Abstract
The natural fractures in rock mass are susceptible to damage evolution when subjecting to repeated freeze-thaw (F-T) weathering in cold regions, which can lead to the instability of rock engineering and even occurrence of geological hazards. Knowledge of how natural fracture impacts the overall fracture evolution of freeze-thawed rock is important to predict the stability of rock structure. In this work, we reported uniaxial experimental measurements of the changes in strength, deformation, acoustic emission (AE) pattern, and Felicity effect during increasing amplitude stress-cycling conditions on granite. The results show that the change of fracture aperture is related to the fracture openness and filling characteristics, open-type fracture is sensitive to F-T treatment, and its aperture increases faster than the close-type and fill-type fracture. In addition, strength decreases, and the damping characteristics first decrease and then increase with increasing natural fracture volume. AE activities also present different responses during sample deformation. The proportion of AE signals having low-frequency characteristics increases with increasing natural fracture volume, and the shear sliding along natural fracture results in the surge of AE activities. Moreover, the Felicity effect indicates that the Felicity ratio presents a fluctuation decreasing trend, and the preexisting fractures alter the stress memory characteristics of rock. It is suggested that the changes of the geomechanical and AE pattern are the interactions between the natural fracture and the newly stimulated fracture. The testing results are expected to improve the understanding of the influence of natural fractures on rock fracture evolution and can be helpful to predict the stability of rock structures and rock mass in cold regions.
Highlights
Freeze-thaw (F-T) weathering frequently occurs in cold regions, and it leads to the deterioration of rock geomechanical properties, severely impacts the stability of rock engineering and even inducing geological hazards
To investigate the impacts of the preexisting natural fracture on the mechanical and acoustic emission characteristics of hard rock samples after F-T treatment, cyclic loading test combined with in situ AE monitoring technique was carried out on naturally fractured granite samples cored from an open pit mine slope located in the Hejing country, Xinjiang province
Some main conclusions can be summarized from the present study: (1) During cyclic F-T treatment, frost heaving pressure generates and acts on the natural fractures, and the fracture aperture changes with increasing F-T cycle
Summary
Freeze-thaw (F-T) weathering frequently occurs in cold regions, and it leads to the deterioration of rock geomechanical properties, severely impacts the stability of rock engineering and even inducing geological hazards. For rock mass containing structure planes, often named as natural fracture, the water migration and water-ice phase transformation in the preexisting fractures are stronger than the intact rock. Under F-T conditions, a 9% volumetric expansion occurs when water turns to ice [1,2,3,4,5], and frost heaving pressure would produce within the natural fractures. The frost heaving pressure further drives the propagation of natural fractures, resulting in the increment of fracture aperture and length, and deteriorates the rock structure. The existing of natural fractures in rock structure is much more dangerous than in the normal thermoneutral condition. It is of great importance to investigate the mechanical properties of naturally fractured rock in cold regions
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