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不同应变率下松软煤体动态压缩力学特征试验

Tests on dynamic compression mechanical properties of soft coal under different strain rates

  • 摘要: 深部冲击荷载扰动极易诱发松软煤层围岩失稳事故。为研究不同应变率下松软煤体动态力学特征,针对淮南矿区潘一矿11518工作面松软煤体,压制ø50×25 mm的圆柱形型煤试样,运用分离式霍普金森压杆试验系统,开展5组冲击速度下(0.30、0.35、0.40、0.45、0.50 MPa)煤体的动态压缩试验,获取煤体动态应力−应变曲线,计算破碎耗能及耗能密度,筛分不同粒径区间破碎煤体质量,分析煤体力学特征参数、能量耗散及破碎特征随应变率的变化规律,揭示煤体冲击破坏的应变率效应。结果表明:① 在试验应变率范围内,煤体初始压密阶段均不明显,且随应变率的增高,弹性变形阶段曲线斜率缓慢增大,屈服阶段有所增长,软化阶段应力降幅增大。② 煤体峰值应力、峰值应变、割线模量随应变率的增高均具有线性增大的变化特点,增幅分别为130.998%、111.335%、52.026%。③ 随应变率的增高,煤体破碎耗能及破碎耗能密度均呈指数增长,破碎耗能占比逐渐增大。④ 应变率越大,破坏后煤体小体积碎块越多,应变率由66.778 s−1变化到259.154 s−1过程中,碎块平均粒径由3.34 mm逐渐降低至2.49 mm,碎块分形维数由2.37缓慢增大到2.61,型煤与原煤(应变率为57.433~240.100 s−1)破碎特征随应变率变化趋势具有一致性。研究结果可为厘清松软煤体冲击动态力学响应过程、防控失稳灾害提供试验依据。

     

    Abstract: The disturbance of deep impact loading can easily induce the instability accident of surrounding rock in soft coal seam. In order to study the dynamic mechanical characteristics of soft coal under different strain rates, aiming at the soft coal of 11518 working face in Panyi Coal Mine of Huainan Mining Area, the cylindrical briquette samples of ø50 × 25 mm were pressed. The Split Hopkinson Pressure Bar (SHPB) equipment system was used to carry out the dynamic compression test of coal under five groups of impact velocities (0.30, 0.35, 0.40, 0.45, 0.50 MPa). The dynamic stress-strain curve of coal was obtained, the crushing energy consumption and energy consumption density were calculated, the quality of broken coal in different particle size ranges was screened, and the variation of mechanical characteristic parameters, energy dissipation and crushing characteristics of coal with strain rate were analyzed. The strain rate effect of coal impact failure was revealed. The results show that: ① In the range of strain rate in test, the initial compaction stage of coal is not obvious, and with the increase of strain rate, the slope of the curve in the elastic deformation stage increases slowly, the yield stage increases, and the drop of stress in the softening stage increases. ② The peak stress, peak strain and secant modulus of coal increase linearly with the increase of strain rate, with an increase of 130.998 %, 111.335 % and 52.026 %, respectively.③ With the increase of strain rate, the crushing energy consumption and crushing energy consumption density of coal increase exponentially, and the proportion of crushing energy consumption increases gradually. ④ The larger the strain rate, the more the small volume fragments of coal after failure. In the process of strain rate changing from 66.778 s−1 to 259.154 s−1, the average particle size of the fragments gradually decreased from 3.34 mm to 2.49 mm, and the fractal dimension of the fragments increased slowly from 2.37 to 2.61. The variation trend of crushing characteristics of briquette with strain rate is consistent with that of raw coal (strain rate 57.433 ~ 240.100 s−1). The research results can provide experimental basis for clarifying the dynamic mechanical response process of soft coal under impact loading and preventing and controlling instability disasters.

     

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