Controlled Blasting in Tunneling: Techniques and Explosives Selection

Nepal, with its rocky topography and rapidly growing infrastructure needs, has seen a significant rise in tunneling projects, particularly for hydropower, road tunnels, and water supply systems. Given the country’s mountainous terrain and complex geology, controlled blasting has become a critical method for safe and efficient tunnel excavation. In various underground projects, blasting must be carried out with precision to ensure structural stability, protect surrounding environments, and minimize risk to workers and nearby communities. Therefore, controlled blasting, is not only a technical necessity but also a strategic choice in Nepal’s challenging tunneling environment.

The process of controlled blasting in Nepal starts with a detailed geological and geotechnical investigation. Nepal’s geology is diverse, consisting of hard rocks like granite in the Higher Himalayas, medium-strength rocks such as limestone in the mid-hills, and weaker formations in some regions. This geological variability makes site-specific blast design essential. Engineers drill a series of holes in specific patterns, cut holes in the center to initiate breakage, lifters at the bottom to break floor rock, and perimeter holes to define tunnel boundaries. The placement and spacing of these holes are optimized to match the rock strength and structure, minimizing overbreak and ensuring a smooth tunnel profile.

Key Techniques in Controlled Blasting for Tunnels

1. Smooth Blasting – Used for creating stable tunnel walls by drilling closely spaced holes with light explosive charges.
2. Pre-Splitting – Done before the main blast to create a fracture plane that helps control overbreak.
3. Cushion Blasting – Similar to smooth blasting but used at the tunnel perimeter after excavation.
4. Delay Blasting – Uses millisecond delays to sequence explosions, reducing ground vibrations.

The choice of explosives plays a critical role in the success of controlled blasting and must be tailored to the type of rock being excavated. In hard and massive rocks such as granite or basalt, high-energy explosives like emulsions or ANFO (Ammonium Nitrate Fuel Oil) are commonly used due to their high detonation velocity and energy output. Also, one of the most significant advancements in controlled blasting in recent years in Nepal’s tunneling industry, is the adoption of electronic detonators (Eds). These devices represent a major improvement over traditional initiation systems such as non-electric (NONEL)  or electric caps, providing millisecond-level precision, improved safety, and enhanced control over blast outcomes. The accuracy that electronic detonators provide is extremely beneficial for Nepal’s complicated geology. The use of modern blasting techniques support systems is crucial for maintaining tunnel stability during and after excavation.

Control blasting is crucial in Nepal’s tunneling industry, given the nation’s growing need for infrastructure, especially for urban utilities and hydropower development. Controlled blasting in Nepal’s tunneling projects requires a deep understanding of rock mechanics and explosive properties. By selecting the right explosives—such as ANFO for soft rocks and dynamites for hard granites—and employing techniques like smooth blasting and delay sequencing, engineers can ensure safe and efficient tunnel excavation. With proper planning and execution, Nepal’s ambitious hydropower and road tunnel projects can overcome geological challenges while minimizing environmental and structural risks.