Effects of Wetting and Cyclic Wetting–Drying on Tensile Strength of Sandstone with a Low Clay Mineral Content

Sandstones are encountered in many underground excavations and mines, and in addition, because of their abundance, they are commonly used as building stone and aggregate material for dams, railway or airport foundations, and other infrastructures (Shakoor and Barefield 2009). Therefore, understanding the mechanical behavior of sandstones and how they are affected by environmental factors such as saturation or temperature is clearly important. A number of experimental studies have shown that various sandstones could suffer a significant loss of uniaxial and confined compressive strength upon saturation (Colback and Wild 1965; Burshtein 1969; Hawkins and McConnell 1992; Vasarhelyi 2003; Lin et al. 2005; Li et al. 2005; Aydan 2012; Duda and Renner 2013; Wasantha and Ranjith 2014). For clay-bearing rocks, the saturation-induced reductions in strength and stiffness can be up to 80 % (Cherblanc et al. 2016; Vergara and Triantafyllidis 2016). In contrast, Reviron et al. (2009) did not observe any notable effect of water on the strength of sandstones composed almost exclusively of quartz with the absence of clay minerals. Hawkins and McConnell (1992) showed that the sudden decrease in strength commonly occurred at a moisture content well below saturation. Wong and Jong (2014) found that the tensile strength of an artificially molded gypsum rock called Hydrocal B-11 dropped to nearly half of its dry value after being soaked in water for one week; the tensile strength continued to fall slightly after the samples were immersed in water for three and ten weeks. However, how the tensile strength of sandstone changes when it has been soaked in water for a long period is still not well understood. In addition to long-term wetting, dams and infrastructure foundations may also be subjected to cyclic wetting– drying during their construction and operation, owing to rain or changes in groundwater levels. Cyclic wetting– drying is another acknowledged yet poorly understood rock weathering process. The physical and mechanical properties of sandstone samples deteriorate to different degrees after cyclic wetting–drying treatments (Table 1). Hale and Shakoor (2003) reported no observable effect on the uniaxial compressive strength of sandstone even after 50 wetting–drying cycles. However, a recent study by Deng et al. (2012) showed that cyclic wetting–drying can significantly decrease the mechanical properties of sandstone. In the studies cited, the samples were tested under wet condition after the cyclic wetting–drying treatments, but their properties were not systematically investigated under dry condition after the samples experiencing wetting–drying cycles. Therefore, the effect of cyclic wetting–drying on sandstone’s tensile strength still remains incompletely understood. This experimental study was focused on the following two issues: (1) the effect of immersion time on sandstone deterioration along with the recovery of tensile strength from saturated to dry conditions and (2) the effect of cyclic wetting–drying on sandstone tensile strength. & Zhihong Zhao zhzhao@tsinghua.edu.cn