无煤柱切顶沿空留巷是近年来提出的一种能够提高煤炭资源回收率的煤炭开采新技术，在国内各矿区正在大力推广和应用。但该技术在底板水害严重的华北型煤田应用时，还存在着煤层底板破坏规律与机理及底板突水危险性预测方法等问题亟需研究解决。本文以受奥灰承压水威胁的澄合矿区典型煤矿为例，采用钻探窥视、压水实验、孔间电阻率成像、底板破坏微应变监测等现场实测手段，结合岩石力学参数测试、物理相似模拟、数值模拟、理论分析、统计分析等方法，对无煤柱切顶沿空留巷开采方法下煤层底板破坏规律、破坏机理，以及底板破坏深度与突水危险性预测方法进行研究，以期为无煤柱切顶沿空留巷开采底板突水危险性预测、评价、治理提供理论和技术支撑。

基于孔间电阻率成像、钻孔窥视、压水实验等综合探测手段，揭示了无煤柱切顶沿空留巷底板破坏深度发育规律。底板最大破坏深度 11m，位于工作面边缘切顶线附近，破坏深度呈现由工作面边缘向中部逐渐变小直至稳定的变化规律。依据工作面推采底板微应变监测结果划定了底板采动超前影响区（7.1m~20m），采动应力剧烈区（7.1m~-55m），采动应力恢复区（＜-55m）。明确了切顶作用对于底板破坏的影响范围在留设巷道两侧20m 范围以内，切顶侧采空区底板最大破坏深度较未切顶侧有一定降低。

通过数值模拟、物理相似材料模拟、力学模型分析，分析了无煤柱切顶沿空留巷底板应力场、位移场及破坏演化特征，揭示了无煤柱切顶沿空留巷底板破坏机理及空间分布机理。研究发现，底板应力场、位移场和破坏具有“非对称式演化特征”。工作面走向方向垂直应力呈“单峰”分布，即由回采位置向工作面前方垂直应力由低增高再降低。倾向方向应力分布呈非对称式分布，切顶留设巷道附近 14m 范围内、工作面前方与侧方支承压力峰值较留设煤柱侧有显著降低，降低幅度在 5%~20%。工作面底板扰动深度随超前工作面距离的缩短直至采空区后方呈现增大→减小→增大→稳定的演化特征，切顶留巷侧底板扰动深度有一定幅度减小。底板破坏演化分别经历了超前切顶扰动破坏、卸压破坏、压实稳定破坏三个阶段。压实稳定破坏以工作面边缘侧向支承压力差所导致的压剪破坏为主，为底板岩体最大破坏深度所处位置，底板破坏深度切顶侧较留设煤柱侧减小幅度在 10%左右。开采所引起的底板应力场的周期性变化是导致底板破坏的直接原因。首采工作面底板破坏呈现的非对称式分布主要由切顶卸压所导致的工作面两侧应力集中程度的显著差别引起，相邻工作面底板破坏呈现的非对称式分布主要由工作面间煤柱的取消、切顶卸压两方面因素共同导致。揭示了切顶高度与切顶角度是控制底板破坏发育的直接影响因素。提出了以切断顶板应力传播路径、减小切顶接触面间摩擦阻力、实现切落岩体充分垮落为标准的底板破坏控制切顶参数确定方法。

基于开采深度、开采高度、工作面斜长、切顶高度、切顶角度五因素四水平底板破坏深度正交数值模拟实验，提出了无煤柱切顶沿空留巷底板破坏深度预测方法。揭示了无煤柱切顶沿空留巷底板破坏深度各主控因素与底板破坏深度整体呈近线性关系，当主控因素值过大时，底板破坏深度表现为多因素耦合控制。建立了基于开采深度、开采高度、工作面斜长、切顶高度、切顶角度的底板破坏深度多元线性回归预测模型。

通过建立隔水关键层四边固支薄板力学模型，分析隔水关键层挠度、应力特征，构建了无煤柱切顶沿空留巷底板隔水关键层突水力学判据。揭示了关键层厚度、工作面斜长、关键层抗压强度、垮落带高度、工作面长度各因素与底板突水危险性整体呈近线性关系，当工作面长度过大、隔水关键层强度较小时，底板突水危险性表现为多因素耦合控制。基于隔水关键层突水力学判据，以倾向方向开采底板破坏的充分采动为隔水关键层边界条件判定标准，提出了无煤柱切顶沿空留巷首采工作面、相邻工作面及后续工作面底板突水危险性预测方法。突水危险性从高到低依次为相邻工作面＞首采工作面＞后续工作面。随着开采工作面的增加，底板突水危险性最大值由首采工作面中心位置依次演化至切顶留设巷道附近及后续工作面中心位置。开采工作面的增加使无煤柱切顶沿空留巷对底板隔水关键层的保护作用愈发显著。

Gob-side entry retaining with roof cutting and no pillar mining is a new Coal mining technology proposed in recent years, which can improve the recovery rate of coal, and is being vigorously promoted and applied in domestic mining areas. However, when this technology is applied in North China type coal fields with severe floor water damage, there are still problems that need to be studied and solved, such as the law and mechanism of floor failure and the prediction method of floor water inrush risk. Taking the typical coal mine in Chenghe mining area threatened by Ordovician limestone confined water as an example, this paper uses on-site measurement methods such as drilling peeping, water pressure experiment, resistivity imaging between holes, and monitoring of floor failure micro strain, combined with rock mechanics parameter testing, physical similarity simulation, numerical simulation, theoretical analysis, statistical analysis and other methods. Conduct research on the failure law, failure mechanism, as well as the prediction method of floor failure depth and water inrush risk of gob-side entry retaining with roof cutting and no pillar mining, in order to provide theoretical and technical support for the prediction, evaluation, and treatment of the risk of water inrush from the floor of gob-side entry retaining with roof cutting and no pillar mining.

