Blast Rounds Research Articles

Explosive utilization efficiency enhancement: An application of machine learning for powder factor prediction using critical rock characteristics

Maximizing the use of explosives is crucial for optimizing blasting operations, significantly influencing productivity and cost-effectiveness in mining activities. This work explores the incorporation of machine learning methods to predict powder factor, a crucial measure for assessing the effectiveness of explosive deployment, using important rock characteristics. The goal is to enhance the accuracy of powder factor prediction by employing machine learning methods, namely decision tree models and artificial neural networks. The analysis finds key rock factors that have a substantial impact on the powder factor, hence enabling more accurate planning and execution of blasting operations. The analysis uses data from 180 blast rounds carried out at a dolomite mine in south-south Nigeria. It incorporates measures such as root mean square error (RSME), mean absolute error (MAE), R-squared (R2), and variance accounted for (VAF) to determine the best models for predicting powder factor. The results indicate that the decision tree model (MD4) outperforms alternative approaches, such as artificial neural networks and Gaussian Process Regression (GPR). In addition, the research presents an efficient artificial neural network equation (MD2) for estimating the values of optimum powder factor, demonstrating outstanding blasting fragmentation. In conclusion, this research provides significant information for improving the accuracy of powder factor prediction, which is especially advantageous for small-scale blasting operations.

Validity of the NTNU Prediction Model for D&B Tunnelling

AbstractThe Norwegian University of Science and Technology (NTNU) has since the early 1970s published prediction models for estimated production rates, time consumption, and costs for rock works. Since the early development of the NTNU models the tunnelling industry has continuously improved and the models have been updated on several occasions. The NTNU models are presently being updated to better fit the modern tunnelling trends in Norway. The current prediction model for D&B blast design is in this research paper compared with new data from thirteen recent Norwegian tunnel projects. The paper demonstrates that the empirical methodology behind the prediction model is still highly relevant, but some further improvements and additional empirical relations are suggested to enable the model to better cope with the recent 16 years of development in technology, equipment, contractual-issues and blast design. The new datasets show that modern D&B tunnelling employ more drill holes and specific charging per blast round than before. The current NTNU model thus under-predicts the actual tunnelling performance in the blast design. Some suggestions are made for further improving the model, where the updated drill length, the contour requirements, and the tendency to including the longitudinal ditches into the main blast are suggested as the main reasons for the disparity in drill hole numbers. Yet, the current trend in specific charging seem to have doubled since the early 2000s and cannot be explained by the increase in drill holes alone. Further development ought to be included in the blastability index (SPR) so that geological conditions that are on the extreme side of poor blastability can be properly accounted for in the blast design.

A newly developed blasting cut in tunnels; application of “combined method” in small to medium-sized tunnels

Drilling and blasting method have been widely used for driving tunnels in hard rock. When designing a blast operation especially in case of long tunnels, the primary objective of contractors is to ensure optimized blast parameters for achieving the most economical and time-saving technique of excavation. Choosing a proper blasting cut has a crucial role in the successfulness of the whole blast round in terms of quality, time and cost. The first aim of cut is to break and throw rocks and create a cavity for the upcoming production detonators. An attempt has been made here to test and develop an innovative cutting system for small to medium-scale tunnels where classical wedge cut is physically difficult to execute; what is called in this paper “combined or quasi-wedge method”. Proposed drilling and blasting patterns have been first put in computerized drilling machines and then tested in the tunnels located in Rishikesh-Karnaprayag Railway Project, Package 2, driven in sedimentary rock mass. After thorough investigation of trial-and-error blasts economically and technically, necessary changes have been made to guarantee optimization and find proper design configurations. In comparison to conventional parallel cut, the newly developed cut leads not only to the betterment of cycle time for excavation but also improvement of specific drilling and specific charge, the two main performance indicators of blast operations. Vibration, fragmentation, pull length, fly rock and profile quality, as pro-blast parameters, were also found highly satisfactory.

