水的影响作用，松弛稳定后粉砂质泥岩的总应力松弛量减少、总应力松弛度增大、松弛达到稳定的时间增长；松弛过程中，随时间的增加，水对粉砂质泥岩应力松弛量与应力松弛度的影响作用减弱。(2) 由于水的影响作用，粉砂质泥岩的平均应力松弛速率减小，各时刻岩石的应力松弛速率降低；松弛过程中，随时间的增加，水对粉砂质泥岩应力松弛速率衰减的影响作用增强。(3) 粉砂质泥岩应力松弛过程中，水对岩石的黏性力学特性影响作用较大，而对岩石的瞬时弹性和黏弹性力学特性影响作用相对较小。(4) 粉砂质泥岩的应力松弛损伤受应变水平、时间以及水3种因素的共同影响，而非线性应力松弛损伤模型可以有效地反映3种因素对岩石应力松弛参数的综合损伤弱化作用。(5) 水对粉砂质泥岩应力松弛特性的影响作用是极其显著的，水极大地增强了岩石的时效特征，改变了粉砂质泥岩的应力松弛特性。因此，在重大工程设计和施工中，不能忽视水对岩石应力松弛特性的影响作用。

EXPERIMENTAL STUDY OF INFLUENCE OF WATER ON STRESS RELAXATION OF ROCK UNDER TRIAXIAL STRESSES

The stress relaxation tests of dry and saturated silty mudstone under triaxial compression were performed with the servo-controlled rheology testing machine RLJW–2000. The effects of water on the magnitude，the level and the time of the total relaxation and the average relaxation rate were analyzed according to the experimental results. A damage variable was proposed to consider the weakening of rock parameters. A new nonlinear damage model was established by introducing the damage variable into Hooke-Kelvin model. The Levenberg-Marquardt algorithm was adopted to identify the model parameters of dry and saturated rock. The effects of water on the parameters of the nonlinear damage model were studied according to the results of identification. For water saturated rock，the total relaxation decreases but the degree and the time of the total relaxation increase after stress relaxation. The effects of water on the magnitude and level of relaxation are reduced with time increasing during the period of stress relaxation. The average rate of relaxation and the rate of relaxation at different time decrease due to the effect of water，and the effect of water on the reduction of relaxation rate of rock increases with the increasing of time during the stress relaxation. The viscosity of rock was affected significantly by water and the instantaneous elastic and viscoelastic properties of rock are less affected. The damage of rock due to stress relaxation is related to these factors，the strain level，the time and the occurrence of water. The nonlinear damage model effectively reflect the deterioration of rock properties induced by these factors. Overall，water has significant effects on the properties of stress relaxation of silty mudstone，which should not be ignored in design and construction of major projects.