Fundamentals of Blasting Engineering: Rock Classification, Initiation Technology, and Surface Blasting

Introduction

The effectiveness of blasting operations is influenced by both engineering geological conditions and design implementation. Since blasting is conducted directly within rock masses, factors such as rock type, hardness, and rock mass integrity determine the difficulty of blasting. Understanding the physical and mechanical properties of rocks and rock masses, and designing blasting parameters accordingly, can improve blasting efficiency and reduce safety risks.

Rock Properties and Classification

Distinction Between Rock and Rock Mass

In engineering blasting, it is important to distinguish between rock and rock mass. Rock refers to a natural aggregate composed of one or more minerals or rock fragments. A homogeneous rock without significant weak planes is called a rock block and can be used to represent the corresponding rock type. Rock mass, on the other hand, refers to the combination of rock blocks under natural geological conditions, intersected by weak structural planes such as joints and fissures. The strength of a rock mass is generally lower than that of intact rock. The structure, joints, and fractures of a rock mass have significant impacts on blasting safety and overall stability.

Classification of Rocks

According to their origin, rocks can be divided into three main categories.

• Igneous rocks (magmatic rocks): Formed by the cooling and solidification of magma. Those solidified underground are intrusive rocks, while those erupted onto the surface are volcanic rocks.
• Sedimentary rocks: Formed from weathering, dissolution, transportation, and deposition processes, later consolidated under normal temperature and pressure.
• Metamorphic rocks: Formed from pre-existing igneous or sedimentary rocks that underwent recrystallization or structural transformation under high temperature, high pressure, or other metamorphic conditions.

Unconsolidated deposits: Loose accumulations formed by weathering and sedimentation that have not yet lithified into rock.

Understanding the rock type and its strength is essential for selecting suitable blasting methods and determining the appropriate powder factor.

Initiation Technology

Common Initiation Methods

Blasting designs employ several initiation methods. According to the mode of detonator initiation, these can be categorized into safety fuse initiation, electric detonator initiation, and shock tube detonator initiation. Additionally, there are wireless initiation systems (e.g., electromagnetic or acoustic), which essentially belong to the electric initiation category.

• Safety fuse initiation: Uses a safety fuse to ignite a plain detonator. Advantages: simple structure, low cost. Disadvantages: must be ignited at the working face, poor safety, and inaccurate timing. In China, the production and use of civil safety-fuse detonators were discontinued in 2008.
• Shock tube initiation: Uses a shock tube to transmit a detonation wave to the detonator. Advantages: immune to electromagnetic interference, safe and reliable. Applications: tunneling, surface deep-hole blasting, and demolition projects.
• Electric initiation: Uses an electric firing system to ignite detonators, allowing remote initiation and millisecond delay control. Advantages: electrical resistance and circuit continuity can be measured before firing, ensuring initiation reliability. Disadvantages: susceptible to stray current, static electricity, or lightning; circuit layout is complex in large-scale blasting.

Electric Initiation System Parameters

In an electric detonator system, the total resistance consists of bridge wire resistance and leg wire resistance. Chinese industrial electric detonators typically use nickel-chromium alloy bridge wires with resistance deviation ≤ 0.8 Ω. Safety current can pass through a detonator for 5 minutes without initiation (≥ 0.20 A). Electrical testing of the blasting network must use a special continuity tester or blasting ohmmeter; the test current shall not exceed 30 mA.

Surface Blasting Technology

Design of Deep-Hole Bench Blasting

Deep-hole bench blasting is widely used in surface mining, railway, highway, and hydropower projects. It typically applies to blastholes with a diameter > 50 mm and depth > 5 m. The design must determine the following key parameters:

• Bench height (H): Vertical height of the bench
• Burden (W₁): Distance from the bottom of the front row holes to the free face
• Hole depth (L): Total drilling length (sum of charge length and tamping length)
• Charge length (l₁) and tamping length (l₂) : Length of explosive column and length of tamping material
• Hole spacing (a): Distance between adjacent holes in the same row
• Row spacing (b): Distance between adjacent rows of holes
• Slope angle (α): Angle between the bench face and the horizontal plane

Correct determination of these parameters ensures optimal blasting fragmentation and slope stability.

Comparison Between Vertical and Inclined Holes

Deep-hole bench blasting can employ vertical or inclined holes. Vertical holes are applicable to various geological conditions, offering higher drilling efficiency, but tend to produce coarse fragmentation and leave toe burdens, leading to poor slope stability. Inclined holes are suitable for small and medium quarries, decorative stone mining, and soft-rock excavation. They yield more uniform fragmentation and stable slopes but are technically more demanding and unsuitable for hardrock.

Drilling Patterns

Drilling layouts for deep-hole bench blasting include single-row and multi-row patterns. Multi-row layouts can adopt square, rectangular, or triangular arrangements: In the square pattern, burden and spacing are equal. In the rectangular pattern, the burden is smaller than the spacing. In the triangular pattern, the burden may be equal to or smaller than the spacing; this layout often requires supplementary holes to achieve uniform blasting.

Conclusion

This document introduces the fundamental knowledge of blasting engineering, including rock classification, initiation technology, and principles of surface blasting design. Understanding rock characteristics and initiation methods is crucial for designing safe and efficient blasting operations.