Assessment of Charge Initiation Techniques Effect on Blast Fragmentation and Environmental Safety: An Application of WipFrag Software

Blast charge initiation procedures have a significant impact on both mining safety and production rates. In this study, the inventory benefit of an electric initiation system was investigated to assess its influence on both fragmentation and blast-induced damages. The WipFrag software was used to examine the size distribution and productivity of 12 small-scale blasts initiated by both nonelectric and electric detonators. All blast rounds were initiated with plain-type electric and NONEL detonators. The average burden, spacing, stemming length, and charge weight were, respectively, 0.85 m, 1.10 m, 0.66 m, and 1.1 kg. The results showed that the mesh through which 80% of the blast fragments passed for the electric blast was smaller than the mesh through which the material products from the NONEL blast passed. The results also demonstrated that the generated blast-induced ground vibration (PPV) from all blast rounds for electric blast varied from 0.4–1.2 mm/s and 80–105 dB, while that for nonelectric blast ranged from 0.05–0.2 mm/s and 72–95 dB. As a result, the electric blast initiation technique was found to produce good fragmentation, with a higher percentage of optimum fragment sizes on spec than nonelectrically initiated blasts.

Rock factor prediction in the Kuz–Ram model and burden estimation by mean fragment size

In order to use the Kuz–Ram fragmentation model efficiently, the rock factor must be determined correctly. One of the aims of this study is to provide an approach to estimate the rock factor, which represents the blastability of the rock mass, in the Kuz–Ram fragmentation model. This proposed approach is based on previous blasting data from quarry records such as blast geometry, explosive quantities and amount of coarse fragmented material to be obtained after blasting. Using the proposed approach, if the mass of the material over a given fragment size is known, the rock factor in the Kuz–Ram model can be determined for a particular site. Another purpose of this study is to estimate the optimal burden according to the intended mean fragment size using the Kuz–Ram model. Studies were firstly carried out to find the most appropriate burden for the mean fragment size intended for a quarry where the rock factor is known. After this, generalized equations were derived for the optimal burden depending on the rock factor, the intended mean fragment size, the bench height and the density of the explosive. Finally, the obtained values from the suggested relations were compared with the actual blast rounds, considering the total cost and the coarse fragmented material ratio. It can be seen that the values obtained from the proposed relationships for burden are compatible with the most cost-effective blast pattern’s parameters that were actually obtained.

Ultrasonic rock microcracking characterization and classification using Hilbert–Huang transform

This study aims to set up a non-destructive method to control the quality of aggregates using ultrasonic wave acquisition and processing. Two applications are presented proving the applicability of the proposed methodology. The first is the characterization and classification of four limestone rocks from cement quarries in the northern part of Tunisia selected from different geological ages (Lower Jurassic, Upper Cretaceous, and Lower Eocene). The second application deals with assessing rock crushing-induced microcracking evolution in quarried rock from the first initial source rock mass to the final aggregate. Five stages were considered: before the blast (bench front), after the blast round (muck pile), after the primary crusher, after the secondary crusher, and after the tertiary crusher. A physico-chemical and ultrasonic characterization was performed on aggregates and core samples in order to identify their characteristics namely the crack porosity and P-wave velocity. A cluster statistical analysis was then adopted to classify the investigated samples into several groups where crack porosity is the most relevant factor in classifying their quality. In addition to measuring ultrasonic parameters such as the spatial attenuation and P-wave velocity, the ultrasonic study looks at the spectrum of the received signal (non-stationary and nonlinear signal) by measuring the instantaneous energy density with the Hilbert–Huang transform. Beyond the fact that the high negative correlation between the P-wave velocity and the instantaneous energy was identified, the methodology developed allowed to prove that the latter is a relevant factor for the classification of limestone rocks.

