煤层底板卸荷扰动断裂机制宏细观研究

基于断裂力学和重整化群理论,采用综合研究方法,从宏细观角度对开采扰动底板损伤岩层动态失稳机理进行了研究。结果表明,煤层回采后,底板岩层存在高应力束组成的主应力拱,最大主应力大小决定裂纹的起裂与扩展,裂纹的生长路径受控于最大主应力的方向。采场高支承压力引起岩层原始裂纹起裂,宏观上表现为底板岩层的预先剪切随机破坏;近场区域最大主应力场部分偏转,引起底板岩层中垂直应力显著降低、浅部水平应力急剧增加和斜向采空区方向产生高剪应力,迫使裂隙在原有扩展长度基础上进一步生长;工作面继续推进,采空区内底板岩层水平方向上压缩和竖向膨胀引起岩层拉破坏,当底板岩层损伤发展到临近损伤值时,极小范围的扰动被强烈放大,底板岩层由随机破坏转为"雪崩"式宏观断裂。

On the evolution mechanism of the fracture instability due to the coal floor damage caused by the mining exploitation

The paper intends to make a comprehensive study of the dynamic instability mechanism of the damaged floor strata under the condition of mining exploitation on the basis of the fracture mechanics and the renormalization group theory both from the macro and micro points of view.The results show that there exists a major stress arch composed of high stress bunch in the coal seam when the coal mining operation was completed.As a result,neither the crack initiating nor its propagating can be controlled at the major principal stress level in the said stress direction.What is more,the partial major principal stress tends to deflect in the working face area nearby,which is likely to make the vertical and horizontal stress suffer immediately and aggravate it at the shallow areas.Moreover,great sheamtress may tend to spread to the goaf,which would naturally lead to the crack growth from the originally already cracked sections.Thus,with the further and further advancement of the working face,it will be inevitable to cause the horizontal compression and the vertical swelling,which may in turn lead to the tensile damage of the rock strata.If the part of the damaged coal seam grows to a critical extent,the mining disturbance in a range of the very narrow sphere would be spreading quickly and in turn result in a random damage of coal seam so as to lead to a disastrous avalanche.Thus,the result of our study can help to promote and enrich the theory of the mining pressure and strata control.Besides,the so-called newly evolved fracture instability mechanism concerning the coal seam damage due to the mining exploitation accumulation can be expected favorable for the evaluation practice in the deep coal mining exploitation.They are also useful to forecast the danger zone of the water inrush from the coal floor and the time distribution of water gushing-out,to predict the scale of the effects in the fiat and longdistance mining at the upper level underlying low burst coal protective coat.