How does geological structure (joints, faults, bedding) affect blast design and energy distribution?

In the fields of mining and civil engineering, the efficiency of rock fragmentation is not solely a product of explosive power. Rather, it is fundamentally governed by the interplay between explosive energy and the geological structure of the rock mass, specifically its joints, faults, and bedding planes (Gao, 2023). While controllable parameters like burden, spacing, and stemming are vital, the “uncontrollable” geological variables dictate how energy is distributed and dissipated within the medium (Saadoun et al., 2024).

Influence of joints on energy distribution

Joints, natural fractures in rock, act as primary discontinuities that interrupt the propagation of stress waves. When an explosive detonates, it generates a high-pressure shockwave that transitions into a stress wave. At a joint interface, this wave undergoes complex transmission, reflection, and diffraction (Gao, 2023).

• Wave reflection and attenuation: joints can act as barriers that arrest stress waves. If a joint is filled with soft, compressible material, it absorbs a significant portion of the energy, reducing the intensity of the transmitted wave and leading to poor fragmentation on the far side of the joint (Investigation of Rock Joint and Fracture Influence on Delayed Blasting Performance, 2023).
• Fragmentation enhancement: conversely, existing joints can be beneficial. Research indicates that jointed blocks often produce finer median fragmentation than intact rock because the stress waves propagate inherent cracks until they intersect with the free face (Gao, 2023). Optimal fragmentation typically occurs when joint sets are inclined at specific angles, such as 60°, which enhances wave reflection toward the free surface (Small-scale experimental and numerical simulation of blasting in jointed rock-like materials under varied joint and explosive conditions, 2025).

The role of faults in blast stability and vibration

Faults are larger-scale discontinuities that significantly complicate blast design. Unlike minor joints, faults often contain “gouge” or highly fractured material that can lead to hazardous energy venting.

• Energy escape and muckpile shape: if a borehole intersects a fault, the high-pressure explosion gases may escape prematurely through the fault zone. This leads to a loss of heave energy, resulting in a “frozen” or poorly displaced muckpile (The Influence of Explosive and Rock Mass Properties on Blast Damage in a Single-Hole Blasting, 2024).
• Vibration anisotropy: fault zones act as filters for blast-induced vibrations. Studies have shown that vibration velocities measured behind a fault zone are significantly different from those in non-faulted zones due to the reflection of Rayleigh and Love waves (Gonen, 2022). This requires engineers to adjust delay patterns to prevent damage to nearby structures or pit slopes.

Bedding planes and anisotropy

Bedding planes, the layers in sedimentary rock, introduce anisotropy into the blasting process. The orientation of these layers relative to the blast face determines the ease of rock breakage.

• Fragmentation and overbreak: bedding planes serve as weak surfaces that guide crack propagation. If the bedding is parallel to the bench face, the rock may “slab” off in large, flat blocks. Conversely, drilling perpendicular to prominent bedding sets generally produces a more uniform fragmentation curve (Evaluation of the Amount of Boulder in the Pile as a Result of Blasting Patlatma Sonucu Oluşan Yığın İçindeki Patar Miktar, 2025).
• Energy utilization: in thin-bedded limestone, for example, the rock’s load-bearing capacity is lower, making it more susceptible to collapse and overbreak (Gao, 2023).

Optimizing blast design for complex geology

To mitigate the negative effects of geological discontinuities, engineers must adapt the powder factor (specific charge) and charge structure.

Ultimately, successful blast design requires a shift from viewing rock as a homogeneous solid to treating it as a heterogeneous system. By matching explosive properties (like Velocity of Detonation) to the impedance and structural orientation of the rock mass, operators can maximize energy utilization and reduce the costs of downstream processes like crushing and hauling (Zhu & Zhou, 2024).

References

Gao, P. (2023). Rock fragmentation size distribution control in blasting: a case study of blasting mining in Changjiu Shenshan limestone mine. Frontiers in Materials, 10. https://doi.org/10.3389/fmats.2023.1330354

Gonen, A. (2022). Investigation of Fault Effect on Blast-Induced Vibration. Applied Sciences, 12(5), 2278. https://doi.org/10.3390/app12052278

Investigation of Rock Joint and Fracture Influence on Delayed Blasting Performance. (2023). MDPI. https://www.mdpi.com/2076-3417/13/18/10275

Saadoun, A., Boukarm, R., Fredj, M., Menacer, K., Boudjellal, D., Hafsaoui, A., & Yilmaz, I. (2024). Optimal Blast Design Considering the Effects of Geometric Blasting Parameters on Rock Fragmentation: A Case Study. ARPHA Proceedings, 1, 136–146. https://doi.org/10.3897/ap.7.e0136

The Influence of Explosive and Rock Mass Properties on Blast Damage in a Single-Hole Blasting. (2024). Preprints.org. https://doi.org/10.20944/preprints202402.0351.v1

Zhu, Z., & Zhou, Z. (2024). Experimental Study for the Matching of Explosives and Rocks Based on Rock Hydrophysical Properties. Water, 16(13), 1807. https://doi.org/10.3390/w16131807

Small-scale experimental and numerical simulation of blasting in jointed rock-like materials under varied joint and explosive conditions. (2025). PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC12571288/

Evaluation of the Amount of Boulder in the Pile as a Result of Blasting Patlatma Sonucu Oluşan Yığın İçindeki Patar Miktar. (2025). DergiPark. https://dergipark.org.tr/tr/download/article-file/4914271