Combined finite-discrete element modelling of rock fracture and fragmentation induced by contour blasting during tunnelling with high horizontal in-situ stress

A combined finite-discrete element method (FDEM) parallelized on the basis of GPGPU is implemented to model the rock fracture and fragmentation process and the resultant excavation damaged zone (EDZ) development induced by the controlled contour blasting, which was conducted in the TASQ tunnel with high in-situ stresses in the Äspö Hard Rock Laboratory in Sweden. The combination of in-situ stress field, equation-of-state based blast loading, fracturing in tension and shear with gas flow loading of fractures enables the modelling of complex dynamic interactions from multiple blast rounds. For the contour blasting under high horizontal in-situ stresses, blasting-induced fractures initially propagate horizontally, even though the holes are decoupled. Later, these fractures coalesce into larger cracks, which prevents the formation of smooth tunnel walls and increases the EDZ. Smoother surfaces are created at the crown and invert by the propagation of long fractures in the horizontal direction. Due to the combined effect of the free surfaces provided by the adjacent blast-holes and the maximum principal stress induced by in-situ stresses, the fractures at the lower part of the tunnel sidewalls have the tendency to propagate upwards with a diagonal direction about 60° relative to vertical, in accordance with the field test results. Removing the in-situ stresses results in smoother sidewall fracturing with more damage in the crown and invert. Increase in rock heterogeneity, above a threshold, induces more fractures. Increasing the detonation timing between blast-holes induces more damage into the rock mass and fragmentation in the burden. Outcomes of this study show that the GPGPU-parallelized Y-HFDEM IDE provides a powerful tool to replicate the mechanisms of rock fracture and fragmentation induced by blasting.

A comparative investigation of inter-row delay timing vis-à-vis some rock properties on high sandstone benches

The inter-row delay timing plays a pivotal role in any blast round as it not only influences the mechanism offragmentation, but also offers a vast potential in improving the overall results of fragmentation. It is in this perspective thatthe current study presents a comparative investigation of the influence of inter-row delay timing on fragmentation in twodifferent strength sandstone formation in large-scale, multi-row blast rounds of a two surface coal mines in India. Theinvestigations are based on full-scale field blasts. The study highlights the role of p-wave velocity and brittleness vis-à-visimpedance to shock wave propagation during the initial as well as final stages of rock breakage. Given this, the role ofshattering effect (in stronger sandstone formations) and heaving effect in weaker strength sandstone has been clearlyestablished in the rock breakage mechanism. Furthermore, the study also suggests that for weaker sandstone, longer interrowdelay timing (15-25 ms/m of effective burden) yields the best fragment size results. Similarly, for stronger sandstoneformation, shorter inter-row delay timing (10-17.85 ms/m of effective burden) yields the best fragment size results.

A new hybrid ANFIS–PSO model for prediction of peak particle velocity due to bench blasting

In this paper, a novel hybrid approach is proposed for predicting peak particle velocity (PPV) due to bench blasting in open pit mines. The proposed approach is based on the combination of adaptive neuro-fuzzy inference system (ANFIS) and particle swarm optimization (PSO). In this approach, the PSO is used to improve the performance of ANFIS. Furthermore, a model is developed based on support vector regression (SVR) approach. The models are trained and tested based on actual data compiled from 120 blast rounds in Sarcheshmeh copper mine. To determine the accuracy and efficiency of ANFIS---PSO and SVR models, a statistical model (USBM equation) is applied. According to the obtained results, both techniques can be used to predict the PPV, but the comparison of models shows that the ANFIS---PSO model provides better results. Root mean square error (RMSE), variance account for (VAF), and coefficient of determination (R2) indices were obtained as 1.83, 93.37 and 0.957 for ANFIS---PSO model, respectively.

Main challenges for deep subsea tunnels based on norwegian experience

For hard rock subsea tunnels the most challenging rock mass conditions are in most cases represented by major faults/weakness zones. Poor stability weakness zones with large water inflow can be particularly problematic. At the pre-construction investigation stage, geological and engineering geological mapping, refraction seismic investigation and core drilling are the most important methods for identifying potentially adverse rock mass conditions. During excavation, continuous engineering geological mapping and probe drilling ahead of the face are carried out, and for the most recent Norwegian subsea tunnel projects, MWD (Measurement While Drilling) has also been used. During excavation, grouting ahead of the tunnel face is carried out whenever required according to the results from probe drilling. Sealing of water inflow by pre-grouting is particularly important before tunnelling into a section of poor rock mass quality. When excavating through weakness zones, a special methodology is normally applied, including spiling bolts, short blast round lengths and installation of reinforced sprayed concrete arches close to the face. The basic aspects of investigation, support and tunnelling for major weakness zones are discussed in this paper and illustrated by cases representing two very challenging projects which were recently completed (Atlantic Ocean tunnel and T-connection), one which is under construction (Ryfast) and one which is planned to be built in the near future (Rogfast).

