An Experimental Investigation on the Creep Behavior of Deep Brittle Rock Materials

The stability of deep rock engineering, especially during the excavation, is inextricably linked to the time-dependent mechanical properties of brittle rock. Therefore, the uniaxial creep test in a multilevel loading path is carried out, accompanying the real-time DIC (digital image correlation) and AE (acoustic emission) technologies. For the quartz sandstone, the lateral strain is more sensitive to increasing stress levels, and the lateral ductility is more significant during the creep process. The saturated quartz sandstone shows a certain bearing capacity before the volumetric dilation predominance. The softening effect of moisture causes a nearly invariable Poisson's ratio during the middle stress stages, as well as the more notable increasing trend of a steady creep rate with an increasing stress level, reflected by the larger slope and the intercept in the fitting relations. The main shear pattern and the combination of the shear and splitting failures are separately shown by the dry and saturated quartz sandstone. For the granite, both compression and extension exist in the creep deformation, and the failure may first occur in the prominent deformation area with a cracking noise. The AE hits present a similar time-dependent behavior to the strain of rock, and the attenuation trend happens in both the AE amplitude and energy before the rock enters the unsteady phase. The incomplete specimen of granite exhibits a lower strength and a larger deformation, owing to the more remarkable damage accumulation reflected by the spatial distribution of the AE event points.

Automated summary

The time-dependent mechanical properties of brittle rock are crucial for the stability of deep rock engineering, especially during excavation. This study conducted a uniaxial creep test with real-time DIC and AE technologies to investigate the behavior of quartz sandstone and granite. The results showed that the lateral strain and lateral ductility of quartz sandstone were sensitive to stress levels, while the saturated quartz sandstone exhibited bearing capacity before volumetric dilation. The moisture softening effect led to a nearly constant Poisson's ratio and a steady creep rate. For granite, both compression and extension occurred, and failure mainly occurred in prominent deformation areas. The AE hits showed a similar time-dependent behavior to the strain of rock, and attenuation occurred before the unsteady phase.