采动过程中坚硬顶板结构破断失稳瞬间释放能量易诱发冲击灾害。特别是在蒙陕矿区，随着开采深度增加，煤层上方存在多层坚硬顶板，其复合作用下顶板结构失稳诱冲机理复杂，难以识别主要控制层位，导致顶板预裂弱化控灾经济效益受到制约。通过分析开采过程中复合坚硬顶板破断运移机制以及不同层位坚硬顶板预裂卸压机理，为复合坚硬顶板强矿压灾害治理奠定理论基础和提供有益借鉴。

论文以纳林河二号矿井31104工作面为背景，综合采用物理相似模拟实验、数值计算、理论分析及现场实测相结合的方法，对复合坚硬顶板条件下大采高工作面覆岩变形运移特征、矿压显现规律、不同层位坚硬顶板水力压裂特征等进行探究，主要研究结果如下：

（1）由关键层理论计算得出纳林河31104工作面上方100 m范围内存在2层关键层，通过复合坚硬顶板判定准则计算分析出工作面上覆16.0 m下位坚硬顶板、上覆53.9 m上位坚硬顶板会形成复合坚硬顶板。复合坚硬顶板工作面充分采动前，下位坚硬顶板易形成悬臂梁结构，其周期性破断、回转失稳充填采空区，对上部岩层形成强支撑约束作用，导致上位坚硬岩层易形成砌体梁结构，推进至一次见方时，上位砌体梁结构回转失稳协同下位悬臂梁结构切落失稳，造成采空区强矿压现象。

（2）下位坚硬顶板和上位坚硬顶板的破断运动对工作面的稳定性有重要影响。构建了复合坚硬顶板的力学模型，对不同层位坚硬顶板破断回转进行了理论分析，推导了直接顶对上部不同层位垮落岩层的支承应力公式及上、下位坚硬顶板转动惯量。通过分析不同层位坚硬顶板的运移规律，将复合坚硬顶板的破断运移分为三个阶段：下位坚硬顶板悬臂梁结构周期性破断阶段、下部岩层约束作用下上位坚硬顶板弯曲下沉阶段以及上位坚硬顶板砌体梁结构、下位坚硬顶板悬臂梁结构协同失稳阶段。

（3）不同层位坚硬顶板预裂对工作面围岩应力和位移的影响不同，预裂上位坚硬顶板相比预裂下位能够更加有效地释放顶板应力，降低煤壁应力集中，增大顶板破坏高度和破坏程度，表明上位坚硬岩层为主要控制层位。对上位坚硬顶板进行预裂弱化能更有效地提高复合坚硬顶板破断频次，避免上-下位坚硬顶板协同作用，对破断回转幅度和能量进行抑制，现场监测结果与实验现象基本一致，表明对上位坚硬岩层进行水压预裂弱化有效避免了工作面冲击灾害，从而实现复合坚硬顶板冲击地压的协同有效治理。

In the process of mining, the energy released at the moment of fracture and instability of hard roof structure is easy to induce impact disaster. Especially in the Mengshaan mining area, with the increase of mining depth, there are multi-layer hard roofs above the coal seam. Under the combined action, the instability mechanism of the roof structure is complex, and it is difficult to identify the main control horizon, resulting in the weakening of the roof pre-splitting. The economic benefits of disaster control are restricted. By analyzing the mechanism of breaking and migration of composite hard roof and the mechanism of pre-splitting and pressure relief of hard roof in different layers in the mining process, it lays a theoretical foundation and provides useful reference for the treatment of strong rock pressure disaster of composite hard roof.

Based on the 31104 working face of Nalinhe No.2 Mine, this paper comprehensively uses the methods of physical similarity simulation experiment, numerical calculation, theoretical analysis and field measurement to explore the deformation and migration characteristics of overburden rock, the law of mine pressure appearance and the hydraulic fracturing characteristics of hard roof in different layers under the condition of composite hard roof. The main research results are as follows :

(1) According to the key stratum theory, it is calculated that there are two key strata within 100 m above the 31104 working face of Nalin River. Through the determination criterion of composite hard roof, it is calculated and analyzed that the upper 16.0 m lower hard roof and the upper 53.9 m upper hard roof will form a composite hard roof. Before the full mining of the composite hard roof working face, the lower hard roof is easy to form a cantilever beam structure, and its periodic fracture and rotary instability fill the goaf, forming a strong support constraint effect on the upper rock strata, resulting in the upper hard rock strata easy to form a masonry beam structure. When advancing to one square, the rotary instability of the upper masonry beam structure cooperates with the cutting instability of the lower cantilever beam structure, resulting in strong mine pressure in the goaf.

(2) The breaking movement of the lower hard roof and the upper hard roof has an important influence on the stability of the working face. The mechanical model of the composite hard roof is constructed, and the theoretical analysis of the fracture rotation of the hard roof in different layers is carried out. The bearing stress formula of the immediate roof to the caving strata in different layers of the upper part and the rotational inertia of the upper and lower hard roofs are derived. By analyzing the migration law of hard roof in different layers, the fracture migration of composite hard roof is divided into three stages : the periodic fracture stage of cantilever beam structure of lower hard roof, the bending and sinking stage of upper hard roof under the constraint of lower rock strata, and the synergistic instability stage of masonry beam structure of upper hard roof and cantilever beam structure of lower hard roof.

(3) The pre-splitting of hard roof in different layers has different effects on the stress and displacement of surrounding rock in working face. The pre-splitting upper hard roof can release the roof stress more effectively than the pre-splitting lower hard roof, reduce the stress concentration of coal wall, and increase the damage height and damage degree of roof, indicating that the upper hard rock layer is the main control layer. The pre-splitting weakening of the upper hard roof can more effectively improve the breaking frequency of the composite hard roof, avoid the synergistic effect of the upper and lower hard roofs, and suppress the breaking rotation amplitude and energy. The field monitoring results are basically consistent with the experimental phenomena, which shows that the hydraulic pre-splitting weakening of the upper hard rock layer effectively avoids the impact disaster of the working face, so as to realize the synergistic and effective treatment of the impact ground pressure of the composite hard roof.