Blast vibration effects in an underground mine caused by open-pit mining

The Rampura Agucha open-pit lead zinc mine is producing 5.7Mt/a of ore and has started its underground part, which is slated to produce initially 2–2.4 Mt/a and 4.5Mt/a in the near future. The open-pit mine is currently working at 326m depth and is designed to reach 421m deep. It has been planned to operate the underground mine maintaining 50m parting from the planned ultimate level of the open-pit mine. Presently, open-pit and underground mines are being operated simultaneously. The present average depth of underground working lies between 370 and 410m below the surface level. Sometimes explosives up to 95,978kg are being detonated in a blast round in open-pit mine for speedy removal of overburden. The impact of 86 open-pit blasts has been documented in the underground openings and 258 blast vibration data has been recorded. The vibrations were recorded simultaneously in the roof, sidewalls and at floor levels. The highest levels of vibrations were recorded in the roof and the lowest levels at the corresponding floor levels. The pillars experienced lower level of vibrations than those of the roof. Blast designs were optimised at open-pit mine to control vibration in view of long-term safety and stability of the underground openings. The underground development face blasts were also optimised for the safety and stability of underground workings. Vibrations generated due to detonation of explosives with shock tubes and electronic delay detonators have been recorded in underground openings for comparative assessment. Ground vibration recorded at roof, pillar and floor were analysed separately and threshold value of the vibration for the safety of underground workings has been determined based on the Rock Mass Rating of the roof rock and accordingly blast designs have been optimised.

Comparison of Some Blast Vibration Predictors for Blasting in Underground Drifts and Some Observations

Drilling and blasting are the most economical excavation techniques in underground drifts driven through hard rock formation. Burn cut is the most popular drill pattern, used in this case, to achieve longer advance per blast round. The ground vibration generated due to the propagation of blast waves on the detonation of explosive during blasting is the principal cause for structural and rock damage. Thus, ground vibration is a point of concern for the blasting engineers. The ground vibration from a blast is measured using a seismograph placed at the blast monitoring station. The measured vibrations, in terms of peak particle velocity, are related to the maximum charge detonated at one instant and the distance of seismograph from the blast point. The ground vibrations from a number of blast rounds of varying charge/delay and distances are monitored. A number of scaling factors of these dependencies (viz. Distance and maximum charge/delay) have been proposed by different researchers, namely, square root, cube root, CMRI, Langefors and Kihlstrom, Ghosh–Daemon, Indian standard etc. Scaling factors of desired type are computed for all the measured blast rounds. Regression analysis is carried out between the scaling factors and peak particle velocities to establish the coefficients of the vibration predictor equation. Then, the developed predictor equation is used for designing the blast henceforth. Director General of Mine Safety, India, specified that ground vibrations from eight to ten blast rounds of varying charge/delay and distances should be monitored to develop a predictor equation; however, there is no guideline about the type of scaling factor to be used. Further to this, from the statistical point of view, a regression analysis on a small sample population cannot be accepted without the testing of hypothesis. To show the importance of the above, in this paper, seven scaling factors are considered for blast data set of a hard-rock underground drift using burn-cut blast design. The possible step by step approach to establish a vibration predictor equation is also proposed.

Investigation of Crushed Aggregate as Stemming Material in Bench Blasting: A Case Study

