Change law of volume strain on gas filled coal under low frequency

To study the influence of low-frequency disturbance load on volume strain of gas-filled coal, the equation for change of volume strain of coal under porous pressure of coal, absorption strength and decreasing vibration stress is established. Then the rules depicted by the above equation are verified by changes of uniaxial compressive strength of samples which are vibrated for 1, 2, 3, 4, 5 hours under the action of frequency of 10, 20, 30 hz. It is found that under the constant vibrating frequency, with the increase of he vibrating time, the uniaxial compressive strength of samples gradually decreases, and the calculated strain increases. Under the constant vibrating time, with the decrease of the vibrating frequency, the uniaxial compressive strength of samples gradually increases, and the calculated strain decreases. The analysis shows that the vibration makes coal porosity increases, then the strain becomes larger, so the uniaxial compressive strength declines. Under the same vibrating time, when the frequency increases, the uniaxial compressive strength declines, the porosity increases, and the strain also becomes larger. However, under the same frequency, when the vibrating time gets shorter, the uniaxial compressive strength becomes greater, the porosity gets smaller, and the strain also becomes smaller. Whatever the value of the frequency gets, the uniaxial compressive strength decreases with the increasing time, which indicates that the porosity and the strain both increase with the increasing time. The variation of strain reflected by the compressive strength is the same as that of the calculated strain. The calculated values satisfactorily reveal influence of different frequencices and time ranges on strain changes under low frequency.