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掏槽孔超深深度對爆破效果的影響

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

  • 摘要: 煤礦巖巷鉆爆施工中,速度的關鍵在于掏槽。隨著巖巷掘進工程量不斷增大,雖然炮孔深度逐漸增大,但是掏槽孔超出普通孔的長度并沒有改變,基本保持在200 mm及以下。針對掏槽孔超深與炮孔利用率這一問題,本文在超深系數η的基礎上,引入裂隙區重合度φ的概念,利用數學建模方法,分析了不同超深深度爆破時的巖石應力狀態,建立了超深深度及巖石碎脹系數之間的關系,并確定了掏槽槽腔主要參數的計算公式及取值范圍,發現存在最優掏槽孔超深系數η和裂隙區重合度φ,使得炮眼利用率最高。利用LS-DYNA數值模擬分析了掏槽孔超深爆破時爆炸應力波的傳播規律和孔底巖石的受力特征,并比較了200、300、400和500 mm不同超深深度的應力波強度變化特征并應用于巖巷掘進現場,對比了超深爆破方案和普通爆破方案的單循環進尺、炮孔利用率、眼痕率及大塊率等爆破效果指標。結果表明,當超深深度為400 mm時,炸藥爆破能量充分用于破巖,能量利用率最高,爆破后形成重疊的裂隙區,增大了后續爆破的自由面,提高了爆破破巖的效率,對巖巷鉆爆法施工的參數優化有一定的指導意義。

     

    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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