Gas porosity formula under low frequency vibration and its testing analysis

To study the influence of low-frequency disturbance load on gas porosity,the authors developed a porosity formula under coal porosity pressure, absorption strength and decreasing vibration stress. The authors adopted the change law of porosity and uniaxial compressive strength,and tested the uniaxial compressive strength changes of a sample under different frequencies and different vibrating time models. The test reveals that uniaxial compressive strength decreases and porosity increases when vibrating time extends under the low frequency and same frequency. When frequency decreases,uniaxial compressive strength increases and porosity declines. At the frequencies of 30 Hz and 20 Hz,the D-value of uniaxial compressive strength porosity is smaller than that at the frequencies of 20 Hz and 10 Hz. The test also demonstrates that vibration increases porosity and then decreases uniaxial compressive strength. Moreover,at the increasing frequencies of 10 Hz,20 Hz and 30 Hz,porosity gradually increases and uniaxial compres- sive strength decreases respectively. The calculated porosity reflects the variation of uniaxial compressive strength un- der vibration. The authors compared the relationship between calculation porosity and uniaxial compressive strength, and then obtained the class exponential change law of the former. The formula best reveals the different frequencies and time ranges imposed on the porosity changes under low frequency.