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

Literature Overview

This paper, published in Engineering Blasting (2025, Vol. 31, No. 1, pp. 89–94), authored by Li Yaru, Sun Jinshan, Dong Qian, Nie Senlin, and Ming Weihua from Jianghan University and the State Key Laboratory of Fine Blasting, investigates the detonation performance of emulsion explosives under confinement conditions simulated by high-strength seamless steel pipes. The research is funded by the Jianghan University First-Class Discipline Construction Major Special Fund (2023XKZ042), the National Key R&D Program (2021YFC3100804), and the National Natural Science Foundation (52108368). The study addresses the critical question of whether small-diameter emulsion explosives can achieve stable detonation under strong lateral confinement, which is essential for precision blasting applications in tunnel construction and similar operations.

Core Technical Content

The research employs high-strength seamless steel pipes of three different diameters (11 mm, 16 mm, and 20 mm) to simulate the lateral confinement conditions encountered in tunnel perimeter blast holes. A five-stage detonation velocity measuring device is used to record the detonation wave propagation process. The study compares detonation velocities under steel pipe confinement with those under unconstrained conditions for three different charge diameters.

Detonation Velocity Results Under Steel Pipe Confinement

The results demonstrate that emulsion explosives can achieve stable detonation under confinement by 11 mm, 16 mm, and 20 mm steel pipes, with detonation velocity increasing with pipe diameter. The 20 mm confined charge achieves a detonation velocity of 4532.58 m/s, which is comparable to that of a 32 mm industrial charge without confinement.

Critical Findings on Confinement Effects

Under unconstrained conditions, severe lateral energy loss occurs, and charges with diameters of 20 mm or less fail to detonate entirely. This stark contrast between confined and unconstrained behavior highlights the critical role of lateral confinement in maintaining detonation stability for small-diameter charges. The steel pipe acts as a confinement vessel that prevents lateral energy dissipation, thereby sustaining the detonation wave front.

Density Effects Under 11 mm Pipe Confinement

Under 11 mm steel pipe confinement, the detonation velocity of the charge decreases linearly with increasing charge density. The linear fitting correlation coefficient reaches 0.97901, indicating an excellent linear relationship. This finding is significant because it demonstrates that detonation energy release rate can be controlled by adjusting charge density, providing a mechanism for precision control of blasting effects.

Engineering Practice Implications

The findings of this research have direct relevance to tunnel construction and mining operations where small-diameter perimeter holes are used for smooth wall blasting (also known as smooth blasting or pre-split blasting). The ability to achieve stable detonation in small-diameter charges under steel pipe confinement opens up new possibilities for precision blasting with reduced overbreak and improved rock face quality.

Application to Smooth Wall Blasting

In smooth wall blasting operations, the perimeter holes are drilled close to the final tunnel profile, and the goal is to fracture the rock along the desired boundary without excessive damage to the surrounding rock mass. The key challenge is ensuring reliable detonation of small-diameter charges while controlling the energy release to avoid overbreak. This research demonstrates that:

• Small-diameter emulsion explosives (11–20 mm) can achieve stable detonation when confined by high-strength steel pipes, addressing the reliability concern for small charges.
• The detonation velocity can be controlled through charge density adjustment, enabling tuning of the energy release rate to match specific rock conditions and desired fracture patterns.
• The 20 mm confined charge achieves detonation velocities comparable to conventional 32 mm charges, suggesting that smaller charges can be used with appropriate confinement to achieve similar blasting effects while reducing hole diameter and drilling costs.

Steel Pipe Selection for Confinement Applications

From a materials and fabrication perspective, the selection of high-strength seamless steel pipes for confinement applications requires consideration of several factors:

• Pipe strength: The pipe must withstand the detonation pressure without rupture, which requires high yield and ultimate tensile strength.
• Pipe geometry: Diameter and wall thickness must be selected to provide adequate confinement while accommodating the charge diameter and leaving sufficient clearance for detonation wave propagation.
• Pipe quality: Surface defects, thickness variations, or weld discontinuities could compromise confinement integrity and lead to premature failure.
• Pipe compatibility: The pipe material must be compatible with the emulsion explosive composition to avoid any adverse chemical interactions.

FMEA Analysis for Confinement-Based Blasting

Applying Failure Mode and Effects Analysis to this application:

• Pipe rupture: If the steel pipe fails under detonation pressure, the confinement is lost, leading to energy dissipation and potential detonation failure. Mitigation requires careful pipe strength selection and quality inspection.
• Charge density variation: Inconsistent charge density leads to variable detonation velocities and unpredictable blasting results. Mitigation requires precise charge formulation and controlled charging procedures.
• Hole deviation: If the steel pipe is not properly centered in the blast hole, asymmetric confinement can lead to directional energy bias and uneven rock fracture. Mitigation requires accurate hole drilling and pipe placement.

Study Insights and Independent Reflection

This research addresses an important practical problem in precision blasting technology. The demonstration that small-diameter emulsion explosives can achieve stable detonation under steel pipe confinement is a significant finding that expands the range of viable charge configurations for controlled blasting operations. The linear relationship between charge density and detonation velocity under confinement provides a straightforward mechanism for energy control, which is highly valuable for engineers seeking to optimize blasting parameters.

From my experience with steel pipe specifications and quality standards, I note that the use of high-strength seamless steel pipes for this application is appropriate, as seamless pipes provide uniform mechanical properties without the potential weak points associated with welded seams. The pipe grades and specifications used should be documented to ensure traceability and consistency in future applications.

One aspect that I would recommend for further investigation is the effect of pipe wall thickness on detonation performance. While the study varies pipe diameter, the wall thickness effect on confinement effectiveness and energy transmission is not explicitly examined. Additionally, the study could benefit from examining the effect of different steel pipe grades, as the mechanical properties of the pipe material may influence the confinement effectiveness and detonation wave characteristics.

The research also raises interesting questions about the interaction between the detonation wave and the steel pipe material. The steel pipe undergoes significant deformation and potentially local plasticization during detonation, and understanding this interaction could lead to improved pipe design for confinement applications. Metallographic examination of the pipe material after detonation events could reveal the extent of plastic deformation, phase transformations, and potential damage mechanisms.

Overall, this study provides valuable data for the development of precision blasting technologies using small-diameter confined charges, and the findings should be considered in the design and implementation of smooth wall blasting operations in tunnel construction and mining applications.