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采用分级加载方法,对三峡地区巴东组粉砂质泥岩开展峰前、峰后三轴压缩应力松弛试验。依据试验结果,分析峰前弹性段、屈服段,峰后应变软化段、残余强度段岩石应力松弛量、应力松弛度、松弛稳定时间以及应力松弛速率的变化规律,研究峰前、峰后不同阶段岩石应力松弛特征的差异。引入损伤变量对三参量广义Kelvin模型进行改进,建立岩石的非线性应力松弛损伤模型。应用Levenberg-Marquardt算法,辨识得出岩石的应力松弛损伤模型参数。基于辨识结果,分析峰后破裂对岩石应力松弛模型参数的影响作用,研究峰前、峰后不同阶段岩石应力松弛模型参数的变化规律。在试验研究成果的基础上,总结得出峰前、峰后岩石不同的应力松弛机制。研究结果表明:(1)峰前、峰后各阶段中,峰后应变软化段试样的应力松弛量大,应力损失程度高,松弛稳定时间长,应力松弛速率快,工程实践中应尽可能避免使岩石处于峰后应变软化段。(2)峰后各级应变水平试样的G1,G2,H1参数值为峰前0.20%应变水平相应参数值的1%~53%,峰后岩石的应力松弛模型参数值急剧降低。(3)峰后形成的宏观破裂对试样的黏弹性力学特性影响最大,黏性力学特性其次,而对试样的瞬时弹性力学特性影响最小。(4)峰后应变软化段试样的G1,H1模型参数值大幅降低,峰前屈服段试样的G2模型参数值大幅降低。(5)峰前岩石的应力松弛主要是由于岩石内部微裂隙的产生、扩展等原因而引起的,峰后岩石的应力松弛主要是由于岩石中宏观裂纹的产生、扩展以及贯通等原因而引起的。峰前、峰后岩石的应力松弛机制不同。
The stratified loading method was used to carry out the triaxial compression stress relaxation test of the Badong Formation silty mudstone in the Three Gorges area. According to the experimental results, the variation regularity of elastic relaxation, yielding, post-peak strain softening, post-peak rock stress relaxation, stress relaxation, relaxation relaxation time and stress relaxation rate were analyzed. Differences of rock stress relaxation characteristics. The damage variable is introduced to improve the three-parameter generalized Kelvin model, and a nonlinear stress relaxation damage model of the rock is established. The Levenberg-Marquardt algorithm is used to identify the stress relaxation damage parameters of the rock. Based on the recognition results, the effect of post-peak fracture on the parameters of rock stress relaxation model is analyzed. The variation regularity of rock stress relaxation model parameters before and after peak is studied. Based on the experimental results, the different stress relaxation mechanisms of rocks before and after the peak are concluded. The results show that: (1) In the pre-peak and post-peak phases, the sample after stress relaxation has a large amount of stress relaxation, high stress loss, long relaxation time and high stress relaxation rate, and should be practiced in engineering practice Avoid rock after the peak strain softening section. (2) The G1, G2 and H1 parameters of strain level at all levels after the peak are between 1% and 53% of the corresponding values of the 0.20% strain level before the peak, and the parameters of the stress relaxation model of the post-peak rock decrease sharply. (3) The macroscopic rupture formed after the peak has the greatest influence on the viscoelastic mechanical properties of the specimen, followed by the viscoelasticity and the least impact on the transient elastic properties of the specimen. (4) The parameter values of G1 and H1 in the strain-softened section after the peak are significantly reduced, and the parameters of the G2 model in the yield section before the peak are greatly reduced. (5) The stress relaxation of the pre-peak rock is mainly caused by the generation and expansion of micro-cracks in the rock. The stress relaxation of the post-peak rock is mainly caused by the generation, expansion and penetration of macro-cracks in the rock . Before and after the peak rock stress relaxation mechanism is different.