热损伤砂岩力学与超声时频特性研究

MECHANICAL PROPERTIES AND ULTRASONIC TIME-FREQUENCY CHARACTERISTICS OF THERMALLY DAMAGED SANDSTONE

岩石经历高温作用后会产生不同程度的热损伤。通过单轴压缩试验,对经历25℃,100℃,200℃,400℃,600℃,800℃,1 000℃高温作用后的砂岩试样力学特性进行分析;通过超声纵波试验,基于小波变换方法,在时域和频域对其超声特性进行研究。提出频谱峰度(KFS)的概念,用以描述超声信号频率分布的杂乱/集中程度。研究发现:随着作用温度的升高,砂岩试样表面色调变暖,纵波波速显著降低,波形趋于紊乱,峰值应变增大,峰值应力、弹性模量变化呈现出非线性特征。在频域对超声信号进行分析发现,砂岩试样接收谱形心频率和频谱峰度随温度的变化呈非单调性,其与峰值应力、弹性模量的变化规律有较强的一致性。砂岩是一种典型的矿物胶结岩,矿物颗粒和胶结物在高温作用下产生不同变化,并对砂岩的各项特性产生不同影响。以宏观的声学力学特征变化探究不同等级高温作用后砂岩的热损伤,研究结果对高温环境岩石工程具有一定的指导意义。

Thermal damage of rock occurs after experience of high temperature of different levels. The mechanical properties of thermally damaged sandstone specimens experienced temperature treatments of different levels, including 25 ℃,100 ℃,200 ℃,400 ℃,600 ℃,800 ℃ and 1 000 ℃,were studied with the uniaxial compression tests. The ultrasonic characteristics in both the time and frequency domains according to wavelet transform were analyzed based on the data from the ultrasonic longitudinal wave testing. The kurtosis of frequency spectrum（KFS） was proposed to describe the degree of the clutter/concentration of the ultrasonic signal frequency distribution. It was found that with the temperature rising,the surface tone of sandstone specimen turned warmer, the longitudinal wave velocity was reduced significantly and the waveform tended to disorder. The peak strain increased. However,the peak stress and the elastic modulus varied nonlinearly. By the analysis of ultrasonic signals in frequency domain,the centroid frequency and the KFS of the receiving spectrum changed non-monotonic with the temperature,just as the relationship between the peak stress and the modulus of elasticity. The sandstone is a typical mineral cemented rock. The mineral grains and cements produce different changes and thus have different effects on the characteristics of the rock after the treatment of high temperature.