Small-scale Blast Research Articles

Development of artificial neural network based mathematical models for predicting small scale quarry powder factor for efficient fragmentation coupled with uniformity index model

Blasting is the primary method for reducing rock size in small-scale mining operations. The primary purpose of blasting is to assist rock mass reduction and transportation from the mine to the processing facility. The explosive charge utilized in this blasting operation has an impact on production output, safety, and profitability. The explosive powder factor is used in mining to calculate the quantity of explosive required per mass of rock fragmented, and this study looks at how different powder factors affect blast fragmentation. A machine learning approach was used in this study to optimize explosive use in small-scale quarries. This study employed data from a small-scale dolomite quarry in Akoko Edo, Nigeria, for artificial neural network (ANN) modeling and uniformity index model creation (10 production blasts and 38 blast record datasets). Powder factors greater than 0.7–0.8 kg/m3 result in a lower uniformity index, according to an analysis of monitored blast results. The results showed that powder factors of 0.7 kg/m3 (between 1.6 and 1.7) had the highest uniformity index. According to the findings, the small-scale optimum blast uniformity index is between 1.33 and 1.68. The proposed ANN model performs well in terms of prediction accuracy, as determined by five error indices with coefficients of correlation (R2) of 0.997 on the training dataset and 0.97 on the testing dataset. Based on the model performance analysis results, the suggested ANN model can be used to improve the small-scale blast powder factor in actual applications.

Shock-induced fracture of dolomite rock in small-scale blast tests

This paper attempts to study dolomite failure using small-scale blast tests. The experimental setup consisted of a cylindrical specimen with a central borehole fitted with a detonation cord inside a copper pipe. The specimen was confined using lead material. During the test, acceleration histories were recorded using sensors placed on the lead confinement. The results showed that heterogeneity and initial cracks significantly influenced the observed failure and cracking patterns. The tests were numerically represented using the previously validated Johnson-Holmquist II (JH-2) constitutive model. The properties of the detonation cord were first determined and verified in a special test with a lead specimen to compare the deformation in the test with that of numerical simulation. Then, the small-scale blast test was simulated, and the failure of the dolomite was compared with the test observations. Comparisons of acceleration histories, scabbing failure, and number of radial cracks and crack density confirmed the overall repeatability of the actual testing data. It is likely that the proposed model can be further used for numerical studies of blasting of dolomite rock.

An empirical approach for predicting burden velocities in rock blasting

An analytical relation between burden velocity and ratio of burden to blasthole diameter is developed in this paper. This relation is found to be consistent with the measured burden velocities of all 37 full-scale blasts found from published articles. These blasts include single-hole blasts, multi-hole blasts, and simultaneously-initiated blasts with various borehole diameters such as 64 mm, 76 mm, 92 mm, 115 mm, 142 mm and 310 mm. All boreholes were fully charged. The agreement between measured and calculated burden velocities demonstrates that this relation can be used to predict the burden velocity of a wide range of full-scale blast with fully-coupled explosive charge and help to determine a correct delay time between adjacent holes or rows in various full-scale blasts involved in tunnelling (or drifting), surface and underground mining production blasts and underground opening slot blasts. In addition, this theoretical relation is found to agree with the measured burden velocities of 9 laboratory small-scale blasts to a certain extent. To predict the burden velocity of a small-scale blast, a further study or modification to the relation is necessary by using more small-scale blasts in the future.

Towards a better understanding of the mechanical behavior of a fixed bed of eucalyptus charcoal in a blast furnace using a specific compression test

The properties of wood charcoal layers have an effect on the performance of small-scale blast furnaces. In order to characterize the mechanical behavior of a fixed bed of eucalyptus charcoal, a specific uniaxial compression test was designed and used with charcoal layers of different characteristics. This layer test has the potential to be standardized, and it made it possible to consider the bulk properties of randomly layout charcoal pieces, which was better adapted than single specimen tests in the fiber direction. A total of eight charcoal layers were prepared with two carbonization temperatures (500 °C and 900 °C), two granularities (10 mm and 20 mm), and two different testing temperatures (20 °C and 300 °C). Characteristic parameters of the compression tests were then determined as the particle size distribution, the mechanical energy, and the mean power. The charcoal produced at 900 °C and with a granularity of 20 mm was more resistant to breakage than the others were, and a high quantity of large particles remained after the tests. Significant correlations existed between the carbonization temperature, granularity, and mechanical power of the compression test. The mechanical power was the main parameter that determined the resistance to breakage of a charcoal bed in compression.

