Case Study: Effect of Stemming Length on Blast Fragmentation – Part 2 This part of this article evaluates a granite quarry blast introduced in Part 1 of my post (https://lnkd.in/efKgchFt), which consisted of two sections designed with different stemming lengths. The decision to adjust the stemming length was driven by the need for improved confinement, aiming to reduce excessive energy venting and mitigate poor fragmentation caused by energy loss. The first image illustrates the division of the blast: one section with a 1.8 m stemming length and the other with a 2.0 m stemming length. Each blast hole was drilled on a 2.7 m × 2.3 m pattern, and the stemming material used had a D80 size of 22 mm. Results show that while the 2.0 m stemming zone provided better confinement, it produced coarser fragments due to pre-existing geological fractures. These fracture observations and their influence on fragmentation were discussed in detail in the referenced article available here: https://lnkd.in/e7ytv28B The second application of the adjusted stemming length demonstrated both strong confinement and improved fragmentation. WipFrag was used to analyze each section independently, as shown in the attached images. The yellow pocket is the Quarry crusher compatibility, design on WipFrag for this quarry KPI sizes.

Effect of Stemming Length on Blast Fragmentation Stemming length plays a critical role in blast performance and the resulting rock fragmentation. The primary function of stemming is to confine explosive gases within the borehole long enough for the shock wave and gas energy to fully act on the surrounding rock mass. When stemming is optimized, more of the explosive energy is transferred into productive breakage rather than being lost as airblast, flyrock, or excessive vibration. 1. Under-Stemming (Too Short) When the stemming column is shorter than required: a. Loss of confinement leads to early venting of gases. b. Reduced energy utilization causes coarser fragmentation. c. Increased airblast and flyrock due to premature blowout. d. Higher variability in fragmentation, making downstream processes less stable. The lack of confinement prevents the explosive from fully fracturing the burden, often resulting in oversized boulders, uneven muckpiles, and inefficiencies in crushing and hauling. 2. Over-Stemming (Too Long) When the stemming column is longer than necessary: a. Energy is overly confined and may not generate adequate heave. b. Fragmentation becomes finer near the collar but may remain coarse at depth. c. Potential for poor throw and tight muckpiles if explosive energy cannot effectively mobilize the rock. d. Over-stemming can create a blast that breaks the collar region well but leaves deeper zones under-fragmented, affecting shovel diggability and crusher feed consistency. Evaluating Stemming Effect Using WipFrag for Continuous Improvement WipFrag offers a practical and data-driven way to assess how changes in stemming length influence fragmentation outcomes across multiple blasts. Because WipFrag is developed by WipWare, the pioneer in image-based fragmentation analysis and a company dedicated exclusively to this discipline, it remains one of the most reliable and trusted technologies available today. When an organization concentrates its expertise on a specific area, much like a ruler designed for a precise purpose, it naturally excels. WipWare’s long-standing focus on fragmentation analysis exemplifies this principle. How WipFrag Helps: Quantify Fragmentation Differences By analyzing muckpile or truck-loading images before and after stemming adjustments, WipFrag provides: Full particle size distribution, bounder count and trend, %fine for each blast, These metrics show whether fragmentation improved or deteriorated following stemming modifications. WipFrag fits perfectly into a Plan–Do–Check–Act process: Plan: Adjust stemming length based on modelling or previous results Do: Implement the blast design Check: Measure fragmentation with WipFrag Act: Refine stemming parameters based on performance This closes the loop and ensures that stemming design evolves with actual site conditions, geology, and production requirements.

Lessons on the Effect of Fractures on Rock Fragmentation Rock fragmentation during blasting is strongly influenced by the interaction between stress waves and geological structures. Weak or less stiff zones, such as joints, bedding planes, or other discontinuities, reflect the incoming shock wave during detonation. This reflected energy increases damage on the opposite side of the discontinuity, often producing coarser fragmentation in those areas. Conversely, stronger and stiffer rock units transmit stress waves more efficiently. Blasting produces three primary damage zones within the rock mass: Crushed Zone This forms immediately around the borehole where the explosive shock wave exceeds the rock’s dynamic compressive strength, pulverizing the rock. Fracture Zone As the stress wave travels outward, the rock yields when the induced tensile stresses surpass the dynamic tensile strength. This creates radial and circumferential fractures extending several hole diameters from the blast hole (Ding et al., 2022). Spalling Zone The spalling zone develops when stress waves encounter a free face. The wave reflects back as a tensile wave, and if this reflected tensile stress exceeds the rock’s tensile strength, slabbing or thin “tile-like” breakage occurs (Zhang, 2016). The size and intensity of these zones depend on explosive type, energy characteristics, and rock mass properties. Influence of Geological Structures and Impedance The impedance mismatch between intact rock and geological structures also significantly affects the transmission and distribution of stress waves. When stress waves pass through materials with different densities or stiffness, their speed and amplitude change. This alters fragmentation patterns, influences damage zone extent, and affects material throw. Numerical and Field Evidence Numerical and field studies by Magreth Dotto Ph.D., P.Eng. and Yashar Pourrahimian provide valuable insight into damage distribution in jointed rock masses under blast loading: Their LS-DYNA numerical model for 51 mm holes shows the crushed zone radius extends 87.71 mm, approximately 1.72 times the borehole radius. Using peak particle velocity (PPV) criteria, the fracture zone extends to 3.02 m, or 59.2 times the hole radius. Field trials confirmed these results, with a crushing radius of 93.09 mm and a fracture radius of 3.1 m. PPV measurements showed a significant drop from 102 m/s near the hole to 2.35 m/s beyond the fracture zone indicating the rapid attenuation of energy after fracturing. Key Takeaway for Blasting Engineers A critical lesson from these findings is that the fracture zone generated around each blast hole must remain within the hole’s burden and spacing. If the induced fracture radius exceeds or become lesser than these design parameters, fragmentation becomes inconsistent and inefficient. Understanding the fracture zone radius is essential for designing burden, spacing, and energy distribution that deliver optimal fragmentation.

