Advances in development of shear-flow testing apparatuses and methods for rock fractures: A review

Understanding the mechanical and hydraulic properties of fractured rocks and their coupled processes is of great significance for the exploration, design, construction, operation, and maintenance of many rock engineering projects such as hydropower development, oil and gas extraction, and underground waste disposal. With the rapid advancement of global and national strategies such as the “Paris Agreement” and the “Belt and Road Initiative”, more and more projects are developed in the complex geological environment with varying geological structures. Shear failure and rock instability are prone to occur in fractured rock masses under the coupled effects of high stress, high pore pressure, and engineering disturbance, which are main sources for engineering disasters such as roof collapse and caving, water and mud inrushes, and induced earthquakes. To solve these problems, extensive research on the coupled shear-flow behavior of fractures has been conducted. However, due to the complex mechanical, hydraulic and geometrical characteristics of single fractures and fracture networks, a large number of outstanding issues related to the impact of the coupled processes on the engineering characteristics of rock masses are still unsolved. The relevant experimental apparatuses and methods remain to be further developed. Therefore, in this review, we analyze and summarize the existing shear-flow experimental apparatuses, classify apparatus configurations, specimen shapes, and testing principles, and compare their advantages and disadvantages. We also summarize the main scientific findings obtained from various experimental apparatuses, aiming to provide a reference for developing new shear-flow experimental apparatuses and conducting related scientific research in the future.