Blast wave interaction with structures: an application of exploding wire experiments

The purpose of this research study is to build upon prior shock dynamics research to create an improved experimental setup that can be used to better understand the interaction of shock waves with structures. Large-scale blast wave experiments pose a risk to the individuals running the experiments, the surroundings, and the institution funding them. In contrast, small-scale blast experiments are able to decrease the danger and amount of funding needed associated with each experiment while producing valuable data. Simulations of blast wave–structure interaction may, on the other hand, result in extensive computational times and results that need verification. The exploding wire setup used in this research study has been optimized to consistently produce results at a run-time of less than 100 s per experiment. The adaptable exploding wire setup has a discharge voltage range of 10–40 kV. The configuration includes three main components: the driver, the experimental apparatus, and an ultrahigh-speed imaging system. The original makeup of the exploding wire apparatus allows for flexible adjustments of specifications such as initial detonation, shock wave origin, and magnitude in two and three dimensions. A recent advancement in algorithm tracking has allowed for automated detection of the individual shock fronts. In this instance, the exploding wire apparatus was adapted to simulate city-scale explosions in two dimensions, and the results were compared with numerical simulations.

Internal Fractures After Blasting Confined Rock and Mortar Cylinders

Blast-induced fines in rock negatively influence multiple aspects of raw-mineral sustainability. The Austrian Science Fund (FWF) sponsored a project to investigate the cause of the fines by studying blast fragmentation through small-scale blast tests and numerical simulations. The paper covers the experimental part of the project focusing on internal blast-induced fracturing and related mechanisms. The blast tests were done by blast-loading confined granite and mortar cylinders. The blast-driven dynamic cracking at the end face of the cylinder opposite to the initiation point was filmed with a high-speed camera. Following analyses covered internal crack patterns, fracture surfaces, and sieving of the blasted cylinders to quantify the amount of fine material created. The internal crack patterns and fracture surfaces were analysed by means of computer tomography (CT) and scanning-electron microscopy (SEM). The CT scans show that the amount of explosive charge affects the changing of the topological features of the crack patterns along the cylinder. They also depict different deformation zones around the blast-hole wall with respect to the blasted material and the amount of charge. Although fracture surfaces of larger fragments do not clearly differ in measured roughness and curvature, the SEM scans of smaller fragments show clear difference in fracture surfaces with respect to the blasted material and the amount of charge. SEM scans of thin sections extracted from the blasted cylinders show different fracture features that could be related to the branching/merging mechanism.

Using Small-scale Blast Tests and Numerical Modelling to Trace the Origin of Fines Generated in Blasting

Waste fines from rock breakage often negatively influence economics and environment. The Austrian Science Fund (FWF) sponsors a project to investigate the cause of the fines by studying blast fragmentation throughout small-scale blast tests and numerical simulations. The tests include blast-loading confined granite and mortar cylinders by detonating cord with 6, 12, and 20 g/m of PETN. The blast-driven dynamic cracking at the end face of the cylinder opposite to the initiation point is filmed with a high-speed camera. The filming is followed up by an analysis of surface and internal crack systems and sieving of the blasted cylinders to quantify the amount of fine material created. The numerical simulations cover the blast fragmentation of a mortar cylinder. These simulations use Finite and Discrete Element Methods (FEM, DEM) with explicit time integration. The model cylinders are loaded by a pressure evolution acting on the borehole wall. Both methods produce realistic crack patterns, consisting of through-going radial cracks with crack intersections around a crushed zone at the borehole. Furthermore, the DEM models have also yielded realistic fragment size distributions (FSD). The paper covers the present progress of the ongoing project and related future work.

