Study On The Thermal Expansion Characteristics Of Rock Based On Micromechanics

In some related fields such as the exploitation of geothermal resources, the gasification and liquefaction of underground coals, the storage of oil and disposal of nuclear waste, the effect of temperature on the mechanical properties of rock cannot be ignored. For example, in the process of disposal of nuclear waste deeply, radioactive nuclear waste release a lot of heat, which makes the surrounding rocks to heat up. The rocks that have lager thermal expansion are compressed. And the rocks that have smaller thermal expansion are stretched. Therefore, they generate thermal stress by restraint to each other. The coefficient of thermal expansion(CTE) which represents the extent of thermal expansion for materials is closely related to field of thermal stress and strain in the heating rock. So the determination of CTE is needed.The main contents of this article are the following:Firstly, based on micromechanics the CTE is calculated, which can predict the CTE of rocks constituted by a variety of minerals.Secondly, Through the X-ray diffraction, NMR, uniaxial compression, ultrasonic testing and measurement of CTE, we have got the disciplines of mechanical parameters with temperature. Then we discussed the effect of these mechanical parameters on the thermal expansion coefficients. Finally, theoretical values and the measured values are compared.The study found that:(1) As for the effect of porosity on the CTE, the porosity measured in the temperature range of 25 ℃～600 ℃ is stable, so its effect on the CTE can be ignored. The Young’s modulus, Poisson’s ratio, peak stress and strain for slate show a certain regularity with the increasing temperature.(2)The CTEs of all kinds rocks mutate in about 600℃,which is related to the transformation of quartz phase. There are two different structures of α and β for quartz at 573 ℃, which makes its volume to produce a discontinuous increase.Therefore the CTE mutate.(3) Theoretical analysis shows that the effect of bulk modulus on CTE is decided by the relationship between bulk modulus and CTE of the main minerals. In the temperature range of 25 ℃～ 600 ℃, the effect caused by the bulk modulus is only 2% to 4%.So the bulk modulus’ effect can be ignored. There are some deviations in the comparison between theoretical and the measured values.