Permeability measurements were made on sandstone during confined Brazilian strength tests. The test involves 50 mm diameter disk-shaped, jacketed samples that are subjected to confining stresses while they are diametrically loaded. Specially designed end caps allow for concurrent gas flow measurements. The test configuration allows for the samples to be subjected to a range of stresses, with the confining stress as the intermediate principal stress. The majority of the tests measured permeability during loading to failure in the confined extension region. The permeability of the sandstone sample increases significantly well before the peak load is reached due to newly formed microcracks that continue to coalesce and dilate with further loading. Permeability increases are inversely proportional to the intermediate principal stress as increased confining pressures suppress growth, coalescence, and dilation of microcracks. Additional testing includes unloading and reloading cycles prior to failure. With each unloading–reloading cycle, permeability at comparable stresses is increased compared to the previous cycle, consistent with increasing damage in the form of an expanding microcrack network.

渗透率测量是在巴西限制强度测试期间对砂岩进行的。该测试涉及直径为 50 毫米的圆盘形夹套样品，这些样品在径向加载时会受到围压。专门设计的端盖允许同时进行气体流量测量。测试配置允许样品承受一定范围的应力，其中围压作为中间主应力。大多数测试测量了在受限延伸区域加载到失效期间的渗透率。砂岩样品的渗透率在达到峰值载荷之前显着增加，这是由于新形成的微裂纹随着进一步载荷而继续聚结和扩张。渗透率的增加与中间主应力成反比，因为增加的围压抑制了微裂纹的生长、聚结和扩张。附加测试包括故障前的卸载和重新加载循环。随着每个卸载-重新加载循环，与前一个循环相比，可比应力下的渗透率增加，这与扩展微裂纹网络形式的损坏增加一致。