Based on comprehensive detection methods such as inter hole resistivity imaging, borehole peeping, and water pressure experiments, the development law of floor failure depth of gob-side entry retaining with roof cutting and no pillar mining has been revealed. The maximum failure depth of floor is 11meters, located near the cutting line of the working face edge. The failure depth gradually decreases from the working face edge to the middle and stabilizes. Based on the microstrain monitoring results of floor in the working face, the front mining impact area (7.1~20 meters), the intense mining stress area (7.1~-55 meters), and the mining stress recovery area (<-55 meters) were determined. It has been clarified that the impact of roof cutting on the floor failure is within a range of 20 meters on both sides of the reserved roadway. The maximum depth of the floor failure in the roof cutting side is slightly lower than that on the non roof cutting side.

Through numerical simulation, physical similarity material simulation, and mechanical model analysis, the stress field, displacement field, and failure evolution characteristics of the floor of gob-side entry retaining with roof cutting and no pillar mining were analyzed, revealing the failure mechanism and spatial distribution mechanism of the floor of gob-side entry retaining with roof cutting and no pillar mining. Research has found that the stress field, displacement field, and floor failure exhibit "asymmetric evolution characteristics". The vertical stress in the direction of the working face shows a "single peak" distribution, that is, the vertical stress increases from low to high and then decreases from the mining position to the front of the working face. The stress distribution in the inclined direction shows an asymmetric distribution, and the peak pressure of the support in front of and on the side of the working face within a range of 14 meters near the roof cutting reserved roadway has significantly decreased compared to the reserved coal pillar side, with a reduction range of 5% to 20%. The disturbance depth of floor shows an evolutionary characteristic of increasing, decreasing, increasing, and stabilizing with the shortening of the distance from the advance working face to the rear of the goaf. The disturbance depth of the roof cutting retaining roadway side floor has a certain degree of reduction. The evolution of floor failure has gone through three stages: advanced roof cutting disturbance failure, unloading failure, and compaction stability failure. The compaction stability failure is mainly caused by compression shear failure caused by the lateral support pressure difference at the edge of the working face, which is the position where the maximum failure depth of floor rock mass is located. The depth of floor rock failure on the roof cutting side is reduced by about 10% compared to the reserved coal pillar side. The periodic changes in the stress field of the floor caused by mining are the direct cause of floor failure. The asymmetric distribution of the floor failure in the first mining face is mainly caused by the significant difference in stress concentration on both sides of the working face caused by roof cutting and pressure relief. The asymmetric distribution of the floor failure in adjacent working face is mainly caused by the cancellation of coal pillars between working faces and the combined factors of roof cutting and pressure relief. It has been revealed that the height and angle of roof cutting are the direct influencing factors controlling the development of floor failure. A method for determining the cutting parameters of floor failure control is proposed based on the criteria of cutting off the stress propagation path of roof, reducing the frictional resistance between the cutting roof contact surfaces, and achieving full collapse of the cutting rock mass.

Based on the orthogonal numerical simulation experiment of floor failure depth was conducted to select five factors, namely mining depth, mining height, working face slope length, roof cutting height, and roof cutting angle, in four levels, a prediction method for floor failure depth of gob-side entry retaining with roof cutting and no pillar mining is proposed. It has been revealed that the main control factors of floor failure depth of gob-side entry retaining with roof cutting and no pillar mining have a nearly linear relationship with floor failure depth. When the value of the main control factors is too large, the floor failure depth shows a coupling control of multiple factors. A multiple linear regression prediction model for floor failure depth based on mining depth, mining height, working face slope length, roof cutting height, and roof cutting angle has been established.

Through establishing the mechanical model of the four side fixed support thin plate of the waterproof key layer, analyzing the deflection and stress characteristics of the waterproof key layer, the hydraulics criterion of water inrush of the waterproof key layer in the floor of gobside entry retaining with roof cutting and no pillar mining was constructed. The key layer thickness, working face slope length, compressive strength of the key layer, height of the collapse zone, and working face length are revealed to have a nearly linear relationship with the overall risk of floor water inrush. When the working face length is too large and the strength of the waterproof key layer is low, the risk of water inrush from the floor manifests as a multi factor coupling control. Based on the hydraulics criterion of waterproof key layer inrush, and the criteria for determining the boundary condition of the key waterproof layer are based on the sufficient mining of floor failure in the inclined direction of mining, a prediction method for the water inrush risk of the first mining face, adjacent working faces, and subsequent working faces in gob-side entry retaining with roof cutting and no pillar mining has been proposed. The order of water inrush risk from high to low is adjacent working face>first mining face>subsequent working face. As the mining face increases, the maximum risk of floor water inrush evolves from the center position of the first mining face to the vicinity of the roof cutting reserved roadway and the center position of the subsequent working faces. The increase in mining face has made the protective effect of gob-side entry retaining with roof cutting and no pillar mining on the key layer of floor waterproof more significant.