掏槽孔超深深度对爆破效果的影响

Experiment study on overdepth coefficient of the cut hole in coal mine roadway excavation blasting

  • 摘要: 煤矿岩巷钻爆施工中,速度的关键在于掏槽。随着岩巷掘进工程量不断增大,虽然炮孔深度逐渐增大,但是掏槽孔超出普通孔的长度并没有改变,基本保持在200 mm及以下。针对掏槽孔超深与炮孔利用率这一问题,本文在超深系数η的基础上,引入裂隙区重合度φ的概念,利用数学建模方法,分析了不同超深深度爆破时的岩石应力状态,建立了超深深度及岩石碎胀系数之间的关系,并确定了掏槽槽腔主要参数的计算公式及取值范围,发现存在最优掏槽孔超深系数η和裂隙区重合度φ,使得炮眼利用率最高。利用LS-DYNA数值模拟分析了掏槽孔超深爆破时爆炸应力波的传播规律和孔底岩石的受力特征,并比较了200、300、400和500 mm不同超深深度的应力波强度变化特征并应用于岩巷掘进现场,对比了超深爆破方案和普通爆破方案的单循环进尺、炮孔利用率、眼痕率及大块率等爆破效果指标。结果表明,当超深深度为400 mm时,炸药爆破能量充分用于破岩,能量利用率最高,爆破后形成重叠的裂隙区,增大了后续爆破的自由面,提高了爆破破岩的效率,对岩巷钻爆法施工的参数优化有一定的指导意义。

     

    Abstract: In rocky road drilling and blasting in coal mines, the key to work efficiency is cutting. Although blast hole depth has steadily increased with increasing rocky road excavation activities, the cut hole depth is still ordinarily shallow, which is normally kept at 200 mm or less. Using an intelligent design system, a key technology, and equipment matching research of a drilling and blasting method in the Huainan mining area as the engineering background, this paper conducts research on the overdepth coefficient of cutting holes and the optimization of cutting-blasting parameters, aiming at the excessive number of full section blast holes in the mining area and the randomness and irrationality of blast hole layout. The overdepth coefficient, η, was obtained by theoretical derivation, numerical modeling, field testing, and monitoring. Based on this, the coincidence degree of fracture area, φ, is also introduced. This paper analyzes the rock stress state and stress wave attenuation phenomenon during blasting with different overdepths, establishes the relationship between the overdepth and stress between cut holes, determines the calculation formula and value range of the key parameters of the cut cavity, and investigates whether there is an optimal cut hole overdepth coefficient. The coincidence degree with fracture area increases the explosive blasting energy utilization rate and provides a theoretical basis for decreasing the charge and number of holes while retaining the blasting impact. The propagation law of explosion stress wave and the distribution and evolution law of effective stress in rock mass during overdepth blasting of cutting holes at different depths are explored using LS-DYNA numerical simulation, and the variation characteristics of stress wave intensity at different overdepth stress measuring points are compared, based on the geomechanical parameters of surrounding rock in Gubei Coal Mine. The effect of varying cut hole depths on the free surface after blasting and the blasting effect is revealed; overdepth blasting schemes of 200, 300, 400, and 500 mm are applied to the rocky road excavation site. The blasting effect indicators such as single cycle footage, blast hole utilization rate, explosive unit consumption, block rate of each overdepth blasting scheme, and ordinary blasting scheme are compared, and the effect of different overdepths on the quality and effect of cutting-blasting is compared and analyzed. On this premise, the blast hole layout is refined further, the number of blast holes is reduced, and the optimal blasting scheme is determined. The results show that the coincidence degree of fracture area increases as the overdepth coefficient increases, and the blast hole utilization rate initially increases and then decreases as the overdepth coefficient increases, between 0.17 and 0.22, causing the blast hole utilization rate to the peak. This theory proposes a novel approach to increasing the blast hole utilization rate. When the depth of the overdepth is 400 mm, The blasting energy is primarily used to create a crack area around the cut hole, which provides enough free surface for the subsequent central hole and auxiliary hole blasting, reduces the difficulty of rock breaking, increases the volume of the blasting chamber, and facilitates subsequent rock throwing. Simultaneously, the effective stress of each measuring point decays slowly with time, the average stress is higher, and the tensile fracture effect of the stress wave on the surrounding rocks increases and prolongs, creating a complete and even rock mass fracture. The blast hole utilization rate reaches the maximum of 95.2%, the bulk rate and explosive unit consumption are significantly reduced, the rate of half-hole mark rate is significantly increased, and the road construction quality is good. It demonstrates that ultra-deep blasting can enhance not only the blast hole utilization rate but also the blasting impact and road construction quality, which has some guiding significance for the parameter optimization of rocky road drilling and blasting construction.

     

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