开采保护层是降低被保护层瓦斯含量和消除煤与瓦斯突出危险性最有效的区域性措施，目前关于保护层开采技术的研究工作较多，也取得了许多研究成果，但上保护层开采时，下伏煤岩体应力和变形特征较为复杂。随着采深的增加，采矿环境不断恶化，使得现有理论和技术滞后于实际需求，且上保护层开采时，采场下伏煤体间距不同，应力加卸载路径不同，引起煤体的变形状态和解吸瓦斯的运移方式不同，进而直接或者间接影响到瓦斯抽采措施的选择。鉴于此，本文通过理论分析、力学试验、渗流实验、数值计算和现场试验等方式，系统探究了上保护层开采对采场下伏不同距离处被保护层煤体力学、变形和渗流特征的影响，并成功指导了现场瓦斯抽采工作，为相似条件矿井被保护层卸压瓦斯抽采工作提供了参考。论文主要研究内容及成果如下：

（1）通过理论分析的方式得到了采场下伏不同间距煤岩体垂直应力变化量与水平应力变化量的分布曲线。发现保护层开采期间，下被保护层煤体出现了应力集中和应力卸载，且不同层间距应力表现出明显的差异。当层间距较小时，下被保护层煤体应力集中程度较大，卸荷时应力值接近煤体破坏的极限值，而随着层间距的增大，下被保护层煤体应力集中程度不断降低，卸荷时煤体的应力接近原始应力。据此设计了下被保护层煤体三轴加卸载试验应力路径。

（2）借助岩石三轴多场耦合试验系统开展了设计应力路径下的加卸载力学试验，结果表明：随着起始卸荷点偏应力的增大，卸荷过程中煤样的整体变形由体积压缩状态向体积扩容状态转变。且加载阶段的AE信号变化特征与常规三轴试验相似，而卸载期间，AE信号变化特征则与起始卸荷点偏应力大小相关。同时对卸荷期间煤样的变形模量、泊松比和损伤因子等进行了分析，发现当起始卸荷点所处煤样的变形阶段不同时，各个参数表现出明显的差异，其中在塑性阶段开始卸荷时，煤样的变形和损伤程度最大，且最终破坏是由环向膨胀变形的积累所导致的，即距离保护层越近，下被保护层煤体的损伤变形越大，且以膨胀变形为主。

（3）开展了三种应力路径下煤体的渗流试验，结果表明：常规三轴压缩试验中煤样的渗透率随着轴向应变的增加，表现出先减小后增加最终趋于稳定的变化特征。煤样初始渗透率随着围压的增大而减小，说明高地应力可显著抑制煤层的透气性，是瓦斯抽采工作面临的一大阻碍。不同层间距下被保护层煤体卸荷后，渗透率随着围压的减小呈指数关系增大，其增大程度受起始卸荷点应力及变形状态影响。起始卸荷点偏应力越接近峰值强度时，煤样破坏时渗透率越大，增透效果越明显，说明保护层卸压开采期间，下伏被保护层煤体渗透率随着层间距的减小而增大，且近距离下被保护层煤体受保护层开采卸压增透的效果最好。

（4）借助FLAC^3D数值计算的方式研究了上保护层开采期间不同层间距下被保护层应力场及位移场的分布特征。发现保护层回采期间，围岩出现了应力的升高和降低的现象。随着保护层采面推进距离增长，下被保护层卸压范围增大，垂直应力和垂直位移以采空区中部为基准，呈对称形式分布。获得了上保护层开采期间，不同间距下被保护层煤体的应力集中系数、卸压系数、最大压缩位移量、最大膨胀位移量和最大膨胀变形率随层间距的变化特征。

（5）开展了保护层开采期间采空区内混合瓦斯来源构成及占比测试试验，发现采空区混合瓦斯构成以近距离下被保护层解吸瓦斯为主。根据保护层开采期间下被保护层应力、变形及渗透率的变化特征，结合采空区内混合瓦斯来源测试结果，优化设计了下被保护层卸压瓦斯拦截抽采钻孔的布置方式，并对瓦斯抽采效果进行了考察，发现卸压瓦斯抽采效果较好，实现了消除下被保护层突出危险性的目的。