This is a basics calculations for loading the holes in and Blast activity

Blast design: How engineers plan hole patterns, depths, and timing to break hard rock efficiently. Fragmentation: How blasting makes rock easier to excavate and transport. Safety: Controlling fly rock, dust, vibration, and ensuring workers stay safe. Mining operations: How blasting impacts productivity and overall mining efficiency.

Here’s a more detailed description you can use: This review by M. Cardu explores the significant benefits of **electronic detonators** compared to conventional blasting systems in mining. Electronic detonators provide **exceptionally precise timing**, which allows engineers to control the sequence of explosions more accurately. This precision leads to **better rock fragmentation**, **reduced vibration and airblast**, and overall **safer and more efficient blasting operations**. The paper also explains how these systems improve productivity, lower operational costs, and enhance the predictability of blast results. It’s a valuable resource for understanding modern blasting technology and its role in improving mine safety and performance.

• 15g Stinger. White coloured, is used in small diameter holes (45mm or less). • 150g booster. Yellow coloured, is in small holes up to 150mm in diameter. • Y-3 booster. Green coloured and conical. Is used to initiate large diameter holes exceeding 150mm in diameter. Mostly at opencast mining operations. • C 400 booster. Red coloured and conical, to initiate large diameter holes exceeding 150mm in diameter. • C 800 booster. Oranger coloured. Is used in deeper blast holes (25m and more).

[PT]Há quem diga até hoje que a onda de choque produzida pelo demonte de rochas com explosivos não induz danos microestruturais na matriz da rocha, reduzindo portanto, sua resistência mecânica e consequentemente seu pré-requisito energético para cominuição. Provar este fato é mais simples do que parece, e basta medirmos a velocidade de pulso utrassônico das amostras de rochas antes e depois da detonação. Para mais detalhes, confira o post completo aqui na plataforma ZVENIA. [EN] Some people still argue that the shock wave produced by rock blasting with explosives does not induce microstructural damage to the rock matrix, thus reducing its mechanical strength and, consequently, the energy required for comminution. Proving this fact is simpler than it seems; all we need to do is measure the ultrasonic pulse velocity of rock samples before and after detonation. For more details, check out the full post here on the ZVENIA platform. https://zvenia.com/z-posts/estado-de-fraturamento-e-fragmentacao-de-macicos-rochosos-tese-de-doutorado-2020/

Final Wall Control: Understanding and Applying the Half-Cast Factor in Open Pit Mining In open pit mining, achieving a stable and geotechnically compliant final wall depends heavily on how effectively blasting energy is controlled along the designed slope. One of the key quality control measures in this process is the Half-Cast Factor (HCF), a simple yet powerful indicator of how well the pre-split or final wall blast performed. The methodology to calculate the Half-Cast Factor involves measuring the number of visible half-casts (pre-split barrels) along a given section of the final wall and dividing it by the total number of pre-split holes drilled in that section. For instance, if 20 holes were drilled and 15 half-casts are visible, the resulting HCF is 0.75 (or 75%). Mathematically: "Half-Cast Factor"="Length of visible half-casts" /"Total length of pre-split holes" X 100% A high Half-Cast Factor (≥ 0.8) indicates that the blast energy was well confined between the pre-split holes, maintaining a clean separation between the final wall and the blasted rock mass. Conversely, a low HCF (< 0.6) suggests excessive energy or poor coupling, leading to overbreak, crest damage, and loss of wall integrity (Jeroen van Eldert, 2018) Carrying out this exercise routinely is critical because it allows mining and geotechnical teams to: ✅ Assess final wall stability by quantifying blast-induced damage. ✅ Calibrate blast designs, adjusting burden, spacing, and charge per hole for improved wall control. ✅ Reduce future remediation costs associated with scaling, rock bolting, or catchment redesign. ✅ Support slope monitoring programs by correlating Half-Cast Factor results with radar or prism movement trends. The photo below shows a well-defined pre-split wall, with visible half-casts demonstrating good control along the final face, a sign of precise drilling, accurate timing, and optimal charge confinement. Ultimately, monitoring the Half-Cast Factor transforms wall control from a visual inspection to a quantitative performance metric, ensuring safer, steeper, and more economical slopes, the true foundation of sustainable open pit operations

