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低频动力扰动下高应力煤柱渐进损伤破坏特征及机理研究

Progressive damage failure characteristics and mechanism of high-stress coal pillar under low-frequency dynamic disturbance

  • 摘要: 采掘工作面过煤柱时常常会遇到煤柱超前动力失稳问题。为探究开采扰动对煤柱动态失稳的影响机制, 开展了低频扰动荷载作用下高应力煤柱的动态压缩试验。结果表明: ①煤样在高应力(80%单向约束抗压强度(UCCS))状态下的破坏存在应力门槛值, 门槛值为15%UCCS, 越过应力门槛值的高应力煤样破坏前的扰动荷载周期数随幅值增加呈现指数型衰减的规律, 幅值的升高会显著劣化煤样的承载能力。②越过应力门槛值的煤样在扰动荷载作用过程中的不可逆应变、耗散能、割线模量和阻尼比均呈现3阶段演化规律; 此外, 随幅值的增加, 煤样扰动过程中累计耗散能线性增加, 最大值为241.932 kJ/m3, 割线模量均值线性减小, 最小值为1.101 GPa, 而阻尼比均值呈现指数增加的规律, 最大阻尼比为1.593, 即幅值的增加使煤样内部劣化得更加严重。③煤样扰动荷载施加的初期阶段声发射(AE)能量的大幅增加可作为判断煤样在扰动荷载作用下是否破坏的超前判据, 累计振铃计数第2次激增可以作为越过门槛值煤样破坏的前兆信息; 随着幅值的增加, 煤样扰动全过程声发射b值线性减小, 最小值为1.369, 即幅值越大, 煤样破坏得越突然、越剧烈。④随着幅值的增加, 越过应力门槛值煤样的破裂模式由剪切破裂为主逐渐过渡到以张拉或混合破裂为主。本研究可为小窑破坏区复采工作面过煤柱时采掘强度控制及充填加固煤柱设计提供参考。

     

    Abstract: When the mining face approaches the coal pillar, dynamic instability occurs in front coal pillar. To explore the influence mechanism of mining disturbance on dynamic instability of coal pillar, the dynamic compression test of high-stress coal pillar under low-frequency disturbance load was carried out. The results show 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% of UCCS. Subjecting to the stress over the threshold value, the number of disturbance load cycles before the failure of high-stress coal samples decreases exponentially with the increase of amplitude, and the increase of amplitude significantly deteriorates the bearing capacity of coal samples. Also, the irreversible strain, dissipated energy, secant modulus and damping ratio of coal samples show a three-stage evolution law under disturbance load. In addition, with the increase of amplitude, the cumulative dissipated energy in the process of coal sample disturbance increases linearly with the maximum value of 241.932 kJ/m3. The mean value of secant modulus decreases linearly with the minimum value of 1.101 GPa. However, the mean value of damping ratio increases exponentially with the maximum damping ratio of 1.593, indicating the increase of amplitude makes the internal deterioration of coal sample more serious. The large increase of AE energy in the initial disturbance loading stage of coal sample can be used as an advanced criterion to judge whether the coal sample is damaged, and the second surge of cumulative ring count can be used as the precursor information of coal damage beyond the threshold value. With the increase of amplitude, the b value of AE in the whole disturbance loading process on coal decreases linearly with the minimum value of 1.369. In other words, 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 when subjecting to stress beyond the threshold gradually changes from shear fracture to tensile or mixed fracture.

     

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