Detonation effects of shallow buried explosive in sandy soil on target plate acceleration in a small-scale blast test

Small-scale blast tests were carried out to observe and measure the influence of sandy soil towards explosive blast intensity. The tests were to simulate blast impact imparted by anti-vehicular landmine to a lightweight armoured vehicle (LAV). Time of occurrence of the three phases of detonation phase in soil with respect to upward translation time of the test apparatus were recorded using high-speed video camera. At the same time the target plate acceleration was measured using shock accelerometer. It was observed that target plate deformation took place at early stage of the detonation phase before the apparatus moved vertically upwards. Previous data of acceleration-time history and velocity-time history from air blast detonation were compared. It was observed that effects of soil funnelling on blast wave together with the impact from soil ejecta may have contributed to higher blast intensity that characterized detonation in soil, where detonation in soil demonstrated higher plate velocity compared to what occurred in air blast detonation.

Experimental investigation on explosion flame propagation of H2-O2 in a small scale pipeline

The flame propagation law of H2 and O2 premixed gas explosion was studied in a small-scale pipeline experiment with a full size transparent window set up. The experiment consists of a small-scale blast pipe, gas distribution system, ignition system, pressure data acquisition system, high-speed photography system and so on. By setting different conditions of initial concentration and initial pressure, the flame propagation law was studied. Flame propagation images were obtained through a high-speed photography collection system and analyzed for its propagation law. The explosion flame propagation speed was calculated through image processing by MATLAB. The results show that under the condition of the same initial concentration, the higher the initial pressure, the larger the explosion flame acceleration. The maximum explosion pressure has approximate linear relationship to the initial pressure. Under the same initial pressure; when the equivalent ratio is closer to 1, the flame acceleration rate becomes larger, and the explosion pressure reaches the maximum value.

Blast Furnace Operation with 100% Extruded Briquettes Charge

Industrial stiff vacuum extrusion briquettes (BREX) producing line can efficiently provide for the small-scale blast furnace (BF) operation with 100% briquetted charge. Physical and metallurgical properties of the BREX are being investigated. A new effect of the non-linear strengthening of the BREX bonded with the combined Portland cement and Bentonite binder is described. Application of this combined binder results in the local maximum of the cold compressive strength of the BREX on third day of strengthening. Hot strength mechanism of the BREX is explained and was found to be related with creation of the metallized shell on their surface, sintering of the iron-containing particles and further creation of the metallicc phase surrounded by the silicates and ferrites. The addition of the iron ore fines to the BREX composition can improve their sintering during reduction thus helping to keep the integrity of the agglomerates. Results of the industrial operation of the small-scale BF with BREX are analyzed. The consumption of coke in the BF at 100% of BREX does not exceed 500 kg/t compared with 680 kg/t for the smelting without BREX.

Numerical simulation and experimental validation of the dynamic response of aluminum plates under free air explosions

Protection of buildings against explosions due to terrorism actions or accidents is a growing concern in civil engineering. Full-field measuring techniques as well as finite element simulations are two valuable tools in the hands of engineers to understand the structural mechanisms during blast load events. The research leading to this article is motivated by the fact that only limited knowledge about finite element simulations and experimental validation of structures under free air explosions seems to be available. This article investigates the benefits and accuracy of a finite element simulation of a blast loaded thin aluminum plate by validating the results with small-scale blast loading experiments. Experimental data obtained from 3D high-speed digital image correlation, during the first 7ms with a frame rate of 25,000 frames per second, is compared with results obtained from the finite element analysis. The influence of different parameters (amongst others: the element type, element size and integration method) with respect to the accuracy of the finite element results is investigated. It is shown that for the modeling of the deformation of the investigated thin plate, the use of shell elements is allowed as the transverse shear strains appear to be sufficiently small. Furthermore, it is concluded that the use of an explicit integration scheme instead of an implicit scheme dramatically reduces the computational effort without significant loss of accuracy.