The Mechanical Properties of Mudstone at High Temperatures: an Experimental Study

Abstract

Temperature is one of the main factors affecting the mechanical properties of rocks (Wang 1995). Rock mass involved in projects such as nuclear waste disposal, geothermal energy generation, and underground development in large cities is generally under high temperature conditions. Engineers need to know the rock’s mechanical parameters for excavation of underground rocks, design of supports, and for stability analysis of the surrounding rock. Therefore, the strength of the rock and its deformation behavior at high temperatures need to be understood (Wai et al. 1982; Al-Shayea et al. 2000). Since the 1970s, many researchers have investigated the effects of temperature on the mechanical properties of rocks (Yin et al. 2012a, b; Heuze 1983; Lau et al. 1995). Chen et al. (2012) measured the peak stress, peak strain, and elastic modulus of granite subjected to thermal treatment from 20 to 1,000 C. They found that the peak stress and elastic modulus of heated granite decreased as the heating temperature increased, while the peak strain increased. Xu et al. (2008) studied the mechanical characteristics of granite under the action of temperatures ranging from room temperature to 1,200 C and found that mechanical characteristics did not show obvious variations below 800 C; strength decreased suddenly above 800 C and bearing capacity was almost lost at 1,200 C. Dwivedi et al. (2008) reviewed the thermo-mechanical properties of granites from India and other locations. Through a series of physical and mechanical tests on salt rock at different temperatures (20–240 C), Liang et al. (2006) found that the ultrasonic velocity of the samples declined with rising temperature, while the uniaxial compressive strength and axial strain increased, whereas the tangent modulus had an opposite trend. Ferrero and Marini (2001) applied microscopic analysis to study crack densities in limestone and marble samples at temperatures up to 600 C. They found a correlation between the increase in open porosity due to new fractures and the crack density for both rocks. Zhao et al. (2012) studied the thermal deformation and failure mode of large-size granite specimens at high temperatures and pressures, and obtained the behavior of the thermodynamic parameters of the specimens, such as Young’s modulus, for various temperatures. Other studies (Zhang and Mao 2009; Mao et al. 2009; Luo and Wang 2011; Wu et al. 2005) concluded that the strength of most rocks decreased with increasing temperatures and that the drop in strength depended on the rock type. Although much knowledge has been gained through theoretical and experimental studies of granite, salt rock, and sandstone, few experimental studies on the mechanical properties of coal measures mudstone at real-time have been carried out because of limitations due to experimental L. Zhang Civil Engineering Department, Xuzhou Institute of Technology, Xuzhou 221008, Jiangsu, China