The present paper summarizes the application of two different types of stemming material used in bench blasting. The two stemming material types, namely crushed aggregate and drill cuttings were opted in the present study. The blast trials were conducted on overburden rocks of Garnet Biotite Sillimanite Gneiss (GBSG) formations in one of the largest metalliferous mines of India. These rocks were exposed to polyphase deformations, high-grade metamorphism that comprised of various fissures, joints and foliation planes. An attempt was made through this paper to assess the influence of aggregate stemming material on blasting results. The study revealed that the quality of stemming material significantly influences the blasting performance in moderately strong (UCS 45 MPa) blasting benches of GBSG formations. Hence, the quality of stemming material must be considered in designing blast rounds in such overburden rock formations to achieve production targets. The results were assessed by fragment size measurement in the blasted muck-piles using image analysis technique, excavator performance anticipated by digging rate and muck-pile shape parameters. The fragment size and its distribution affected the digging rate of excavators. The use of crushed aggregate stemming material yielded better fragmentation results in comparison to the drill cuttings in such overburden rock formations. The average fragment size (K50) values for blasts stemmed with drill cuttings were (0.58–0.77 m) higher than that of blasts stemmed with crushed aggregate stemming material (0.45–0.59 m). The digging rate of shovels (34 m3) per hour was consistent and about 18 % higher in blasts stemmed with crushed aggregate stemming material. Muck-pile resulting from every blast was surveyed and throw distance was measured. The average muck-pile throw were 21.2 % higher in blasts stemmed with drill cutting stemming material. Whereas vertical cratering was higher in blasts stemmed with crushed aggregate stemming material.

Assessment of Blasting Performance Using Electronic Vis-à-Vis Shock Tube Detonators in Strong Garnet Biotite Sillimanite Gneiss Formations

This paper presents a comparative investigation of the shock tube and electronic detonating systems practised in bench blasting. The blast trials were conducted on overburden rocks of Garnet Biotite Sillimanite Gneiss formations in one of the largest metalliferous mine of India. The study revealed that the choice of detonating system was crucial in deciding the fragment size and its distribution within the blasted muck-piles. The fragment size and its distribution affected the digging rate of excavators. Also, the shape of the blasted muck-pile was found to be related to the degree of fragmentation. From the present work, it may be inferred that in electronic detonation system, timely release of explosive energy resulted in better overall blasting performance. Hence, the precision in delay time must be considered in designing blast rounds in such overburden rock formations. State-of-art image analysis, GPS based muck-pile profile plotting techniques were rigorously used in the investigation. The study revealed that a mean fragment size (K50) value for shock tube detonated blasts (0.55–0.59 m) was higher than that of electronically detonated blasts (0.43–0.45 m). The digging rate of designated shovels (34 m3) with electronically detonated blasts was consistently more than 5000 t/h, which was almost 13 % higher in comparison to shock tube detonated blasts. Furthermore, favourable muck-pile shapes were witnessed in electronically detonated blasts from the observations made on the dozer performance.

Controlled blasting for long term stability of pit-walls

Controlled blasting techniques were used to control over-breaks and to aid in the stability of the remaining rock mass at Rampura Agucha open-pit mine in India. The mine is a lead zinc mine producing 5.95mtpa of ore and has recently started its underground part, which is slated to produce 4.5mtpa of ore in near future. The mine is currently working at 260m depth, and is designed to reach a depth of 372m. During blasting, back break was the main concern as despite of carrying out pre-splitting; the benches experienced back breaks adversely affecting the stability of the remaining walls. Normal production blast consists of detonation of 6–8 rows involving 140–200 holes in a blast round. A master plan of the pre-split holes position at spacing of 1.2m was prepared. The available explosive was in the cartridge diameter of 25mm which provided decoupling ratio of 1:3.6. Each bench of footwall and of all stages of hang wall is pre-splitted to minimize damage to the rock mass. Pre-split holes of about 700,000m are being drilled annually to get desired pit slopes. In the experimental trials the mouths of the pre-split holes were left without explosives from 0.8 to 2.7m. In the latter stage the inclined holes of 115mm at 80°, 70° and 60° were experimented. The pre-split holes drilled at 1.2m spacing with 60° inclination on footwall and 70° on hangwall yielded desired results.

