大倾角煤层是指煤层倾角为35°~55°的煤层，是国际采矿界公认的难采煤层。大倾角煤层广泛赋存于我国西部矿区和东部矿区深部，该类煤层的安全高效开采对促进我国区域经济协调发展具有重要支撑作用。在大倾角煤层开采过程中，受煤层倾角影响，底板的受载历程和变形破坏特征与近水平煤层开采时存在显著差异，造成底板稳定性控制难度大。因此，深入研究大倾角煤层底板变形破坏机理对促进该类煤层安全生产具有重要的理论和工程意义。本文采用相似模拟实验、数值计算和理论分析相结合的研究手段，对大倾角煤层走向长壁开采底板采动应力形成演化规律、非对称变形破坏演化机理进行分析与研究。结果表明：

(1) 大倾角煤层开采过程中，底板卸荷膨胀产生离层裂隙形成滑移体，并在自身重力下沿着滑移面滑出，冒落矸石沿工作面倾向下滑形成下部“填满”、中部“填实”、上部“部分悬空”的非均匀充填带。在冒落矸石非均匀充填带和倾向上侧煤体推挤载荷影响下，工作面倾向下部底板的破坏深度和裂隙长度均大于倾向上部。随着工作面推进距离的增加，底板垂直位移量和倾向上、下侧煤体的支承压力峰值均呈现出先增加后稳定的演化趋势。

(2) 受开采扰动作用，底板竖向切应力t_zx和t_zy增大，主应力方向发生偏转，形成新的采动应力传递路径，致使底板应力状态发生改变。工作面煤壁前方底板处于受压状态，易发生压剪破坏；而采空区底板处于受拉状态，易产生拉伸破坏。当工作面推进距离大于3倍工作面长度，底板主应力方向偏转规律和大小渐变特征逐渐趋于稳定，导致工作面煤壁前方支承压力峰值呈现出先升高，后稳定的演化趋势。

(3) 受煤层倾角影响，在工作面倾向剖面，底板应力传递路径呈非对称拱型分布特征。该应力包络拱内部，底板主应力降低，方向发生明显降低，并形成受拉区域；应力包络拱外部，工作面倾向上、下侧煤体覆岩载荷向应力偏转界线两侧底板传递。在工作面走向剖面，底板应力传递路径呈对称扁平拱形。随着煤层倾角的增加，应力包络拱拱高呈现减-增-减的演化趋势。受此影响，工作面倾向上侧煤体应力集中系数亦呈现增-减-增的演化趋势，而倾向下侧煤体则呈现减-增-减的演化趋势，应力偏转界线位置则逐渐向工作面倾向下部底板迁移。

(4) 采场底板形成倾斜“椭球状”应力集中区，且倾向上部底板应力集中区倾斜程度大于倾向下部；而在采空区底板形成了非对称反拱形应力释放区。受此影响，工作面倾向下部底板变形破坏深度大于倾向上部，整体呈“下大上小”的非对称破坏形态。在不同外力扰动下，直接底裂隙贯通并形成“三角形”、“梯形”、“矩形”滑移体，其中“三角形”滑移体失稳概率最大，“梯形”次之、“矩形”滑移体失稳概率最小。随着煤层倾角增加、支架载荷的增加、直接底厚度的减小，直接底滑移体概率增加。

Steeply inclined coal seams, defined as those with an inclination angle of 35°~55°, are internationally recognized as difficult mining coal seam. Steeply dipping coal seam are widely distributed in the deep mining areas of Eastern and western China, and the safe and efficient mining of this type of coal plays an important supporting role in promoting the coordinated development of regional economy in China. During the mining of steeply inclined coal seams, the loading process and deformation failure characteristics of the floor are significant difference from near horizontal coal seam mining due to the influence of coal seam dip angle, which leads to difficulty in stability control. Therefore, it is of great theoretical and engineering significance to study the deformation and failure mechanism to promote the safe production of floor in steeply dipping coal seam. This paper adopted the comprehensive research methods of physical similarity experiments, numerical simulations, and theoretical calculations to systematically study and analyze the formation and evolution of stress, deformation and failure mechanisms in the floor of steeply inclined coal seams during longwall mining. The results show:

(1) During the mining process of steeply dipping coal seam, the unloading expansion of the floor produces bed separation cracks to form a slip body, and slides out along the slip surface under its own gravity. The falling gangue slides along the dip of the working face to form a non-uniform filling zone with lower 'filling', middle 'filling' and upper 'partially suspended'. Due to the influence of non-uniform filling of caving gangue and unbalanced pushing load of upper coal body, the load and constraint characteristics of floor show obvious asymmetry tendency along the working face. The asymmetry of the load and constraint characteristics of the floor leads to the failure depth and fracture length of the floor in the lower part of the working face are larger than those in the upper part. With the increase of the advancing distance of the working face, the vertical displacement of the floor and the peak abutment pressure of the upper and lower coal bodies tend to increase first and then stabilize.

(2) Under the action of mining disturbance, the vertical shear stress t_zx and t_zy of the floor increase, and the direction of the principal stress deflects, forming a new mining stress transfer path, resulting in the change of the stress state of the floor. The floor in front of the coal rib of the working face is in a three-dimensional compression state, which is prone to compression-shear failure; the goaf floor is in a unidirectional and bidirectional tensile state, which is prone to tensile failure. When the advancing distance of the working face is greater than 3 times the length of the working face, the deflection law and size gradient characteristics of the principal stress direction of the floor gradually tend to be stable, resulting the peak abutment pressure in front of the working face showing an evolution trend of increasing first and then stabilizing.

(3) Affected by the dip angle of coal seam, the stress transfer path of floor is asymmetric arch distribution in the tendency section of working face. Inside the stress envelope arch, the principal stress of the bottom plate is reduced, the direction is obviously reduced, and the tensile area is formed. Outside the stress envelope arch, the overlying rock load of the upper and lower sides of the working face is transmitted to the floors on both sides of the stress deflection boundary. In the strike section of the working face, the stress transfer path of the floor is symmetrically flat arched. With the increase of coal seam dip angle, the arch height of stress envelope presents the evolution trend of decrease-increase-decrease. Affected by this, the stress concentration coefficient of the upper coal body of the working face also shows an increasing-decreasing-increasing evolution trend, while the lower coal body of the tendency shows a decreasing-increasing-decreasing evolution trend, and the position of the stress deflection boundary gradually migrates to the lower floor of the working face.

(4) The stope floor forms an inclined 'ellipsoid' stress concentration area, and the inclination degree of the upper floor stress concentration area is greater than that of the lower part. The asymmetric inverted arch stress release zone is formed in the goaf floor. Affected by this, the deformation and failure depth of the floor in the lower part of the working face is greater than that in the upper part, and the whole is an asymmetric failure form of ' large in the lower part and small in the upper part '. Under different external force disturbances, the direct bottom cracks penetrate and form ' triangle ', ' trapezoid ' and ' rectangular ' slip bodies. Among them, the instability probability of ' triangle ' slip body is the largest, followed by 'trapezoid' and ' rectangular ' slip body. With the increase of coal seam dip angle, the increase of support load and the decrease of direct bottom thickness, the probability of direct bottom slip body increases.