Abstract
In this paper, shear displacement properties of rock fractures were studied, and the energy evolution process was analyzed before sliding instability under complex shear loading paths. The artificial prefabrication method was used to simulate the natural rock fractures, which are difficult to obtain in the natural environment. The prepeak tiered cyclic loading tests under constant normal loading were performed on six rock specimens with fractures by rock direct shear apparatus (RDS-200). To obtain the stress difference of adjacent cycles, the direct shear test was conducted on the other six rock specimens with fractures before the prepeak tiered cyclic shear loading test. The variation trend of residual shear displacement (RSD) and the similarity of loading and unloading curves before slip instability were obtained by analyses of prepeak tiered cyclic shear loading test data. Energy evolution laws of rock fractures were analyzed with the consideration of the hysteresis characteristics, according to the hysteresis effect of shear displacement behind shear stress. This paper provides guidance for the study on shear instability of rock fractures under complex loading paths.
Highlights
Rock fractures have a controlling function in the stability of the rock slope with a planar failure surface [1, 2]. e failure inside rock mass often occurs along the weak structural plane, and deformation and failure of rock projects are greatly affected by mechanical properties of the structural plane under the external loading [3,4,5,6,7,8]
To better understand the shear mechanical behavior, the information value (IV) and the fractal theory (FT) models are employed to determine the shear failure regions of rock joints under the low effective normal stress conditions [21]. e previous research has shown that, during the periodical change of the reservoir level and reciprocating motion of the train, rock masses are affected in the form of tiered cyclic loading, and the failure of rock fractures caused by tiered shear loading was different from that by the shear loading state at a constant rate [22]
Shear strength of the six rock fractures under prepeak tiered cyclic shear loading is lower than the average direct shear strength due to the continuous damage caused by the cyclic shear loading
Summary
Rock fractures have a controlling function in the stability of the rock slope with a planar failure surface [1, 2]. e failure inside rock mass often occurs along the weak structural plane, and deformation and failure of rock projects are greatly affected by mechanical properties of the structural plane under the external loading [3,4,5,6,7,8]. Tiered cyclic loading is a common form acting on rock mass, such as periodical change of the reservoir level and reciprocating motion of the train [12,13,14,15]. Kou et al [19] investigated in the laboratory the mechanical response of rock joints with multiscale triangular-shaped asperities, including primary and subordinate asperities, when subjected to prepeak cyclic shear loads and static constant normal loads (CNL). E previous research has shown that, during the periodical change of the reservoir level and reciprocating motion of the train, rock masses are affected in the form of tiered cyclic loading, and the failure of rock fractures caused by tiered shear loading was different from that by the shear loading state at a constant rate [22]. Compared with the shear test at the constant shear rate, the slip and dislocation caused by the prepeak tiered shear stress on the rock fracture are not obvious, because the prepeak tiered shear stress is smaller than the peak shear stress
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