Hydraulic Fracturing and Self-Healing Behavior in Compacted Bentonite: Insights from Visualization Experiments

Abstract

Understanding the hydraulic fracturing and self-healing behavior of compacted bentonite is essential for the long-term performance evaluation of engineered barriers in deep geological disposal. In this study, cyclic hydraulic fracturing and self-healing tests were conducted on Gaomiaozi (GMZ) bentonite at different dry densities using a self-developed visualization apparatus, with varying healing durations in each cycle. The evolution of healing state with healing duration was discussed from the perspectives of the variations of fracturing resistance and macrofracturing path. Moreover, postmortem analyses were performed on selected subsamples to investigate the final physical states and microstructure. Results revealed an initial logarithmic linear growth in fracturing resistance with healing duration, independent of dry density. Subsequently, fracture resistance no longer increased but stabilized within a certain range, which was defined as the “subhealing” state. The “true-healing” state was considered as new fractures ceasing to form along the original fracturing path. Specimens with a dry density of 1.7 g/cm3 required 45 h to reach the subhealing state but did not achieve the true-healing state even after a healing stage of 363 h. This behavior may be attributed to the initial fracturing area containing greater interaggregate pores than the area away from the initial fracturing one. Nevertheless, specimens with a dry density of 1.5 g/cm3 reached the subhealing state within 3 h and achieved the true-healing state after 45 h. The stabilized fracturing resistance was approximately 23%–42% of the initial resistance. Based on these findings, this study also sheds light on the predictions of the long-term fracturing resistance of specimens with varying dry densities and the time required to reach the subhealing state.