Abstract
The impact of high temperatures on rocks is a topic of growing importance in geotechnical engineering due to its relevance to applications such as underground nuclear fuel storage, geothermal energy resource exploration and underground coal gasification. This paper presents results from tests performed on samples of sandstone treated to a range of temperatures between 20 and 1000°C. Sandstone samples obtained from underground coal gasification trial sites in Poland were selected for the tests. Multistage triaxial tests were used to determine the mechanical properties of the samples. X-ray diffraction and thermal analyses were performed to investigate the changes in physical and chemical properties of the samples under increasing temperature. Micro-computed tomography analyses were carried out on selected samples in order to show the microstructural changes that take place as a result of the heating process. Three-dimensional characterisation of sample porosity and pore-size distribution was performed to obtain a quantitative comparison between samples subjected to different temperature treatments. The relationship between microstructure and macro-mechanical characteristics of sandstone at high temperatures is discussed. The results illustrate that the mechanical properties of sandstone are closely related to alterations of microstructure that result from increased temperatures.
Highlights
The effect of high temperature on the thermo-mechanical response of rocks is important for several engineering applications, including underground nuclear waste storage, geothermal energy resource exploration, and underground coal gasification (UCG)
Multistage triaxial tests were used to determine the mechanical properties of the samples
The combined action of thermal evaporation and axial compression increases the density of the rock and its ability to resist deformation
Summary
The effect of high temperature on the thermo-mechanical response of rocks is important for several engineering applications, including underground nuclear waste storage, geothermal energy resource exploration, and underground coal gasification (UCG). The deformation mechanisms and failure criteria of different types of rocks at high temperatures has been studied by various researchers (Stesky et al 1974; Heuze 1983; Rao et al 2007; Wan et al 2009; Zhang et al 2009; Chen et al 2012; Ranjith et al 2012; Brotóns et al 2013; Wu et al 2013; Liu et al 2013; Zhang et al 2014) and it has generally been shown that high temperature has a significant effect on the mechanical properties of rocks. The rocks have been noted to respond in a brittle manner up to temperatures between 400-600 °C, and be more ductile for higher temperatures
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