Detonation Velocity Characteristics of Small-Diameter Emulsion Explosives Under High-Strength Steel Pipe Confinement

Literature Overview

This paper by Li Yaru and colleagues from Jianghan University's State Key Laboratory of Fine Blasting, Hubei Provincial Key Laboratory of Blasting Engineering, and Hubei (Wuhan) Institute of Explosion and Blasting Technology investigates the detonation performance of small-diameter emulsion explosives under the confinement of high-strength seamless steel pipes. Published in Engineering Blasting (Volume 31, Issue 1, 2025, pages 89-94), the study is supported by multiple funding sources including the National Key R&D Program (2021YFC3100804) and the National Natural Science Foundation (52108368). The research addresses a critical practical challenge in tunnel blasting operations where small-diameter peripheral charges require reliable detonation under confined conditions.

Core Technical Approach

The experimental methodology employed high-strength seamless steel pipes to simulate the lateral confinement conditions encountered in tunnel drill-and-blast construction of peripheral blast holes. A five-point detonation velocity recorder was used to capture the detonation wave propagation process, providing detailed measurements of detonation velocity across the charge length.

The study compared detonation performance under two conditions: steel pipe confinement and free (unconfined) conditions, across three charge diameters. Additionally, a dedicated investigation examined the influence of explosive density on detonation velocity within the smallest pipe diameter constraint.

Key Technical Parameters and Results

Technical Analysis of Confinement Effects

The fundamental principle underlying this research is that detonation requires sufficient lateral confinement to maintain the detonation wave stability. In free conditions, small-diameter charges suffer severe lateral energy losses through radial expansion of detonation gases, which cannot sustain the detonation front propagation. The seamless steel pipe provides the necessary lateral constraint to contain the detonation energy within the charge column.

The seamless steel pipe was selected as the confinement medium due to its uniform wall properties, absence of weld seams that could create weak points, and high tensile strength that prevents premature pipe failure during detonation. This simulates the actual rock confinement in peripheral blast holes, where the surrounding rock mass provides lateral support to the charge.

The finding that 20 mm pipe-confined charges achieve detonation velocities comparable to 32 mm free charges (4532.58 m/s) is practically significant. It demonstrates that small-diameter charges can achieve full detonation performance when properly confined, enabling their use in applications where large-diameter charges are impractical.

Density-Velocity Relationship Analysis

The inverse relationship between charge density and detonation velocity under 11 mm pipe confinement is counterintuitive at first glance but can be explained through detonation physics. Higher density emulsion explosives contain more explosive material per unit volume, but the confinement geometry limits the available expansion space. The increased mass per unit volume in a confined geometry creates higher internal pressure that can partially quench the detonation front, resulting in reduced propagation velocity.

The high correlation coefficient (0.97901) of the linear fit indicates a strong and predictable relationship, which has direct implications for charge design optimization. Engineers can calculate expected detonation velocities for specific density selections, enabling precise control of energy release rates for different blasting objectives.

Engineering Application Implications

Study Insights and Reflections

The research confirms a critical practical principle: small-diameter emulsion explosives can achieve reliable detonation when adequately confined, and this confinement need not be geological—it can be provided by engineered steel pipe structures. This finding opens new possibilities for precision blasting applications where energy control is paramount.

The ability to control detonation velocity through density adjustment within a fixed geometric constraint represents a powerful tool for blasting engineers. Rather than relying solely on charge diameter selection—which may be limited by hole diameter constraints—engineers can now fine-tune detonation performance through density optimization. This dual-variable control (diameter and density) provides significantly greater flexibility in matching explosive energy to specific fragmentation requirements.

From a steel pipe engineering perspective, the study highlights the importance of seamless pipe quality in explosive applications. The absence of weld seams ensures uniform confinement strength around the entire charge circumference, preventing localized failure that could compromise detonation stability. The high-strength seamless pipe specification is therefore not merely a cost consideration but a functional requirement for reliable performance.

Reference Value and Outlook

This study provides quantitative data and design guidance for the application of small-diameter emulsion explosives in confined blasting operations. The established relationships between pipe diameter, charge density, and detonation velocity can be incorporated into blasting design software for automated charge optimization. Future research should investigate the effects of different steel pipe grades on detonation performance, the influence of pipe wall thickness on energy containment, and the applicability of these findings to other explosive types beyond emulsion formulations. The methodology of using engineered confinement to achieve reliable detonation in small-diameter charges has potential applications beyond mining and tunneling, including precision demolition and controlled fragmentation in civil engineering.