无煤柱自成巷预裂切顶机理及其对矿压显现的影响

Mechanism of roof presplitting in a nonpillar mining method with entry automatically retained and its influence on the strata behaviors

预裂切顶是无煤柱自成巷技术的核心,预裂切顶的效果直接关系到成巷的稳定性。以柠条塔煤矿无煤柱自成巷工程项目为背景,首先运用理论分析方法研究了预裂切顶的机理,进而运用离散元数值模拟方法和现场试验方法,对不同切顶条件下巷道围岩的响应规律进行了研究。研究发现,非聚能爆破模式下裂隙向四周扩展,导致巷道顶板形成裂隙分支,破坏巷道顶板的完整性。聚能张拉爆破模式下,应力波在侵彻裂隙的导向作用下可实现定向成缝。为达到理想的切顶效果,装药量及孔间距需协调设计,以保证孔间裂隙贯通。切顶参数变化对巷道围岩的整体变形及矿压分布有重要影响。在一定范围内,增大切顶高度可增大矸石碎胀体积,减小巷道顶板变形和作用在实体煤帮上的应力峰值,但切顶高度不宜过大,否则会增大施工难度,且会增大留巷变形。切顶角度对矿压显现亦有一定影响。当垂直巷道顶板切缝时,巷道围岩变形最大,但当切缝向采空区偏斜10°~20°,留巷围岩变形明显减小。柠条塔煤矿4.1 m采高、砂岩为主顶板的条件下,爆破孔间距为600 mm,单孔装药量为3 200 g时,切顶高度设计为9.0 m,切顶角度为10°时,矸石垮落充分,成巷效果较好。总结认为,切顶高度影响的是采空区矸石的碎胀体积及其对切顶短臂结构的作用力,切顶角度主要影响采空区顶板在垮落中对切顶短臂结构的动态下坠力及稳定后对切顶短臂结构的稳态支撑力,无煤柱自成巷预裂切顶的关键是保证采空区顶板和巷道顶板切得开,在切顶参数设计时应综合考虑预裂效果和切顶后碎胀矸石与切顶短臂结构的作用关系。

The directional roof presplitting technology is the core of the nonpillar mining method with entry automatically retained.The effects of roof presplitting directly influence the stability of the retained entry.Based on the engineering practice in Ningtiaota coal mine,China,the theoretical analysis method was used to investigate the mechanism of directional roof presplitting,and the influence of roof presplitting on the sur-rounding rock behaviors was studied by discrete element numerical simulation and field experiment.The results show that the cracks propagated in random directions in the entry roof under the conventional blasting condition,and the integrity of the entry roof was easily destroyed.However,under the energy-accumulated tensile blasting condition,the directional crack could be generated under the guidance of original penetrated crack.To achieve ideal roof cutting effects,the charging amounts and blast hole distance should be harmoni-ously designed.The roof cutting parameters had an important influence on the deformation and stress distri-bution in the entry surroundings.Within a certain range,the increase of roof cutting height could increase the bulking volume of the gob roof,reduce the deformation of the entry roof and reduce the stress concentration in the integrated coal rib.However,when the cutting height was too large,the construction difficulty increased,and it was not conducive to the stability of the retained entry.When the cutting direction was vertical to the roof,the deformation of the entry surroundings was the largest.When there was a rational angle(10°-20°) between the roof cutting and vertical direction,the deformation of the entry surroundings was significantly reduced.Field test shows that when the roof cutting height was 9.0 m,roof cutting angle was 10°,the distance between blast holes was 600 mm,the charging amount of a single hole was 3 200 g,the gob roof could fully collapse and the final entry retaining effects were satisfactory in the Ningtiaota coal mine.It is concluded that the roof cutting height affects the bulking gangues and its action on the short arm roof rock structure,whereas the roof cutting angle affects the dynamic dropping force and steady supporting force acting on the short arm roof structure during caving and stabilizing processes.The key of the roof splitting in the new nonpillar mining method is cutting off the connection of the gob and entry roof.The roof splitting effects and interactive relationship between the gangues and short arm roof rock structure should be comprehensively considered when the roof cutting parameters are designed.