The practical application of the rock cavern storage of liquefied fuels (such as natural gas, liquid hydrogen or dimethyl ether) requires stability analysis of the cavern in question with regard to thermal stress, and an understanding of thermophysical properties and mechanical properties of rock mass is essential for such analysis.
In our research, a linear expansion strain measurement test up to —170°C was first conducted using Kimachi sandstone (24.0% porosity) to study the relationship between the freezing of pore water and its expansion strain. Then a uniaxial compression test and indirect tensile test were conducted with wet sandstone cooled down below freezing point to ultralow temperatures to review the influence of the formation of pore ice on the strength of wet sandstone. The following findings were obtained.
When Kimachi sandstone is cooled down, frost swelling occurs twice, and therefore the linear expansion coefficient fluctuates over range of temperatures between 0 to —70°C. This may be because pores of two different sizes exist in Kimachi sandstone and the freezing temperature of the pore water differs depending on the pore size. The compressive strength and indirect tensile strength of the wet sandstone increase with the decrease in the specimen temperature. Two causes of this phenomenon may be identified. One is that an increase in pore ice that shares the load is the main cause of the phenomenon in temperatures down to —50°C where freezing of the pore water is almost completed. The other is that an increase in strength by volumetric shrinkage of the rock forming minerals and pore ice is the main cause in temperatures below —50°C.
