Time-dependent brittle creep in Darley Dale sandstone
Time-dependent brittle creep in Darley Dale sandstone
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DOI：
10.1029/2008jb006212
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发表时间：
2009-07-11
影响因子：
3.9
通讯作者：
Main, I. G.
中科院分区：
文献类型：
--
作者：
Heap, M. J.;Baud, P.;Main, I. G.
岩石脆性变形随时间变化的特征是理解地壳长期演化和动力学的基础。孔隙水的化学影响通过应力腐蚀开裂促进时间依赖性变形，这使得岩石在远低于其短期破坏强度的应力下变形。在这里，我们报告的结果，在三轴应力条件下的Darley Dale砂岩（初始孔隙度，13%）的水饱和样品的时间依赖性脆性蠕变的研究。常规蠕变实验结果表明，轴向应变速率与所施加的差应力密切相关。差应力仅减少10%，应变率就减少两个数量级以上。然而，样品的自然变异性意味着必须进行多次实验才能得到一致的结果。因此，我们也证明了使用应力步进蠕变实验可以成功地克服这个问题。我们已经使用的应力步进技术，以调查在有效围压为10，30和50 MPa（同时保持恒定的20 MPa孔隙流体压力）的围压的影响。我们的研究结果表明，应力腐蚀过程中出现显着抑制在较高的有效压力，与蠕变应变速率降低了几个数量级。加倍的孔隙流体压力的影响，但是，同时保持一个恒定的有效围压，示出的影响范围内的应力腐蚀的速率从样品的变异性预期。我们讨论这些结果的背景下，微观结构分析，声发射震源位置，并适合建议的宏观蠕变规律。
The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the Earth's crust. The chemical influence of pore water promotes time-dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Here, we report results from a study of time-dependent brittle creep in water-saturated samples of Darley Dale sandstone (initial porosity, 13%) under triaxial stress conditions. Results from conventional creep experiments show that axial strain rate is heavily dependent on the applied differential stress. A reduction of only 10% in differential stress results in a decrease in strain rate of more than two orders of magnitude. However, natural sample variability means that multiple experiments must be performed to yield consistent results. Hence we also demonstrate that the use of stress-stepping creep experiments can successfully overcome this issue. We have used the stress-stepping technique to investigate the influence of confining pressure at effective confining pressures of 10, 30, and 50 MPa (while maintaining a constant 20 MPa pore fluid pressure). Our results demonstrate that the stress corrosion process appears to be significantly inhibited at higher effective pressures, with the creep strain rate reduced by multiple orders of magnitude. The influence of doubling the pore fluid pressure, however, while maintaining a constant effective confining pressure, is shown to influence the rate of stress corrosion within the range expected from sample variability. We discuss these results in the context of microstructural analysis, acoustic emission hypocenter locations, and fits to proposed macroscopic creep laws.