特厚煤层卸压综放开采基础研究

The occurrence of western region has a large number of more than 20m thick coal seam, most of them can't be performed by the surface mining method. There is no mature theory and technique for reference all around the world. How to excavate this kind of coal seam in underground is a worldwide issue. This research is creatively proposed the pressure releasing top-coal caving method by excavating the middle slice by using normal longwall mining in the extremely thick coal seam. There are several contents in this project：the top-coal broken mechanism, especially for the secondary broken mechanism in bottom slice by using top-coal caving mining; the top-coal caving mechanism and the basic theory of top-coal recovery improvement; mining-induced stress characteristic and ground control principle for the bottom slice by using top-coal caving mining. This technology is applicable to coal seam thickness, strength and large range of coal seam gas content. The top-coal recovery rate is high, also it is helpful to reduce the mining cost. The research object is divided into two parts: one is for more than 20m horizontal thick coal seam; another is for more than 20m extremely inclined thick coal seam. Due to the project is a new creativity technology, so the research issue is innovative. The project is the of basic theoretical research for more than 20m thick coal seam mining. It is accord with the National Natural Science Foundation sponsor strategy. So this research has important scientific significance and application value.

我国西部地区赋存有大量20m以上特厚煤层，其中大部分无法实现露天开采，国内外均没有成熟的理论与技术可借鉴。如何实现这类煤层安全高效的地下开采是一直没有解决的世界性难题。项目创造性地提出了特厚煤层预采中部分层的卸压综放开采技术，并针对性地开展特厚顶煤的垮落破碎机理以及在综放采动作用下的二次破碎机理、特厚顶煤放出规律及提高顶煤回收率的基础理论、底部综放工作面的采动应力特征及围岩控制原理研究。该技术适用于煤层厚度、强度和煤层瓦斯含量范围大，顶煤回收率高，有利于降低开采成本。研究对象分为两类，一类是20m以上近水平特厚煤层，另一类是20m以上的急倾斜特厚煤层。由于项目提出的开采技术是创造性的新技术，所以研究的问题也是创新性的。项目是为我国20m以上特厚煤层开采技术开发进行前期的基础理论研究工作，符合国家自然科学基金资助战略，具有重大科学意义与应用价值。

20m以上特厚煤层卸压综放开采过程中，顶煤最大和最小主应力均存在超前峰值现象，最大主应力始终处于加载状态，最小主应力则经历加载→卸载→反向加载三个过程；煤壁前方最大和最小主应力方向在平行于推进方向的垂直平面内同步向采空区旋转，最小主应力在水平面内的旋转角度同推进方向与初始最小地应力方向之间的夹角相等，最大主应力在水平面内不旋转；推导出顶煤裂隙发生I、II和I-II型扩展的应力场条件和优势扩展裂隙角确定方法，由于主应力增大和主方向旋转，顶煤裂隙首先发生I型扩展，最大主应力峰值附近，顶煤裂隙在高围压作用下发生II型扩展，煤壁附近，顶煤裂隙在开挖卸荷作用下发生I-II混合型扩展。卸压开采阶段顶煤顶板垮落空间形态呈近似梯形，支架上方台阶状顶煤悬臂梁结构的破断和失稳具有周期效应，上位顶煤位移>中位顶煤位移>下位顶煤位移，基本顶初次来压后出现切顶压架事故。综放开采阶段，短悬臂梁结构最终破碎成散体结构，且中位顶煤的总位移大于上位顶煤。由于支架的支撑作用，下位顶煤中产生明显的竖直裂隙，受支架影响的顶煤厚度约为10 cm。顶煤位移场、矢量场演化特征和实验结果一致。卸压工作面推进75cm时，500cm3以内的顶煤块体密集，占比约为94%，数量达到860个。推进135cm时，体积为500cm3以内的顶煤块体比例增加了2%，块体数量增加至1000个。当综放工作面推进17cm时，与卸压完毕相比，累计体积为500cm3以内的顶煤块体最为密集，块体比例增加了3.9%，块体数量增加了3640个，二次破碎效果显著。卸压开采阶段工作面顶煤破碎块度分布对综放阶段顶煤放出规律有明显影响，基于自主研发的三维精细化放煤模拟实验系统，揭示了顶煤破碎块度均值和标准差对顶煤放出体形态、煤岩分界面演化及顶煤回收率变化的影响；提出了基于顶煤相对块度的顶煤回收率预测模型，给出了最佳顶煤破碎块度阈值；优化了卸压开采方式下二次综放工作面的放煤工艺，提高了工作面顶煤回收率；升级了顶煤回收率测试装置，为卸压开采工作面现场测试奠定了基础。