Abstract

Due to differences in the properties of coal and gangue, gangue-containing coal often exhibits complex damage characteristics, which has become a key factor limiting the recovery rate in top coal caving. In order to improve the efficiency of top coal caving, it is necessary to recognize the failure mechanism of gangue-containing coal, especially the stress drop mode and the residual bearing capacity. In this paper, the post-peak mechanical properties of gangue-containing coal samples were investigated. With the aid of the PFC^2D software, a model of gangue distribution in different layers of gangue-containing coal samples was established by changing the bonding properties of the balls in different layers, and triaxial numerical simulation experiments were carried out under different confining pressures. According to the Mohr–Coulomb failure criterion, a post-peak stress–strain model based on equivalent plastic strain was proposed for gangue-containing coal. The results show that the theoretical values are in good agreement with the numerical simulation values. The strength is mainly affected by the cohesive force during the first stress drop, and the effect of the internal friction angle on the strength cannot be neglected during the second stress drop. Furthermore, the brittleness characteristics of gangue-containing coal are studied. It is found that the brittleness drops rapidly when the confining pressure rises from 5 to 10 MPa, and the position of gangue has a significant impact on the softening coefficient. Finally, the quantitative relationship between the brittleness and the burst proneness was established from the perspective of energy, and the brittleness was partitioned according to the burst proneness. The research findings are beneficial for improving the recovery rate and identifying the burst proneness of coal seams to ensure safe and efficient production.

Highlights

• The first and second stress drops are affected by the cohesion C and the internal friction angle, respectively.

• The position of gangue has a significant impact on the softening coefficient.

• The quantitative relationship between the brittleness and the burst proneness was established from the perspective of energy.

中文翻译：

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含石煤样品的应变软化和脆性特性

摘要

由于煤和煤ue石性质的差异，含煤gang石的煤常常表现出复杂的破坏特征，这已成为限制放顶煤采收率的关键因素。为了提高放顶煤的效率，有必要认识到含石煤的破坏机理，尤其是应力下降模式和残余承载力。本文研究了含石煤样品的峰后力学性能。借助PFC ^2D在软件中，通过改变球在不同层中的结合特性，建立了含煤gang石样品在不同层中的脉石分布模型，并在不同围压下进行了三轴数值模拟实验。根据Mohr-Coulomb破坏准则，提出了基于等效塑性应变的含石煤峰值后应力-应变模型。结果表明，理论值与数值模拟值吻合良好。强度主要受到第一应力下降期间的内聚力的影响，并且在第二应力下降期间不能忽略内摩擦角对强度的影响。此外，研究了含石煤的脆性特性。结果发现，当围压从5 MPa增加到10 MPa时，脆性迅速下降，脉石的位置对软化系数有很大影响。最后，从能量的角度建立了脆性与爆裂倾向性之间的定量关系，并根据爆裂倾向性对脆性进行了划分。该研究结果对于提高采收率和确定煤层的破裂倾向性以确保安全和有效的生产是有益的。脆性根据爆裂倾向性进行分配。该研究结果对于提高采收率和确定煤层的破裂倾向性以确保安全和有效的生产是有益的。脆性根据爆裂倾向性进行分配。该研究结果对于提高采收率和确定煤层的破裂倾向性以确保安全和有效的生产是有益的。

强调

• 第一和第二应力降分别受内聚力C和内摩擦角的影响。

• 脉石的位置对软化系数有重要影响。

• 从能量的角度建立了脆性和爆裂倾向之间的定量关系。