The Effect of Varying Damage History in Crystalline Rocks on the P- and S-Wave Velocity under Hydrostatic Confining Pressure
The Effect of Varying Damage History in Crystalline Rocks on the P- and S-Wave Velocity under Hydrostatic Confining Pressure
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DOI：
10.1007/s00024-012-0550-0
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发表时间：
2013-04
影响因子：
2
通讯作者：
O. Blake;D. Faulkner;A. Rietbrock
中科院分区：
文献类型：
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作者：
O. Blake;D. Faulkner;A. Rietbrock
裂缝在许多岩土工程问题和地壳的许多过程中发挥着非常重要的作用。弹性波可以作为确定裂缝密度的遥感工具。定量研究了结晶岩中不同裂隙密度对P波、S波速度和围压下动弹性性质的影响。当一套干燥的西风花岗岩样品分别取为无侧限单轴强度的60%、70%、80%和90%时，监测了P波和S波速度的演变。然后将损伤试件置于2~200 Mpa的静水围压下，量化不同裂隙密度对P波和S波速度以及围压下弹性性质的影响。在单轴加载过程中，主要平行于加载方向的微裂纹的张开和扩展导致P波和S波速度分别下降0.5%和6.3%。在静水加载过程中，微裂纹在130℃的围压下闭合。在较低的压力下，样品中的裂纹损伤量具有很小但可测量的影响。我们观察到，在2 Mpa的围压下，由于裂缝密度的增加，P波和S波的速度分别系统性地降低了6%和4%。在50 Mpa时，P波和S波的总波速分别下降到2%和1%。微裂纹损伤量越大的试件，其弹性波速对压力越敏感。利用有效介质模型反演弹性波速，推断裂缝密度演化。对西风花岗岩试件的裂隙密度计算结果与实验数据的对比表明，所采用的有效介质模型给出了可解释和合理的结果。裂纹密度的变化可以解释为裂纹的闭合或张开以及裂纹的扩展。
Cracks play a very important role in many geotechnical issues and in a number of processes in the Earth’s crust. Elastic waves can be used as a remote sensing tool for determining crack density. The effect of varying crack density in crystalline rock on the P- and S-wave velocity and dynamic elastic properties under confining pressure has been quantified. The evolution of P- and S-wave velocity were monitored as a suite of dry Westerly granite samples were taken to 60, 70, 80 and 90 % of the unconfined uniaxial strength of the sample. The damaged samples were then subjected to hydrostatic confining pressure from 2 MPa to 200 MPa to quantify the effect of varying crack density on the P- and S-wave velocity and elastic properties under confining pressure. The opening and propagation of microcracks predominantly parallel to the loading direction during uniaxial loading caused a 0.5 and 6.3 % decrease in the P- and S-wave velocity, respectively. During hydrostatic loading, microcracks are closed at 130 MPa confining pressure. At lower pressures the amount of crack damage in the samples has a small but measureable effect. We observed a systematic 6 and 4 % reduction in P- and S-wave velocity, respectively, due to an increase in the fracture density at 2 MPa confining pressure. The overall reduction in the P- and S-wave velocity decreased to 2 and 1 %, respectively, at 50 MPa. The elastic wave velocities of samples that have a greater amount of microcrack damage are more sensitive to pressure. Effective medium modelling was used to invert elastic wave velocities and infer crack density evolution. Comparing the crack density results with experimental data on Westerly granite samples shows that the effective medium modelling used gave interpretable and reasonable results. Changes in crack density can be interpreted as closure or opening of cracks and crack growth.