Experimental investigation of frictional healing in granite: temperature-mineral composition interplay

Frictional healing of rock fractures is critical to the long-term stability of geological repositories for nuclear waste. This study investigates the influence of temperature on the frictional healing behavior of Inagawa and Inada granites using Slide-Hold-Slide (SHS) direct shear experiments conducted at 20 °C and 60 °C with hold periods ranging from 1 min to 5 days. The integrated analysis involved quantifying mechanical compaction during the hold phase and subsequent shear-induced dilation, monitoring chemical dissolution from the fracture interface, and applying rate-and-state friction (RSF) theory to characterize key parameters governing sliding stability. Experimental results demonstrate that at 20 °C, Inagawa granite exhibits a significantly higher frictional healing rate than Inada granite. Although elevating the temperature to 60 °C enhances healing in both granites, the increase is more pronounced in Inada granite. This behavior reflects lithology-dependent thermo–mechanical–chemical effects: the quartz- and feldspar-rich Inada granite shows a larger healing enhancement due to the higher thermal expansion coefficients and increased dissolution rates of these minerals at elevated temperature, whereas the biotite-rich Inagawa granite exhibits only a modest increase in healing rate owing to its lower thermal expansion coefficients and limited dissolution kinetics. Furthermore, rate-and-state friction (RSF) analysis indicates that Inagawa granite possesses a shorter cutoff time and higher cutoff velocity, suggesting that while it heals faster, it also has a greater potential for unstable slip. These findings provide mechanistic insights into the frictional stability of granite, highlighting the complex interplay of thermal, mechanical, and chemical (TMC) processes that govern the behavior of fractured rock.