隧道掏槽爆破中起爆点位置对爆炸能量传输的影响作用及其比选研究

为比较评价起爆点位置对隧道掏槽爆破效果的影响，分别基于一维等熵流爆轰理论和柱状药包爆炸应力场叠加模型，分析了柱状药包爆轰波传播的方向效应和时间效应，揭示了起爆位置对爆炸能量传输的影响作用机理；通过单孔爆破现场试验，对比分析了正向起爆、反向起爆和中点起爆等传统起爆方式下孔口岩体的破裂形态及地表爆破振动峰值，佐证了起爆位置对爆炸能量传输的影响作用规律；依次建立了普通单孔爆破和隧道掏槽爆破数值模型，模拟计算了正向起爆、反向起爆和中点起爆3种传统起爆方式下的炸药爆轰加载特征与爆破损伤演化规律，评价了传统起爆方式下掏槽爆破效果的优劣，并探讨了掏槽孔起爆方式的改进方案。研究结果表明：起爆位置的影响作用机理源于柱状药包爆轰波传播的方向效应和爆炸应力场叠加的时间效应，柱状药包起爆后爆轰产物和爆炸能量偏向于爆轰波传播的正向传输，其应力场也在爆轰波传播的正向叠加增强；试验结果显示，反向起爆时孔口岩体破裂与鼓包痕迹最为显著，中点起爆次之，而正向起爆最小；传统的反向起爆、正向起爆和中点起爆均有各自的利弊，反向起爆利于形成爆破漏斗，但易于造成根底，限制了掏槽爆破进尺，正向起爆虽有助于孔底岩体破碎，但容易在孔口形成大块，岩体抛掷效果也较差，中点起爆可兼顾孔口与孔底岩体的破碎，但孔中部岩体的破碎不充分，为此尝试提出了一种基于邻孔反向传爆的混合起爆方式，其结合了传统起爆方式的优点，且增强了邻孔之间的拉伸和剪切效应，岩体破碎较为均匀。

Study on Influence Law of Initiation Position on Transmission of Explosion Energy and Its Comparison and Selection in Tunnel Cutting Blasting

The present study aimed to compare and evaluate the influence of the initiation position on the blasting effect of tunnel cutting. At the first section, the direction and time effects of the detonation wave propagating along the cylindrical charge were analyzed using the one-dimensional isentropic flow detonation theory and the superposition model of blast stress field. As a result, the influence law of the initiation position on transmission of explosion energy was answered. Then, through an onsite single-hole blasting experiment, the fracture shape of orifice rock mass and surface peak particle velocity (PPV) under the traditional initiation mode such as direct (top), reverse (bottom), and mid-point initiations were compared and analyzed, thus demonstrating the influence law of initiation position on the transmission of explosion energy. At the third section, the explosion loading characteristics and damage evolution law under three traditional initiation modes(top, bottom, and midpoint initiations) was investigated via ordinary single-hole blasting and tunnel cutting blasting numerical simulation.The advantages and disadvantages of the cutting blasting effect under traditional initiation mode were also evaluated. Finally, the improvement of the initiation mode based on the regulation of explosion energy was studied. The results indicate that the acting mechanism of initiation position lies in the direction effect of the propagation of detonation wave and the time effect of the superposition of the blast stress field of the cylindrical charge. The detonation products and explosion energy tend to propagate through the forward direction of the detonation wave after the cylindrical charge is detonated. Besides, the blast stress field is also strengthened along the forward direction. The test results show that the crack and bulge trace of the orifice rock mass are the most evident under bottom initiation, followed by the midpoint initiation; the top initiation is the smallest. The traditional initiation modes, i.e., bottom, top, and midpoint, have their own advantages and disadvantages. The bottom initiation is beneficial for forming the blasting crater, but it easily causes rock toes at the hole-bottom, which restricts the excavation footage. Although the top initiation can strengthen the breakage of rock mass at the hole-bottom, large boulders might be formed at the hole-orifice, and the throwing effect of rock mass is notably poor. The midpoint initiation could balance the rock fragmentation at both the hole-orifice and hole-bottom; however, the fragmentation at the middle section is not enough. Subsequently, a combined initiation mode based on the opposite detonation of adjacent blast-holes was proposed. The new initiation mode not only inherits the advantages of traditional initiation modes, but enhances the tensile and shear effects between adjacent blast-holes, and the rock fragmentation is consequently more uniform.