二维拉张爆破定向致裂机理研究及工程应用

Study on directional fracturing mechanism and field application of two-dimensional tensile blasting

  • 摘要: 钻爆法在岩体开挖领域得到了广泛应用,定向断裂控制爆破是其中的重要应用方向之一。为此,针对岩石材料力学特性,提出一种爆破后仅在孔壁预设方向产生一个近似二维单裂面的控制爆破技术——二维拉张爆破。分析了二维拉张爆破定向致裂原理,采用自主研制的试验系统开展了二维拉张爆破可视化试验,并在煤矿现场进行了二维拉张爆破定向切顶试验。研究结果表明:(1)二维拉张爆破技术通过非炸药材料(膨胀剂)瞬间反应在孔内产生高温高压气体对介质产生瞬时胀裂效果,并通过二维拉张爆破装置控制裂缝起裂及扩展方向;(2)二维拉张爆破技术通过二维拉张爆破装置的调控作用使得孔壁在预裂方向产生集中拉应力,从而通过拉张作用在试件预裂方向产生I型裂缝,变常规炸药爆破的随机、分区破裂为定向、单一破裂;(3)二维拉张爆破技术在复合顶板条件下可取得理想的定向断裂效果,有望为井工煤矿巷道定向切顶卸压提供一种非炸药爆破方法。研究结果有助于揭示二维拉张爆破机理,促进二维拉张爆破技术在定向破岩领域的应用。

     

    Abstract: The drilling and blasting method has been widely used due to its efficiency, ubiquity, and cost-effectiveness in the field of rock excavation, and directional fracture-controlled blasting is one of the important applications. Therefore, in response to the characteristic that the tensile strength of rock mass is much lower than its compressive strength, a blasting technique called two-dimensional tensile blasting (2D blasting) is proposed, which only produces an approximate two-dimensional single crack surface in the predetermined direction of the hole wall after blasting. The directional fracturing principle of 2D blasting was analyzed, the visualization experiments on the expansion of two-dimensional tension blasting cracks were conducted using a self-developed experimental system, and a directional roof cutting test using 2D blasting technology waw conducted at an actual coal mine. The research results indicate that: (1) The 2D blasting generates high-temperature and high-pressure gas in the hole through the instantaneous reaction of expander, which produces instantaneous expansion and cracking effect on the medium, meanwhile controls the direction of crack initiation and propagation through 2D blasting device. (2) The 2D blasting generates concentrated tensile stress on the hole wall in presplitting direction through the control of the 2D blasting device, resulting in mode I cracks through tensile fracturing, transforming the random and partitioned rupture of conventional blasting into a directional and single rupture. (3) Compared with conventional blasting, 2D blasting has a longer reaction time after initiation, about 200 ms, while conventional blasting only has less than 0.2 ms, a difference of 1000 times. This indicates that 2D blasting technology has a much smaller loading rate than conventional explosive blasting, resulting in a much smaller strain rate in the specimen than conventional explosives. Therefore, the 2D blasting technology eliminates the blasting crushed zone and makes it easier to achieve the desired directional fracture effect. (4) The 2D blasting can achieve ideal directional fracture effect under the condition of composite roof. The observation results of 10 cut holes within a 100 m test section on site show that the average crack rate inside the holes can reach over 90%. Therefore, 2D blasting technology is expected to replace explosives and become a new type of directional pressure relief technology for the mine roadway. The research results contribute to revealing the mechanism of 2D blasting and promoting the application of 2D blasting technology in the field of directional rock breaking.

     

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