空孔直径对有围压直眼掏槽爆破破碎效果的影响

Influence of diameter of empty hole on the fragmentation effect of parallel cut blasting under confining pressure

掏槽爆破是井巷爆破掘进的关键技术,高围压对掏槽爆破效果有明显的抑制效果,而空孔对于提高掏槽爆破效率具有重要意义,但目前相关研究并不充分。为研究中空孔直径对围压作用下掏槽爆破破碎效果的影响,制作边长为600 mm、砂胶质量比为2∶1的立方体水泥砂浆试块,并通过电液伺服加载系统对试块施加双向等围压,进行直眼掏槽爆破水泥砂浆相似模型试验。对爆后爆破块度进行筛分统计分析,分析研究了不同中空孔直径下模型碎块块度分布、平均粒径,通过分形维数表征碎块分形特征,量化分析了碎块破碎程度。采用ANSYS/LS–DYNA软件基于试验模型参数建立了数值模型,分析了不同空孔直径时不同时刻的应力云图。研究结果表明:炮孔装药量分别为2 g和3 g时,中空孔直径为24 mm和16 mm的模型碎块分形维数最大,此时碎块粒径主要集中19~75 mm的中部区间,且此时碎块总质量最大,分别为3.128、3.615 kg,空孔直径不同时,空孔附近产生的应力集中效应与反射拉伸波效果不同,使得掏槽爆破破碎效果不同,适宜的空孔直径能够有效利用空孔效应,空孔附近应力波峰值和作用范围较大,应力波作用时间较长,因此破碎效果较好;空孔直径过小,空孔附近应力较小,空孔直径过大时,应力波由空孔溢出,应力集中叠加后的压应力较小,且拉伸应力作用区域较小,空孔直径过大或过小都会使大块度碎块占比较高;装药量为3 g时,空孔直径32 mm与16 mm模型碎块的分形维数差值大于16 mm与无空孔模型碎块分形维数的差值,说明当空孔直径过大时对碎岩块度的影响更大;空孔直径同为16 mm时,3 g装药量模型的碎块平均粒径小于2 g装药量模型,分形维数及碎块总质量大于2 g装药量模型试块,说明当空孔直径相同时增加装药量可以提高岩石的破碎度及槽腔体积。

Cut blasting is the key technology for roadway blasting excavation.High confining pressure has obvious inhibition effect on cut blasting effect,while empty hole is of great significance to improve cut blasting efficiency,but the relevant research is not sufficient so far.To study the crushing effect of the cut blasting with different empty hole diameters under the confining pressure,cubic cement mortar test blocks whose side length was 600 mm were made with sand cement ratio of 2:1.The test blocks were subjected to equal bi-axial confining pressure through an electro-hydraulic servo loading system,and the parallel cut blasting cement mortar physical model test was carried out.After the blasting fragmentation was screened and statistically analyzed,the fragmentation distribution and average particle size of model fragments under different empty hole diameters were analyzed and investigated.With fractal features of fragments characterized by fractal dimension,the fragmentation degree was quantitatively analyzed.ANSYS/LS–DYNA software was used to establish numerical models based on the parameters of the test model,and the stress contour at different times with different hole diameters was analyzed.The research result shows that,when two empty holes are charged with different charge of 2 g and 3 g,respectively,the maximum fractal dimension of the model fragment can be attained with empty holes in diameter of 24 mm and 16 mm,respectively,with the particle size of the fragment mainly concentrated in the middle segment between 19 to 75 mm,and the largest total mass of the fragment is 3.128 kg and 3.615 kg,respectively;When the sizes of empty holes are different,the stress concentration effect and the reflected tensile wave produced near the empty hole are also different,which brings the difference of cut blasting fragmentation effect and can effectively benefit from the empty hole effect.The peak value and action range of stress wave near the empty hole are bigger,with a long action time,suggesting a better crushing effect;the diameter of the empty hole is too small,the stress around the empty hole is small.An oversized empty hole will lead to the overflow of the stress wave from the hole.The compressive stress is small after the superposition of stress concentration,and the action area of tensile stress is also small.The proportion of large rock pieces will be high with extremely large or small empty hole.When charged with 3 g,the fractal dimension difference between empty hole model fragments of 32 mm and 16 mm is greater than the difference of model fragments between 16 mm and without empty hole,indicating that the influence on the fragmentation of rock is greater when the empty hole diameter is too large.When the empty hole diameter is the same as 16 mm,the average particle size of the fragments in the model charged with 3 g is less than that in the model charged with 2 g,with the greater fractal dimension and total mass of the fragments than that in the test model charged with 2 g.This shows that an increased charge can contribute to rock fragmentation and the volume of the cut cavity with the same diameter of empty holes.