高温影响下花岗岩孔径分布的分形结构及模型

Fractal structure and model of pore size distribution of granite under high temperatures

温度是影响岩石物理性质的重要因素，为了探究温度对岩石孔径分布的影响规律，利用压汞法测试25℃～1200℃高温热处理后花岗岩样品的孔隙特征，并研究了不同高温影响下岩石孔隙的分形结构和孔隙率演化模型。结果表明：（1）随着温度的升高，岩石孔隙率呈指数增加，500℃～800℃是岩石孔隙结构变化的阈值温度区间，500℃之前孔隙率增长较缓慢，增长幅度约50％，之后孔隙率大幅增加3～5倍；（2）温度升高所导致的岩石新孔隙以孔径1～10μm的中孔为主，低于500℃时中孔占15％左右，而后稳步上升，800℃时大幅增加至28．24％，1000℃以后又增至40％以上，体积增长了11．8倍，这将导致岩石防渗阻渗能力大大减弱；（3）各温度下岩石孔隙分布均具有良好的统计分形特性，孔隙分形维数在2．99～3．00范围，随温度升高，分形维数降低，且温度越高，降低幅度越大，表明孔隙均匀性增加；（4）基于理想Menger海绵的Friesen模型预测各孔径下累计孔隙率演化误差较大，而张季如和陶高梁模型对不同高温岩石孔径分布具有良好的预测精度。研究结果将为高放核废料深层地下存储、地热开发等高温岩石工程设计及施工提供科学依据。

Temperature is one of the important factors influencing the physical properties of rock. In order to obtain the effect of temperature on the pore size distribution in rock material, the mercury intrusion porosimetry was adopted to test the pore characteristics of granite samples after high temperature treatment of 25℃ - 1 200 ℃. The fractal structure and model of pore size distribution under different high temperatures were then studied. The results showed that the rock porosity increased exponentially with the rising heating temperature and 500℃ - 800 ℃was a threshold temperature interval. The porosity increased only 50% below 500℃ and about 3 to 5 times from 500 ℃ to 1 200 ℃. Most of the new pores and cracks induced by the high temperature are meso pores with the average diameter between 1 ~tm and 10 μm. The meso pores account for about 15% when the heat temperature is lower than 500℃, and then increases steadily and reaches 28.24% at 800℃, more than 40% over 1 000 ℃, and its volume increases by 11.8 times. The pore size distribution of rock under different temperatures exhibits a good statistical fractal feature with the pore fractal dimension between 2.99 and 3. With the rising of the temperature, the fractal dimension decreases more and more, which shows that the uniformity of pore distribution is raised. The model by ZHANG Jiru and TAO Gaoliang are proved better than the one of Friesen model based on ideal Menger sponge in predicting the rock porosity of different pore size.