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3.10.2. Rock Blasting Theory

GENERAL

The major objectives of blasting are fragmentation and rock displacement. The variables that affect blasting are:

• Rockmass properties
• Explosive properties
• Blast geometry, angles of the blastholes towards free face
• Initiation

Numerous geological factors affect blasting operations. Though they are out of the blasteracute;s control, he may set values on controllable variables so that the desired rock fragmentation and displacement can be safely achieved.

The selection of explosives must not be underestimated. However, the characteristics of the rock mass are more significant in controlling the breakage and vibrations than the characteristics of the explosives used.

In contrast to rock and explosive properties, blast geometry and initiation include a range of variables that can be controlled by the operator. Optimizing blasting performance requires a clear understanding of their significance.

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After the round has been detonated, it is impossible to control. Therefore, the blaster must take extreme care in planning the blast. In order to successfully accomplish the task, he must use good judgement in matching the blasting requirements, methods and materials.

Rock is affected by a detonation in three principal stages. First, a shock wave released by the detonation passes through the rock mass at a (detonation) velocity of 3000 m/s - 6000 m/s, depending mainly on the rock geology. This velocity corresponds to 0.15 - 0.3 milliseconds per meter of burden. The rock is stressed by compression (FIGURE 3.10.-20.). The shock wave does not break the rock, but crushes the blasthole walls and

After reflecting from free faces, the shock waves expose the rock to tensile forces. Shock waves are reflected from bench faces or joints in the rock. Experiments have shown that the velocity of the shock wave after reflection is 500 m/s - 2000 m/s or 0.5 - 2.0 milliseconds per meter of burden. Tensile forces cause small primary, often radial, cracks that extend from the center of the hole (FIGURE 3.10.-21.).

Upon detonation, large quantities of high-pressure

expanding gases spread into the primary cracks

(FIGURE 3.10.-22.). The cracks expand, the rockrsquo;s free surface moves forward, pressure is unloaded and tension increases in the primary cracks. The primary cracks then expand to the surface which promotes the complete loosening of the rock. The burden is consequently torn off.

High-speed photographs taken during experiments show the relationship between the burden, specific charging and the speed of rock movement during blasting. Bench blasts are usually designed with the speed of 10 - 30 m/s, or in other words, FIGURE 3.10.-22. Gas expansion.

30 - 100 milli-seconds per meter of movement.

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The following formula gives the movement speed of the torn-off burden as a function of rock hardness, burden distance and charging per meter of hole:

V0 = (K/V1.17)I0.39

where v0 = speed of movement (m/s)

K = constant of rock hardness (soft rock = 15, hard rock = 33)

V = burden (m)

I = charging per meter (kg/m)

The explosive reaction in the blasthole is very fast and its power is considered completed when blasthole volume has expanded to 10 times its original volume which takes approx. 5 ms.

The graph in FIGURE 3.10.-23 shows how the expansion of the blasthole is related to time.

1. Shock wave initiation in rock crushing. The blasthole expands to double its original volume (2V0). The blasthole remains at this volume for a relatively long time (0.1 to 0.4 ms) before radial cracks begin to open.
2. In addition to natural cracks, new cracks are formed mainly by interaction between thestress field around the blasthole and tensile stress formed by reflection of the outgoing shock wave at the free face. Reaction products expand from blasthole (volume now quadrupled) into the cracks. Fragmentation begins.
3. Gas expands further and accelerates the rock mass.

FIGURE 3.10.-23. Blasthole expansion in relation to time.

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3.10.2。岩石爆破理论

一般爆破的主要目的是破碎和岩石位移。影响爆破的变量有：

-Rockmass属性

-爆炸特性

-爆破几何形状，炮眼朝向自由面的角度

-启动

许多地质因素影响爆破作业。尽管它们不受抛丸器的控制，但他可以在可控变量上设置值，以便可以安全地实现所需的岩石碎裂和位移。

爆炸物的选择一定不能低估。但是，岩体的特征比所用炸药的特征在控制破裂和振动方面更为重要。

与岩石和爆炸物的特性相反，爆炸的几何形状和起爆包括操作人员可以控制的一系列变量。优化爆破性能需要清楚了解其重要性。

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产生微观节理，有助于在第二阶段破碎和切割岩石。

图3.10.-20。岩石压缩

该弹被引爆后，就无法控制了。因此，抛丸器在计划抛丸时必须格外小心。为了成功完成任务，他必须运用良好的判断力来匹配爆破要求，方法和材料。

岩石在三个主要阶段受到爆炸的影响。首先，由爆震释放的冲击波以（爆炸）速度3000 m / s-6000 m / s穿过岩体，这主要取决于岩石的地质情况。该速度对应于每米负荷0.15-0.3毫秒。岩石受到压缩应力（图3.10.-20。）。冲击波不会破坏岩石，但会压碎爆破孔壁并

从自由面反射后，冲击波使岩石承受拉力。冲击波从岩石的工作台面或接缝反射出来。实验表明，反射后冲击波的速度为500 m / s-2000 m / s或每米负荷0.5-2.0毫秒。拉伸力会引起小的，通常是径向的裂纹，这些裂纹从孔的中心开始延伸（图3.10.-21。）。

爆炸时，大量高压

形成气体。通过快速放热，

图3.10.-21。自由面孔的冲击波反射。

膨胀的气体扩散到主要裂缝中

（图3.10.-22。）。裂纹扩展，岩石的自由表面向前移动，压力释放，初级裂纹的张力增加。然后，初级裂纹扩展到表面，这促进了岩石的完全松弛。结果，负担被扯掉了。

实验期间拍摄的高速照片显示了爆破过程中的负担，比电荷和岩石移动速度之间的关系。台式冲击波的设计速度通常为10-30 m / s，即

图3.10.-22。气体膨胀。

每米运动30到100毫秒。

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以下公式给出了被撕开的重物的移动速度与岩石硬度，重物距离和每米孔的装料量的关系：

V0 =（K

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