浅埋单一关键层断裂覆岩压力成拱效应及分布特征

The pressure arching effect and distribution characteristics of fractured strata of single key layer under shallow buried condition

我国神东矿区赋存有大量埋深浅且基岩薄的厚煤层,浅埋长壁工作面顶板岩层结构形式和矿压显现具有特殊性,为探究采场断裂覆岩荷载传递特征及承载状态,针对浅埋薄基岩工况条件下断裂结构顶板岩层压力传递成拱特点,以单一关键层断裂覆岩为研究对象,根据采场断裂岩层回转下沉运动中的典型受压状态,讨论岩层接触面和关键块内压应力传递路径及分布特征,分析覆岩关键块内集中压应力的拱效应形成机制。通过构建断裂覆岩铰拱结构力学模型,解析推导了对应覆岩铰拱结构的拱轴力求解公式,分析了周期断裂覆岩关键块回转接触特征及应力传递规律。以神东矿区大柳塔矿典型浅埋单一关键层煤层开采为工程背景,利用块体离散元UDEC软件构建煤岩层数值模型,考虑工作面沿最大主应力方向推进情况,对不同采动阶段断裂覆岩结构形式和主应力演化特征进行模拟分析,获得了初次断裂及周期断裂覆岩承载区域分布规律。结果表明:成拱区域拱脚、拱肩和拱顶区域主应力分布符合二次函数抛物线规律,拱脚主应力沿竖直方向由下向上呈递减分布,而拱肩和拱顶主应力呈递增分布,拱腰主应力分布呈过渡性变化。通过分析主应力集中带关键部位最大主应力拟合规律及垂直应力分布特征,明确了主压应力成拱效应影响下铰拱结构、台阶结构和砌体梁结构断裂覆岩前后支撑区域的承载状态。

A large amount of thick coal seams with shallow depth and thin bedrock occur in Shendong mining area of China. The structure form and weighting appearance of roof strata of shallow longwall working face show some specific characteristics. In order to explore the load transferring characteristics and load bearing state of the fractured overburden strata in the mining area, in terms of the arching characteristics of transferred pressure in fractured roof under the condition of shallow thin bedrock, taking the fractured single key strata as research object, according to the typical compressed state of fractured strata of mining area during rotary subsidence, this paper discussed the transferring path and distribution characteristics of compressive stress in the key strata block and its contacting surface, and analyzed the forming mechanism of arching effect of concentrated compressive stress in key strata block. By building the mechanical models of hinged arch structure of fractured overlying strata and deducing the analytical solution formula for the arch axial force of corresponding arch structure of strata, the rotary contacting characteristics and stress transferring law of key blocks in periodic fractured strata were studied. Taking the typical mining condition of shallow coal seam with single key layer in Daliuta mine of Shendong mining area as engineering background, using the block discrete element software UDEC to build a numerical model of coal seam and strata, considering the condition that the working face advancing along the direction of major principal stress, the evolution characteristics of principal stress and structure form of fractured strata at different mining stages are simulated, and the distribution law of the load bearing area of initial and periodic fractured strata were obtained. The results show that the distribution of principal stress in the region of arch foot, arch shoulder and arch top conforms to the parabolic law of quadratic function, the principal stress of the arch foot decreases from the bottom to the top along the vertical direction, while the principal stress of the arch shoulder and the arch top increases along the vertical direction and the principal stress of the arch waist changes in a transitional way. By analyzing the fitting law of the major principal stress and the vertical stress distribution characteristics of the key parts of the concentrated principal stress zone, the load bearing conditions at the front and rear support area of hinged arch structure, step structure and voussior beam structure of fractured strata were identified under the arching effect of principal compressive stress.