Study on progressive damage failure characteristics and mechanism of high stress coal pillar under low frequency dynamic disturbance

When the mining face passes through the coal pillar, the problem of advanced dynamic instability of the coal pillar is often encountered. In order to explore the influence mechanism of mining disturbance on the dynamic instability of coal pillar, the dynamic compression test of high stress coal pillar under low frequency disturbance load was carried out. The results are as follows: There is a stress threshold value for the failure of coal samples under high stress (80% of the unilateral constrained compressive strength(UCCS)), and the threshold value is 15%UCCS. The number of disturbance load cycles before the failure of high stress coal samples crossing the stress threshold value group decreases exponentially with the increase of amplitude, and the increase of amplitude will significantly deteriorate the bearing capacity of coal samples. The irreversible strain, dissipated energy, secant modulus and damping ratio of coal samples crossing the stress threshold value show a three-stage evolution law in the process of disturbance load. In addition, with the increase of amplitude, the cumulative dissipated energy in the process of coal sample disturbance increases linearly, the maximum value is 0.242 kJ/m³, the mean value of secant modulus decreases linearly, and the minimum value is 1.101 GPa, while the mean value of damping ratio increases exponentially, and the maximum damping ratio is 1.593, that is, the increase of amplitude makes the internal deterioration of coal sample more serious. The large increase of AE energy in the initial stage of coal sample disturbance load can be used as an advanced criterion to judge whether the coal sample is damaged under the disturbance load, and the second surge of cumulative ring count can be used as the precursor information of coal sample damage beyond the threshold value. With the increase of amplitude, the b value of AE in the whole process of coal sample disturbance decreases linearly, and the minimum value is 1.369, that is, the larger the amplitude, the more sudden and severe the damage of coal sample. With the increase of amplitude, the fracture mode of coal samples crossing the stress threshold gradually changes from shear fracture to tensile or mixed fracture. The research can provide reference for the control of mining strength and the design of filling and reinforcing coal pillar when the re-mining working face passes through the coal pillar in the failure area of small kiln.