Rheological Behaviour and Model for Porous Rocks Under Air-Dried and Water-Saturated Conditions
Rheological Behaviour and Model for Porous Rocks Under Air-Dried and Water-Saturated Conditions
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DOI：
10.2174/1874149500802010088
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发表时间：
2008-06
期刊：
影响因子：
--
通讯作者：
S. Okubo;K. Fukui;Xiujun Gao
中科院分区：
文献类型：
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作者：
S. Okubo;K. Fukui;Xiujun Gao
大多数岩石在变形过程中表现出粘弹性或随时间变化的行为。例如，在单轴压缩试验中，峰值强度和杨氏模量随着加载速率的增加而增加。在蠕变试验中，即使应力保持在预定值，应变也随时间增加。这种粘弹性行为在多孔岩石如凝灰岩和风化岩石中尤其显著。在这项研究中，我们首先提出了一个简短的回顾多孔岩石的粘弹性特性，然后提出了一个新的流变模型的基础上，本构方程的作者以前提出的。该模型由弹簧和阻尼器组成。我们假设，在以前的研究中描述的本构方程可以应用到弹簧。阻尼器的粘度在加载之前是低的，并且随着逐渐加载而逐渐增加。在低应力水平下的蠕变测试中，阻尼器的应变对应于蠕变应变，因为弹簧常数在低应力水平下不会显著降低。泥质砂岩，Oya凝灰岩，塔格凝灰岩和河津凝灰岩的实验分析与理论预测进行了比较。实测应力-应变曲线与理论曲线吻合较好。该模型较好地模拟了峰值强度和杨氏模量随加载速率的增加。这项研究的最重要的结果是，即使在低应力条件下，阻尼器的应变是相当大的比在以前的研究中考虑的。我们的模型提供了一个良好的模拟空气干燥和水饱和的条件下，在杨氏模量之间的差异，其中的差异被假定为反映到阻尼器的应变分区。在水饱和条件下，阻尼器的应变比在空气干燥条件下更快地增加，因此杨氏模量相对较小。
Most rocks exhibit viscoelastic properties or time-dependent behavior during deformation. For example, peak strength and Young's modulus increase with loading rate in uniaxial compression tests. In the creep test, strain increases over time even though stress is maintained at a predetermined value. Such viscoelastic behavior is especially notable in porous rocks such as tuff and weathered rocks. In this study, we first present a brief review of the viscoelastic properties of porous rocks, and then propose a new rheological model based on constitutive equations previously proposed by the authors. The model consists of a spring and a dashpot. We assume that the constitutive equation described in a previous study can be applied to the spring. The viscosity of the dashpot is low prior to loading, and increases gradually with progressive loading. In creep testing at low stress levels, strain of the dashpot corresponds to creep strain because the spring constant does not decrease significantly at low stress levels. Experimental analysis of muddy sandstone, Oya tuff, Tage tuff and Kawazu tuff is compared with theoretical predictions. The measured and theoretical stress-strain curves are in good agreement. The increase in peak strength and Young's modulus with loading rate is well simulated by the model. The most important result of this study is that even at low stress conditions, strain of the dashpot is considerably larger than considered in previous studies. Our model provides a sound simulation of the difference in Young's moduli between air-dried and water-saturated conditions, where the difference is assumed to reflect the partitioning of strain into the dashpot. In water-saturated conditions, strain of the dashpot increases more rapidly than in air-dried conditions, and Young's modulus is consequently relatively small.