厚硬顶板地质条件的矿井在我国分布极为广泛，因其具有岩石强度高、裂隙发育低以及不易自然垮落等特点，致使工作面采场、巷道及保护煤柱等长时间处在高应力、高扰动的状态，从而引起顶板矿压显现强烈，煤柱失稳及巷道严重变形等问题。因此，探究坚硬顶板的控制方法及机理，其对矿井的安全、绿色及高效开采具有重要的科学与工程意义。基于此，本文以陕西榆林市小保当煤矿厚硬砂岩顶板水力切顶破断卸压工程为背景，采用理论分析、室内试验、数值模拟、现场应用相结合的研究方法，对厚硬砂岩顶板切顶卸压技术和机理以及现场应用进行了研究。论文取得的主要结论如下：

      （1）采用室内试验的方法对112203工作面顶板的岩样开展岩石单轴压缩试验、单轴抗拉强度试验和抗剪强度试验，掌握顶板不同岩性的基本特征参数，综合分析厚硬砂岩顶板的结构特征。

      （2）依据关键层理论，结合地质钻孔分析，利用载荷计算式以及变形和破断判别式对关键层进行判定，确定关键层的岩性、位置及厚度等基本特征。确定工作面上覆岩层中关键层分为3种，第3层为主关键层，第10层关键层为亚关键层，第15层、16层、17层为复合关键层。

      （3）通过“砌体梁”结构模型，研究了厚硬砂岩顶板的承载特征，运用切顶卸压技术破坏厚硬顶板整体结构，使得厚硬顶板上覆岩层充分垮落，上覆载荷向深部转移，减轻了上覆岩层对煤柱及巷道的压力，揭示了切顶卸压方法改善工作面巷道稳定性的作用机理。

      （4）利用UDEC离散元模拟软件对切顶卸压前后上覆岩层运动进行模拟，结果表明：经过切顶处理的上覆岩层基本沿预切裂缝断裂，上覆岩层的充分垮落使矸石充填采空区并承担上覆岩层压力，煤柱与巷道应力向深部转移，有效控制了巷道围岩变形。

      （5）在小保当煤矿112203工作面进行现场试验，试验发现压裂区与未压裂区相比，顶板位移减小51.25%，两帮位移减小51.28%，煤柱应力平均降低了约57%，结果表明切顶卸压技术明显起到了弱化顶板强度、转移应力的作用，改善了辅运巷道围岩的应力环境，降低补强支护成本。

        Mines with thick and hard roof geological conditions are widely distributed in our country. Because of its features of high rock strength, low fissure development and not easy to collapse naturally, etc., the working face quarry, roadway and coal pillar protection are in a state of high stress and high disturbance for a long time, which causes problems such as strong mineral pressure on the roof plate, unstable coal pillars, and serious deformation of the roadway, etc. Therefore, it is of great scientific and engineering significance to investigate the control methods and mechanisms of hard roof, which is of great importance for safe, green and high-efficiency mining. Therefore, it is of great scientific and engineering significance to explore the control methods and mechanisms of hard top plate for safe, green and efficient mining. Based on this, this paper takes the background of the hydrodynamic roof cutting and pressure relief project of Xiaobaodang Coal Mine in Yulin City, Shaanxi Province, and adopts the combination of theoretical analysis, indoor test, numerical simulation, and on-site application to investigate the technology, mechanism, and on-site application of roof cutting and pressure relief of thick and hard sandstone roof slabs. The main conclusions of the thesis are as follows:

        (1) The indoor test method was used to carry out rock uniaxial compression test, uniaxial tensile strength test and shear strength test on the rock samples of the top plate of the 112203 working face, to grasp the basic characteristic parameters of different lithologies of the top plate, and to comprehensively analyze the structural characteristics of the top plate of thick hard sandstone.

        (2) Based on the theory of key layer, combined with the analysis of geological drill holes, the key layer is determined by using the load calculation formula and the deformation and breakage discriminant formula, and the basic characteristics of the key layer such as lithology, location and thickness are determined. The key layers in the overlying rock layer on the working face are categorized into 3 types, the 3rd layer is the main key layer, the 10th key layer is the second key layer, and the 15th, 16th and 17th layers are the composite key layers.

        (3) Through the structural model of "masonry beam", the bearing characteristics of thick hard sandstone roof plate were studied, and the overall structure of thick hard roof plate was damaged by the top-cutting and depressurization technique, which made the overlying rock layer of the thick hard roof plate fully collapsed, and the overlying load was transferred to the deep part of the roof plate, thus reducing the pressure of the overlying rock layer on the coal pillar and the roadway, and revealed the function mechanism of top-cutting and depressurization to improve the stability of the roadway in the working face. It reveals the mechanism of improving the stability of the working face roadway by the method of cutting the roof and relieving the pressure.

        (4) Using UDEC discrete element simulation software to simulate the movement of the overlying rock layer before and after cutting the top and unloading the pressure, the results show that: after cutting the top of the treatment of the overlying rock layer is basically fractured along the pre-cutting cracks, the overlying rock layer collapses sufficiently so that the gangue fills the mining area and bears the pressure of the overlying rock layer, and the stresses of the coal pillar and the roadway are shifted to the deep part of the tunnel, which effectively controls the deformation of the surrounding rocks of the roadway.

        (5) Field test was carried out in 112203 working face of Xiaobaodang coal mine, and it was found that the displacement of roof plate was reduced by 51.25%, the displacement of two gangs was reduced by 51.28%, and the stress of coal pillar was reduced by about 57% on average compared with that in the area of fractured area and unfractured area, and the results showed that the technology of cutting top and unloading pressure obviously played the role of weakening the strength of roof plate and transferring the stress, improving the stress environment of the peripheral rock of auxiliary roadway and lowering the cost of reinforcing and supporting. The result shows that the top-cutting decompression technology obviously plays the role of weakening the roof strength and transferring the stress.