Experimental Investigation on Fracture Self-Sealing of Clay Rock

Clay rock is considered a host rock for the geological disposal of high-level radioactive waste. It is crucial to investigate the self-sealing behavior of fractures within the rock under various conditions such as deviatoric stress and temperature. Furthermore, analyzing the microstructural changes provides valuable insights into the self-sealing mechanism of claystone fractures and contributes to the long-term safety evaluation of underground repositories. In this study, specimens containing central holes were prepared in both bedding-normal and bedding-parallel directions, along with rocks containing prefabricated cracks. By conducting central-hole permeability tests on specimens with prefabricated cracks, factors influencing the permeability of clay rocks were investigated, including resaturation degree, confining pressure, and temperature, with particular emphasis on the effects of resaturation and deviatoric stress. Subsequently, a microstructural analysis was performed for undisturbed and self-sealed specimens (normal and parallel to the bedding planes) under hydration swelling, stress, temperature, and other relevant factors, focusing on the regions both inside and outside the central holes. The results showed that: (1) hydration swelling parallel to the bedding planes is more pronounced and faster, independent of the specimen’s initial moisture content; (2) the specimen experiences volumetric compression and decreased permeability under confining pressure; (3) the increase in the rock hydraulic conductivity is primarily attributed to changes in fluid viscosity coefficient and density due to the elevated temperature; (4) the permeability decreases progressively with the volumetric strain compression under deviatoric stress, while claystone permeability exhibits a slightly increasing trend following expansion; and (5) the fracture self-sealing characteristics display significant microstructural anisotropy in both directions. These findings provide insights for uncovering the self-sealing mechanism of claystone cracks and evaluating the long-term performance of underground repositories.