Abstract The stiffness coefficient is a key parameter of rock fractures that controls the properties and behavior of a rock mass. According to the displacement discontinuity theory, the dynamic stiffness of rock fractures can be back analyzed using stress wave propagation. This study aims to measure the dynamic stiffness of rock fractures then develop an empirical ratio to describe the relationship between dynamic and static stiffness. Propped artificially fractured shale and granitic rock samples are employed. Mechanical and ultrasonic tests are conducted on two artificial rock fractures during uniaxial loading and unloading. As normal stress changes from 1 MPa to 50 MPa, the average dynamic normal stiffness of shale and granitic rock fractures changes from 330 GPa/m to 1960 GPa/m and from 90 GPa/m to 2320 GPa/m, respectively. For both artificial fractures, the dynamic stiffness is higher than the static stiffness but approaches the static stiffness with increasing normal stress. The ratio of dynamic to static normal stiffness is approximately 2.0 at a normal stress of 15 MPa; this ratio approaches 1.0 with increasing normal stress and varies widely under low normal stress. This study provides a method for evaluating the static or dynamic stiffness of rock fractures, which has important applications for seismic surveys or acoustic logs in the field of geological engineering.

中文翻译：

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可变正应力下支撑人工裂缝的动静刚度经验比

摘要 刚度系数是控制岩体性质和行为的岩石裂缝的关键参数。根据位移不连续理论，可以利用应力波传播反分析岩石裂缝的动态刚度。本研究旨在测量岩石裂缝的动态刚度，然后开发一个经验比率来描述动态和静态刚度之间的关系。使用支撑人工压裂的页岩和花岗岩样品。在单轴加载和卸载过程中对两个人造岩石裂缝进行机械和超声波测试。当法向应力从 1 MPa 变化到 50 MPa 时，页岩和花岗岩裂缝的平均动态法向刚度分别从 330 GPa/m 变化到 1960 GPa/m 和从 90 GPa/m 变化到 2320 GPa/m。对于这两种人工裂缝，动态刚度都高于静态刚度，但随着法向应力的增加而接近静态刚度。在 15 MPa 的法向应力下，动态与静态法向刚度之比约为 2.0；该比率随着法向应力的增加而接近 1.0，而在法向应力较低的情况下变化很大。该研究提供了一种评估岩石裂缝静态或动态刚度的方法，在地质工程领域的地震勘测或声波测井中具有重要应用。0 随着正应力的增加而变化很大，而在低正应力下变化很大。该研究提供了一种评估岩石裂缝静态或动态刚度的方法，在地质工程领域的地震勘测或声波测井中具有重要应用。0 随着正应力的增加而变化很大，而在低正应力下变化很大。该研究提供了一种评估岩石裂缝静态或动态刚度的方法，在地质工程领域的地震勘测或声波测井中具有重要应用。