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层理煤岩浸水前后力学性质研究

Study on mechanical properties of coal before and after flooding considering bedding direction

  • 摘要: 层理弱面及煤岩遇水软化会导致煤岩力学性质降低,对煤矿地下水库稳定性、煤矿突透水事故防治等具有重要影响。为了研究层理及浸水对煤岩力学性质的综合影响,通过无损浸水试验与单轴压缩试验,并基于数字图像相关(Digital Image Correlation,DIC)技术,分析不同浸水条件下煤岩单轴压缩变形及破坏特性,获得了轴向平行和轴向垂直两种层理煤岩在天然状态、自然吸水以及强制吸水三种状态下的力学性质参数和表面应变场信息等。研究结果表明:煤岩的吸水特性呈现出明显的层理性差异,力学性质受到层理和浸水共同影响作用,具体如下:①毛细管作用导致轴向平行层理煤岩吸水能力强于轴向垂直层理煤岩,轴向平行层理煤岩的自然极限吸水率是轴向垂直层理煤岩的2.2倍;②煤岩的单轴抗压强度和弹性模量受层理影响为主,受浸水影响为辅,破坏模式与层理方向有关系,轴向垂直煤岩为剪切破坏,轴向平行煤岩为劈裂破坏,相同层理煤岩浸水前后破坏模式不变;③煤岩破坏是由均匀变形向非均匀变形转化的过程,浸水后煤岩会更早出现应变集中区,其压密阶段延长、弹性变形阶段缩短。研究结果有助于进一步理解轴向平行和轴向垂直两种层理煤岩浸水特性、力学性质及破裂演化规律,对地下水库预留煤柱保护、稳定性分析等相关工程实践具有一定的借鉴作用。

     

    Abstract: The weak bedding plane and the water-softening coal will lead to the decrease in mechanical properties, which has an important influence on the stability of underground reservoirs and the prevention and control of water inrush accidents in coal mine. To study the comprehensive influence of bedding and soaking on the mechanical properties of coal, the uniaxial compression deformation and failure characteristics of coal under different soaking conditions were analyzed through a non-destructive soaking test and uniaxial compression test and based on the Digital image correlation method (DIC). The mechanical property parameters and surface strain field information of axial parallel and vertical bedded coal samples in the natural state, natural water absorption and forced water absorption were obtained. The results shown that the water absorption characteristics of coal shown obvious stratification differences, and the mechanical properties were affected by the combined effects of stratification and soaking. The specific results were as follows, ① Capillary action led to stronger water adsorption in axial parallel-bedded coal than in axial vertical-bedded coal, and the natural limiting water absorption rate of axial parallel-bedded coal was 2.2 times higher than that of axial vertical-bedded coal. ② The uniaxial compressive strength and elastic modulus of coal were mainly affected by bedding and supplemented by soaking. The failure mode was related to the direction of bedding. The failure mode of axial vertical coal was shear failure, while that of axial parallel coal was split failure. ③ The coal failure was a process of transformation from uniform to non-uniform deformation. After water soaking, the coal appeared strain concentration area earlier, its compaction stage was prolonged, and the elastic deformation stage was shortened. The research results were helpful to further understand the water soaking characteristics, mechanical properties, and rupture evolution of axial parallel and vertical bedded coals, and can be used as a reference for the protection and stability analysis of reserved coal pillars in underground reservoirs.

     

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