Understanding Powder Factor in Open-Pit Blasting Engineering By Mohamed Salah Alansary Senior Drill & Blast Engineer – Zvenia Mining | Egypt Country Manager ________________________________________________________________________________________________________________ Introduction Powder Factor (PF) is one of the fundamental parameters in drill and blast engineering. It defines the ratio between the mass of explosives used and the volume or mass of rock blasted. Despite being a simple ratio, Powder Factor governs the overall performance of blasting operations and directly impacts productivity, cost efficiency, and downstream processes across the mine site. ________________________________________________________________________________________________________________ Definition Powder Factor is expressed as: PF = Explosive (kg) / Rock (m³) or PF = Explosive (kg) / Rock (tonne) This ratio indicates the quantity of explosive energy applied per unit of rock. The primary objective is to match the explosive energy to the rock’s resistance, ensuring effective fragmentation without excessive energy consumption. ________________________________________________________________________________________________________________ Purpose The purpose of optimizing Powder Factor is to achieve efficient energy utilization during rock breakage. The correct PF results in uniform fragmentation, optimized shovel loading, efficient crusher performance, and reduced operational costs. Conversely, incorrect Powder Factor values may cause poor fragmentation, high boulder generation, excessive vibration, or unnecessary explosive consumption. ________________________________________________________________________________________________________________ Operational Impact Powder Factor influences several key operational aspects: Fragmentation: Determines particle size distribution, influencing loading, hauling, and crushing efficiency. Drill and Blast Cost: Controls the balance between explosive consumption and fragmentation quality. Productivity: Affects the loading rate, cycle time, and overall mine output. Environmental Control: Impacts vibration levels, flyrock, and airblast management. A well-optimized PF provides a balance between fragmentation quality, cost, and environmental control. ________________________________________________________________________________________________________________ Typical Ranges Powder Factor varies based on rock hardness and geological conditions. The following ranges are generally accepted as guidelines: Rock Type Typical PF (kg/m³) Soft Rock 0.3 – 0.6 Medium-Hard Rock 0.6 – 0.9 Hard Rock 0.9 – 1.2 These values serve as reference points. Actual PF selection should be determined through on site trials, monitoring, and data driven analysis. ________________________________________________________________________________________________________________ Advanced Considerations At an advanced level, Powder Factor is linked to blast energy distribution, burden and spacing design, and overall blast efficiency. Modern software tools allow engineers to simulate PF adjustments and predict outcomes before field implementation. Engineers should consider the Powder Factor as part of an integrated system that includes hole diameter, bench height, subdrill, stemming length, and explosive type. Proper evaluation ensures consistency between design intent and actual blast results. ________________________________________________________________________________________________________________ Practical Insights In general: -Higher PF tends to produce finer fragmentation but increases explosive costs. -Lower PF typically results in coarser fragmentation, reduced energy efficiency, and may increase secondary breakage requirements. The optimal value lies between these extremes, depending on operational goals, rock type, and downstream constraints. ________________________________________________________________________________________________________________ Conclusion Powder Factor remains a key indicator of blast performance and a vital control parameter in open-pit mining. It is not a fixed value but a dynamic variable that must be adjusted based on actual ground conditions, geology, and operational targets. Ultimately, achieving an effective Powder Factor requires technical understanding, continuous monitoring, and practical experience.

[PT] O estudo compara vários geradores de dados e testa conjuntos reais, sintéticos e mistos para prever PPV. O melhor resultado aparece com dados híbridos (real + sintético), que reduzem erro e aumentam o R². Para o dia a dia, isso significa modelos mais estáveis com o mesmo volume de dados coletados. É ganho direto em qualidade de previsão. [EN] This study compares several generators and tests real, synthetic, and hybrid datasets for PPV. Hybrid data (real + synthetic) yield lower error and higher R². Day-to-day, that means more stable models without collecting tons of new data. A clear win for prediction quality.

[PT] Várias combinações de ML são testados para prever PPV com mais precisão e robustez. O estudo também usa stacking e aumento de dados para melhorar o resultado e SHAP para explicar quais variáveis mais pesam. É um guia prático para escolher modelos que funcionem bem mesmo com poucos dados. Ótimo para equipes de desmonte que querem mais acerto e mais transparência. [EN] This project tests multiple ML ensembles to predict PPV with better accuracy and robustness. It adds stacking, data augmentation, and uses SHAP to explain which features matter most. It’s a practical guide when you have limited data. Great for blasting teams seeking higher accuracy and clearer explanations.

[PT] O estudo cria um modelo para prever PPV (vibração de desmonte) e compara fórmulas empíricas com ML. O melhor desempenho vem de um modelo híbrido que escolhe bem as variáveis e ajusta os parâmetros automaticamente. Na prática, ajuda a definir carga máxima por retardo e reduzir incômodo em áreas vizinhas. É um passo simples para controlar vibrações com dados reais. [EN] This work builds a PPV predictor and compares empirical laws with ML. A hybrid model that selects features and tunes hyperparameters performs best. In practice, it helps set maximum charge per delay and cut annoyance in nearby areas. A simple, data-driven way to control blasting vibrations.

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