Assessment of firing patterns on moderately strong and weak sandstone cover rocks in a surface mine

The present paper highlights the application of three different types of firing pattern on two different types of sandstone overburden benches of a large coal mine in India. The study reveals that firing pattern influences the effective spacing to burden ratio at the time of detonation. By changing the firing pattern, effective burden (Be) changes and the ratio of effective spacing (Se) to effective burden (Be) during the firing is also subject to change in comparison to drilled spacing to burden ratio (S/B). Hence, the Se/Be ratio vis-à-vis firing pattern must be used to design the blast rounds. The results have been derived on the digital image analysis based fragment size characterization, excavator performance and evaluation of powder factor values on blasted muck piles. Skewed V-type firing yielded the best results in comparison to straight V-type and normally practiced diagonal firing pattern on the moderately strong sandstone benches, whereas, the existing diagonal firing pattern appears to be satisfactory on weak (weathered and gritty) sandstone benches.

Mapping shotcrete thickness using LiDAR and photogrammetry data: Correcting for over-calculation due to rockmass convergence

The benchmark method of measuring shotcrete thickness from 3D LiDAR and photogrammetry data involves scanning sequential blast rounds, aligning the data in a 3D environment, and calculating the spatial difference between the two models. The calculated difference between the two 3D surface models is measured as the thickness of the sprayed concrete. This methodology does not account for the convergence of the rockmass that naturally occurs between the scanning protocols, nor is it included in the difference equation, and resultantly the user over-measures the thickness of the sprayed concrete. The over-measurement can be corrected through changing the time of scanning with respect to the excavation sequence or calibrating the solution based on known rockmass convergence rates or numerical modelling. The use of 3D imaging data for the calculation of shotcrete thickness will remain a useful tool for geotechnical engineers, but corrections must made to the state-of-practice methodology in order to achieve accurate results.

Mathematical Model to Locate Interference of Blast Waves from Multi-Hole Blasting Rounds

Maximum charge per delay in a blasting round is universally accepted as the influencing parameter to quantify magni-tude of vibration for any distance of concern. However, for any blasting round experimental data reveals that for same charge per delay magnitude of vibration varies with total charge. Considering linear transmission of blast waves, the paper firstly investigates into the influence of explosive weight, blast design parameters and geology of strata on magnitude and characteristics of vibration parameters and thereafter communicates that possibly interference of blast waves generated from same and different holes of a blasting round result into variation in vibration magnitude. The paper lastly developed a mathematical model to evaluate points of interference of blast waves generated from single- and multi-hole blasting round.

A tensile damage model for rocks: Application to blast induced damage assessment

In this paper, an experimental methodology is presented using digital image techniques to assess the internal microcracks and to quantify the rock damage within rock cores. The second part of the work is devoted to the numerical estimation of the tensile blast induced damage evolution law. The set up methodology is then applied to a set of limestone cores which were sampled before and after a real field blast round. The image analysis algorithm which was developed during the present work is based on a segmentation technique that uses a particular thresholding. Petrographic parameters, such as crack number, orientation, extension, centroid position were computed as a first step aiming at a fine characterization of the cracked medium. The most important estimated parameter is the specific crack area which is defined as the ratio between the crack area and the total image area. This parameter was taken as the rock internal damage. A dynamic tensile damage ordinary partial differential equation is numerically solved and calibrated with the obtained data in order to derive a general blast induced damage evaluation law within the muckpile blocks. The application of the numerical algorithm to cores coming from sampled blocks before and after real field blasts allowed the estimation of damage parameter and dynamic stress evolution histories as well as an estimation of the microfracturing activation and growth energies used during the blast.

Development of a New Blast Vibration Prediction Model Incorporating Burden Variations in Surface Blasting

The globally followed common vibration predictor model includes distance from source to vibration monitoring location and quantity of explosive charge per delay without giving much consideration to blast design parameters. Though there are qualitative assertions on the influence of burden on the vibration intensity by many researchers, no work on quantification of influence of burden has been reported. This paper deals with the development of a predictor model incorporating burden deviations in the existing predictor equation. The influence of burden on the vibration was viewed from the angle of detonation and rock fracturing during blasting. The new predictor equation is based on existing models developed by other researchers on the influence of burden on the blasthole pressure and vibration intensity as well as on some logical assumptions. The influence of burden on vibration was examined in two independent phases of blasting, and the net effect was calculated by adding the influence in both the phases. The study provides a quantitative explanation for the common observations of increased vibration levels produced by the blast rounds with excess burden and/or misfired shots.