The mining of the protective layer is the most effective regional measure to reduce the gas content of the protected layer and eliminate the risk of coal and gas outburst. Currently, there is a significant amount of research on protective layer mining techniques, which has resulted in many research achievements. However, when mining the upper protective layer, the stress and deformation characteristics of the underlying coal and rock body are relatively complex. With the increase in mining depth, the mining environment deteriorates continuously, leading to a lag between existing theories and technologies and actual needs. Additionally, when the upper protective layer is mined, the spacing between the coal body under the stope is different, and the path of stress loading and unloading is different. This causes different deformation states of the coal bodies and different migration modes of relief gas, directly or indirectly influencing the selection of gas extraction measures. In view of this, through theoretical analysis, mechanical test, seepage test, numerical calculation and field test, this paper systematically explored the influence of mining of the upper protective layer on the mechanical, deformation and seepage characteristics of the coal body of the protected layer at different distances under the stope. It has successfully guided the field gas extraction work, and provided a reference for the relief gas extraction work of the mine protected layer under similar conditions. The main research content and achievements of this paper are as follows:

(1) Through theoretical analysis, distribution curves of the vertical stress variation and horizontal stress variation in the underlying coal-rock mass at different interlayer distances were obtained. It is found that during the mining of the protective layer, the underlying protected coal seam exhibited stress concentration and stress unloading, and significant differences in stress are observed at different interlayer spacing. When the interlayer spacing is small, the stress concentration in the underlying protected coal seam is significant, and the stress values during unloading approached the ultimate limit of coal failure. However, as the interlayer spacing increases, the stress concentration degree of the coal body in the lower protected layer decreases continuously, and the stress of the coal body during unloading is close to the original stress. Based on this, a stress path for the triaxial loading-unloading test was designed for the underlying protected coal seam.

(2) The loading-unloading mechanical tests under the designed stress path were carried out by means of the rock triaxial multi-field coupling test system. The results show that with the increase of the deviatoric stress at the initial unloading point, the overall deformation of the coal sample during the unloading process changes from the volumetric compression state to volumetric expansion state, and the variation characteristics of AE signals at the loading stage are similar to those of conventional triaxial tests. However, during unloading, the variation characteristics of AE signal are related to the deviatoric stress at the initial unloading point. Furthermore, the deformation modulus, Poisson's ratio, and damage factor of the coal sample during unloading were analyzed. It is found that when the deformation stage of the coal sample at the initial unloading point is different, various parameters show significant differences. In particular, when unloading start during the plastic stage, the coal sample exhibits the largest deformation and damage, and the ultimate failure is caused by the accumulation of radial expansion deformation. This indicates that the closer the distance to the protective layer, the greater the damage and deformation in the underlying protected coal seam, with expansion deformation being the dominant factor.

(3) Three types of seepage tests were conducted on coal samples along different stress paths. The results indicate that the permeability of coal samples in conventional triaxial compression tests exhibits a characteristic pattern of initially decreasing, then increasing, and ultimately stabilizing with the increase of axial strain. The initial permeability of coal samples decreases with the increase of confining pressure, indicating that high ground stress significantly inhibits the permeability of coal seams, posing a major obstacle to gas extraction operations. After unloading the coal body of the protected layer at different interlayer spacing, the permeability increases exponentially with the decrease of confining pressure, and the degree of increase is influenced by the initial unloading stress and deformation state. When the initial unloading bias stress approaches the peak strength, the permeability of coal samples at the point of failure becomes greater, and the permeability enhancement effect becomes more pronounced. This suggests that the permeability of the coal body of the underlying protected layer increases with the decrease of interlayer spacing during the unloading mining of the protective layer, and the pressure relief and permeability enhancement effect of the coal body of the near protected layer is the best.

(4) By means of FLAC^3D numerical calculation, the distribution characteristics of stress field and displacement field of the protected layer under different interlayer spacing during mining of the upper protective layer were studied. It is found that the stress of surrounding rock increases and decreases during the mining of protective layer. As the advancing distance of the protective layer increases, the range of unloading in the underlying protected layer increases. Vertical stress and vertical displacement are symmetrically distributed based on the central part of the goaf. The study obtained the variation characteristics of stress concentration coefficient, pressure relief coefficient, maximum compression displacement, maximum expansion displacement and maximum expansion deformation rate of the coal body in the lower protected layer with interlayer spacing during the mining of the upper protective layer.

(5) Tests were conducted to analyze the composition and proportion of mixed gases in the goaf during the mining of the protective layer, revealing that the main source of mixed gas in the goaf was desorbed gas from the lower protected coal seam at close range. Based on the variations in stress, deformation, and permeability of the underlying protected layer during the mining of the protective layer, and considering the test results of mixed gas sources in the goaf, the layout of relief gas intercepting and extracting drilling holes in the lower protected layer was optimized. The effect of gas extraction was investigated, and it was found that relief gas had better extraction effect, and the purpose of eliminating the outburst risk of the lower protected layer was realized.