Controlled Blasting

Controlled blasting refers to planned blasting techniques used in underground and surface excavation works to break rocks in a desired manner while minimizing environmental impacts. This technique plays a crucial role in areas such as tunnel construction, dams, highways, quarries, and mining operations, ensuring both the preservation of excavation geometry and safety. Controlled blasting methods are designed to protect the strength of surrounding rocks and the stability of slopes, as opposed to random and aggressive demolition.

Visual of Controlled Blasting Example(AA)

Purpose and Importance of Controlled Blasting

The primary goal of controlled blasting methods is to limit environmental impacts such as vibrations, rock ejection, excessive excavation, gas emissions, and noise caused by the blasting process. Particularly when blasting near structures or natural formations, controlled techniques are used to avoid triggering geological discontinuities and prevent the destruction of rock outside the excavation line.

Controlled blasting can also reduce the need for reinforcement, providing more cost-effective and longer-lasting solutions for engineering structures. The smooth and stable blasting surfaces lead to less use of support elements like sprayed concrete and piles.

Methods

Controlled blasting techniques are primarily divided into three groups:

Line Drilling

Holes drilled along the excavation boundaries, without explosives, at close intervals, create a weak plane that allows shock waves to reflect. This limits blasting energy and prevents cracks from extending beyond the excavation line. However, this method has disadvantages, such as high drilling costs and low efficiency in non-homogeneous rocks.

Smooth Blasting

Low-density explosives are placed in holes drilled at close intervals along the excavation line and detonated later than the production holes. This prevents damage to the surrounding rock outside the excavation line. It is commonly used in tunnel blasting. Precise drilling is required to avoid negative outcomes from hole deviations.

Presplitting

Before the production blast, closely spaced holes near the excavation boundary are lightly charged to create a fracture plane. This plane prevents radial cracks from the production blast from passing through, ensuring a smooth and durable excavation surface. It is often preferred in open-pit mines where slope stability is critical.

Blasting Design and Parameters

Success in controlled blasting depends on correctly determining parameters such as hole diameter, burden distance, hole spacing, explosive quantity, and hole inclination. For example, the Olofsson method provides mathematical formulas to determine the maximum burden distance based on the type of explosive and hole diameter. These formulas also account for factors such as rock constant (specific charge) and hole inclination correction factor.

Key Design Elements

• Bench Height (K): Ensures the blast is directed downward.
• Burden Distance (B): The distance between the hole and the free surface. According to Olofsson, this should be between 25-40 times the hole diameter.
• Bottom Charge and Column Charge: Stronger explosives should be used at the bottom, while lighter ones are recommended for the column.
• Compaction Length (h₀): Necessary to prevent gas escape and direct energy to the rock.

Cost and Optimization

Although controlled blasting may appear expensive due to high explosive costs, it can reduce overall operational costs by increasing efficiency in crushing, screening, and transportation processes.

If explosive consumption per unit (kg/m³) is not properly optimized, the amount of overburden (rock that needs to be blasted a second time) increases, leading to blockages in crushers and delays in loading and transportation.

In applications in limestone and granite quarries, the compatibility of blast velocities of different explosives, such as gelignite and ANFO, directly affects the fragmentation quality. Therefore, controlled blasting is considered not only a method for controlling environmental impact but also a tool for economic optimization.

Legal and Safety Aspects

The use of explosives in Turkey is strictly regulated under Regulation No. 87/12028 and Article 174 of the Turkish Penal Code. A license is required for the purchase, storage, transportation, and use of explosives. The firing personnel must hold an authorization certificate. The amount and type of explosives used for each blast must be recorded separately, and "consumption statements" must be prepared.

Controlled blasting has become an indispensable part of modern engineering and mining practices. This method ensures that only the rock within the target excavation boundaries is effectively broken, while also preventing environmental and structural damage. Scientific and careful determination of parameters such as drilling geometry, explosive selection, and firing sequence is crucial for the success of controlled blasting.