Abstract
The understanding of the weakening mechanism of tensile strength of rock subjected to cyclic wetting-drying is critical for rock engineering. Tensile strength tests were conducted on a total of 35 sandstone specimens with different wetting-drying cycles. The crack propagation process and acoustic emission characteristics of the tested samples were obtained through a high-speed camera and acoustic emission system. The results indicate that the tensile strength is observably reduced after cyclic wetting-drying, and the extent of the reduction is not only related to the number of wetting-drying cycle, but also closely related to the clay mineral content of the sample. In addition, as the cycles of wetting-drying increase, the effect of each single cycle on tensile strength get reduced until it becomes constant. Moreover, the crack initiation and penetration time is prolonged as the number of wetting-drying cycle increases, which indicates that cyclic wetting-drying weakens the rock stiffness and enhances the ductility of sandstone. Meanwhile, the acoustic emission characteristics of the tested samples further confirmed the ductile behaviour of the sandstone samples with increasing wetting-drying cycle. Furthermore, through the analysis of the microstructure and mineral composition of the samples with different wetting-drying cycles, it is concluded that the main weakening mechanisms of sandstones containing clay minerals are frictional reduction, chemical and corrosive deterioration.
Highlights
Many rocks in nature and rock engineering are subject to cyclic wetting-drying, such as rock in pumping reservoirs, coastlines, exposed slopes, etc. (Yang et al 2017; HanEffect of cyclic wetting–drying on tensile mechanical behavior and microstructure of clay-bearing...deterioration (Yilmaz 2010; Karakul and Ulusay 2013; Wong et al 2015; Momeni et al 2017; Wu et al 2018; Eang et al 2018).In addition to the mechanical behavior of rock under uniaxial and triaxial conditions, substantial research efforts have recently been focusing on the effects of water–rock interaction on the mechanical behavior under tensile conditions (Fu et al 2017; Huang et al 2010), especially under the state of cyclic wetting-drying
The results indicate that the tensile strength is observably reduced after cyclic wetting-drying, and the extent of the reduction is related to the number of wettingdrying cycle, and closely related to the clay mineral content of the sample
This paper mainly discussed the effect of cyclic wettingdrying on tensile mechanical behavior of sandstone through experiment
Summary
Many rocks in nature and rock engineering are subject to cyclic wetting-drying, such as rock in pumping reservoirs, coastlines, exposed slopes, etc. Through the experimental research on artificial gypsum, it is found that the tensile strength of wet gypsum is about 50% lower than that of dry gypsum, but the strength under different soaking duration is not much different, and it is found that the effect of water-rock interaction has a great influence on the development of crack (Wong and Jong 2014). For sandstone with a low clay mineral content, experimental result shows that the tensile strength is affected by the water state of the rock, but is probably not sensitive to the length of immersion, and that cyclic wetting-drying does not necessarily reduce the tensile strength permanently. Regarding sandstones containing clay minerals in particular, the effect of the number of wetting-drying cycles on the tensile mechanical behavior of the rock, and how the cyclic wetting-drying changes the microstructure of rock and affects the macroscopic mechanical properties, remain unclear. The mechanism of the influence of cyclic wetting-drying on rock mechanical behavior is discussed
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