Blast Subdrilling
Calculate the subdrilling of a blast hole, S_p = 0.3 × B, multiplying the burden B by a typical factor of 0.3. The result, in the unit of B, is the length the hole must drill below the desired bench floor level. This extra depth ensures the blast fragments the rock down to the floor level, avoiding toes (ledges of unfragmented rock at the bench foot) that hinder equipment operation. Insufficient subdrilling leaves toes; excessive wastes drilling and explosive and damages the rock below the floor. Enter the burden.
Resultado
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Subperfuração de desmonte
Um detalhe sutil mas crucial do projeto de desmonte: os furos não param exatamente na cota do piso desejado da bancada — eles avançam um pouco abaixo dela. Esse comprimento extra é a subperfuração (subdrilling), estimada por S_p = 0,3 × B (cerca de 30% do afastamento). Por que perfurar abaixo do piso? Porque a região no pé do furo (a base) é a mais difícil de fragmentar — ali a rocha está mais confinada (sem face livre embaixo) e a energia da explosão é menos eficaz. Sem a subperfuração, essa zona não quebra adequadamente, deixando repés (toes, em inglês): saliências ou cristas de rocha não fragmentada ao longo do pé da bancada, no nível do piso. Os repés são um problema operacional sério: criam um piso irregular e elevado que danifica os pneus dos caminhões e o trem-de-força das carregadeiras, reduzem a eficiência do carregamento, comprometem a drenagem da praça, e exigem trabalho extra (desmonte secundário ou raspagem) para corrigir. A subperfuração coloca a carga explosiva abaixo do nível do piso, de modo que a fragmentação alcance e nivele o piso. Mas há um limite: subperfuração excessiva desperdiça perfuração e explosivo, gera vibração desnecessária, e — importante — danifica e fratura a rocha do próximo nível (a futura bancada abaixo), o que pode causar problemas de estabilidade e diluição. Por isso o valor de ~0,3·B é um equilíbrio. Em desmontes especiais (como pré-fissuramento de taludes finais), elimina-se ou reduz-se a subperfuração para não danificar a rocha remanescente. Informe o afastamento.
Related Tools
Detonation Velocity (VOD)
Calculate the velocity of detonation (VOD) of an explosive, VOD = L ÷ t, dividing the distance traveled by the detonation wave L (m) by the time t (s) measured between two sensors. The result, in m/s, is the speed at which the detonation reaction propagates through the explosive column — one of the most important properties of an explosive, linked to its energy and fragmentation power. High-VOD explosives (4000-7000 m/s, like emulsions and dynamites) generate high detonation pressure and are effective in hard rock; low VOD (ANFO, ~3000-4500 m/s) suits softer rock. Enter the measured distance and time.
Blast Hole Count
Calculate the number of holes of a blast pattern, N = area ÷ (burden × spacing), dividing the bench area to blast by the pattern area of each hole (burden B × spacing S). The result is the number of holes needed to cover the area with the specified drilling pattern. In practice, round up. It is an essential quantity calculation in blast planning: it sets the drilling time, the amount of explosive and accessories, and the operation cost. Wider patterns (larger B and S) reduce the number of holes but may worsen fragmentation. Enter the area, the burden and the spacing.
Linear Explosive Charge
Calculate the linear loading density of a blast hole, q = (π/4) × d² × ρ, from the hole diameter d (mm) and the explosive density ρ (g/cm³). The result, in kg of explosive per meter of hole, is how much explosive fits in each meter of charged column — a central parameter of rock blast design. Multiplied by the hole charge height, it gives the charge per hole; combined with the blasted rock volume, it gives the powder factor. Larger diameters and denser explosives raise the linear charge. Enter the hole diameter and the explosive density.
Blast Burden
Calculate the burden of a blast pattern, B = k × d, multiplying a factor k (typically 25 to 40, depending on rock and explosive) by the hole diameter d. The result, in the unit of d, is the distance from the row of holes to the free rock face — one of the most critical geometric parameters of blasting. Too large a burden leaves the rock poorly fragmented (boulders) and creates toes; too small wastes explosive and causes flyrock and overpressure. Together with the hole spacing, the burden defines the drilling pattern and the resulting fragmentation. Enter the factor k and the hole diameter.
Mean Fragment Size (Kuz-Ram)
Estimates the mean fragment size X₅₀ of a blast with the Kuz-Ram model, from the rock factor, the volume broken per hole, the explosive mass per hole and the relative weight strength of the explosive. It is the screen size half the muckpile passes, the number that decides whether crushing will struggle. Enter the four blast design parameters.
Powder Factor
Compute the powder factor of a rock blast by dividing the explosive mass (kg) by the volume of rock broken (m³), in kg/m³. It is the central parameter of the blast design: too low produces boulders and poor fragmentation; too high wastes explosive and increases vibration and flyrock. Optimizing it reduces downstream crushing costs. Enter the explosive mass and the rock volume.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.