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| MECHANICAL PROPERTIES AND ULTRASONIC TIME-FREQUENCY CHARACTERISTICS OF THERMALLY DAMAGED SANDSTONE |
| WANG Peng1，XU Jinyu1，2，LIU Shi1，LIU Shaohe1 |
(1. Department of Airfield and Building Engineering，Air Force Engineering University，Xi′an，Shaanxi 710038，China；
2. College of Mechanics and Civil Architecture，Northwest Polytechnic University，Xi′an，Shaanxi 710072，China) |
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Abstract 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.
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Received: 28 April 2014
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2014, Vol. 33 
