ABSTRACT

With increasing demand for LPG and LNG, more storage facilities are required in Korea. Due to the recent safety concerns and land shortage, storage facilities tend to be located in underground. For the construction of underground storage facilities for low temperature materials, mechanical and thermal properties of rock mass should be understood. In this study, laboratory experiments for the measurement of the mechanical properties such as UCS(Uniaxial compressive strength), tensile strength, fracture toughness etc. and thermal Properties such as specifie heat, thermal conductivity, and thermal expansion coefficient of rocks were performed In the temperature range of -160° to 40°. Experiment results show that UCS, tensile strength, fracture toughness increased with decreasing temperature, but Poisson's ratio, specific heat and the thermal expansion coefficient decreased with decreasing temperature. Elastic modulus and thermal conductivity changed little with decreasing temperature. These changes showed more clear tendency in wet specimens than dry ones. The results of this study can be utilized for the evaluation of thermal propagation in rock mass and the thermo-mechanical stability of underground facilities at low temperatures.

INTRODUCTION

The demand for LPG and LNG is increasing rapidly, and there are plans to build new liquefied gas storage facilities In Korea. For the construction of underground storage for low temperature materials such as frozen foods, LPG and LNG, thermal effects on structural stability underground should be considered. For solving this problem, besides the thermal and mechanical properties of rock under low temperature must be understood.

Thermal and mechanical properties of rocks under low temperature have been studied by some researchers. Aoki et al. (1989), Inada (1984), Ahn et al. (1997), Park (1999) performed the laboratory test for uniaxial compressive strength, tensile strength with decreasing temperature. Although there are some differences between their results, they showed that uniaxial compressive strength, tensile strength increased as the temperature decreased. Also these properties vary 0;' rock type, porosity, and the relative proportions of ice and unfrozen water.

For fracture toughness test, Ishizuka et al. (1984), jung et al. (2000) reported that fracture toughness, like the tensile strength, increased with decreasing temperature, and more clear for wet specimens.

Mellor (1970), Lindblom (1977), and Kuriyagawa et al. (I 980) showed that for wet specimens, the linear thermal expansion coefficient seems to decrease with decreasing temperature. Mellor evaluated the mean linear contraction (expansion) coefficient of rock specimens between -10°C and - 100°C and -90°C and -160°C to 4.13 × 10−6/°C and 3.52 × 10−6/°C, respectively. Lindblom (1977) evaluated the linear thermal expansion coefficient between shorter temperature intervals, which resulted in a coefficient closer to the differential coefficient at present temperature. The decreasing coefficient with decreasing temperature was also be studied by Aoki et al. (1989). For air-dry granite, Mellor reported that the coefficient was almost constant at about 4.8 × 10-6 /°C in the temperature range 0°C to -112°C. This correlates well with tests done by Kuriyagawa (1980).

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