Effect of loading frequencies on the dynamic properties of thermally treated rock samples

摘要

Temperature is one of several variables that can adversely impact the dynamic behavior of rocks by altering their geo-mechanical behavior. This study highlights the role of temperature changes on the measurement of resonance frequency (Fr) and quality factor (Q) parameters of selected rocks under different ranges of loading frequency. The samples for this study were collected in the eastern part of the Salt Range, Pakistan, focusing on sandstone formations. The samples were brought to the laboratory and NX size core samples were prepared. These samples were then heated up to 200°C with a gradual increment of 50°C, without causing any observable thermal shock. The cores were then air cooled and tested using Resonance Frequency meter equipment in accordance with the ASTM C-215 standard procedure at an applied loading frequency of 7 to 16 KHz. In this study resonance frequency (Fr), Quality factor (Q) and attenuation rate (α) values of thermally treated rock cores were determined using nondestructive testing under variety of applied loading frequencies. The results suggest that resonance frequency (Fr) of the samples initially increases up to a certain value, and then, starts decreasing, likely because of the healing and widening of thermally-induced micro-fissures, respectively. Similarly, Quality factor (Q) values and attenuation rate (α) exhibited significant variations in soundness and vibration energy absorption characteristics in the cores subjected to heating and cooling cycles. Overall, the results of these tests suggests that the strength of these sandstone cores decreased as the temperatures increased. Such studies could play a significant role in understanding the dynamic and mechanical response of host rocks in the vicinity of radioactive repositories, magmatic intrusions, hot springs, and geysers. It could also help to understand the structural un-sustainability issues in designing nuclear waste disposal sites, foundation of nuclear power plant projects and hazardous landfills etc.