Harbord C, Brantut N, David E C, Mitchell T M
Department of Earth Sciences, University College London, Gower Place, London WC1E 6BT, United Kingdom.
Rev Sci Instrum. 2022 May 1;93(5):053908. doi: 10.1063/5.0084477.
A new setup to measure acoustic wave velocities through deforming rock samples at high pressures (up to 1000 MPa), temperatures (up to 700 °C), and differential stresses (up to 1500 MPa) has been developed in a recently refurbished gas medium triaxial deformation apparatus. The conditions span a wide range of geological environments and allow us to accurately measure differential stress and strains at conditions that are typically only accessible in solid medium apparatus. Calibrations of our newly constructed internal furnace up to 1000 MPa confining pressure and temperatures of up to 400 °C demonstrate that the hot zone is displaced downward with increasing confining pressure, resulting in temperature gradients that are minimized by adequately adjusting the sample position. Ultrasonic velocity measurements are conducted in the direction of compression by the pulse-transmission method. Arrival times are corrected for delays resulting from the geometry of the sample assembly, and high-precision relative measurements are obtained by cross correlation. Delays for waves reflected at the interface between the loading piston and sample are nearly linearly dependent on differential applied load due to the load dependence of interface stiffness. Measurements of such delays can be used to infer sample load internally. We illustrate the working of the apparatus by conducting experiments on limestone at 200 MPa confining pressure and room temperature and 400 °C. Ultrasonic data clearly show that deformation is dominated by microcracking at low temperature and by intracrystalline plasticity at high temperature.
在最近翻新的气体介质三轴变形装置中，开发了一种新装置，用于在高压（高达1000兆帕）、高温（高达700°C）和差应力（高达1500兆帕）下通过使岩石样品变形来测量声波速度。这些条件涵盖了广泛的地质环境，使我们能够在通常只有固体介质装置才能达到的条件下准确测量差应力和应变。对我们新建造的内部炉在高达1000兆帕围压和高达400°C温度下的校准表明，随着围压增加，热区向下移动，通过适当调整样品位置可将温度梯度降至最低。通过脉冲传输法在压缩方向上进行超声波速度测量。对由样品组件几何形状导致的延迟进行到达时间校正，并通过互相关获得高精度相对测量值。由于界面刚度与载荷有关，加载活塞与样品之间界面处反射波的延迟几乎与施加的差载荷呈线性相关。测量这种延迟可用于推断样品内部的载荷。我们通过在200兆帕围压、室温以及400°C下对石灰岩进行实验来说明该装置的工作情况。超声波数据清楚地表明，在低温下变形以微裂纹为主，而在高温下以晶内塑性为主。
