Blast-induced Rock Research Articles

Investigation on rock damage associated with ice-filling borehole blasting

Rock excavation and ore extraction in cold regions (e.g., alpine and high-altitude regions) are often conducted using the drill and blasting method. Ice may be presented in boreholes drilled in cold regions due to the potential freezing of water (e.g., water in rock fractures and pores) flowing into boreholes from the surrounding ground. The performance of rock blasting is inevitably affected by the presence of ice and no study has examined the effect of ice in boreholes on rock blasting performance. The present study investigates rock damage induced by the ice-filling borehole blasting. The damage modes and mechanisms of rock mass under the ice-filling borehole blasting are analyzed. The differences of rock damage induced by the sole ice-filling borehole blasting and the ice-water and ice-air mixed filling borehole blasting are identified. The effects of ice volumes in boreholes on blast-induced rock damage are examined. It is found that blast-induced rock damage is greatly reduced as water in boreholes turns into ice. In addition, the blasting with the ice volume greater than 6.7 % filled at the bottom of borehole can induce less rock damage compared to full-coupled charge blasting. To improve the performance of rock blasting with ice-filling boreholes, the effects of two methods, i.e., changing ignition locations and using different types of explosives on rock damage induced by the ice-filling borehole blasting are investigated. An empirical formula of rock damage volume incorporating ice volume, explosive properties, and rock properties is finally proposed as the reference for the design of ice-filling borehole blasting in cold regions.

Extension of reliability information of Z-numbers and fuzzy cognitive map: Development of causality-weighted rock engineering system to predict and risk assessment of blast-induced rock size distribution

Blasting operations in surface mines have the primary purpose of fragmenting the rock mass into a size that is optimal and economically viable for the mine. This ideal size has an impact on every step of the mining operation, from loading and hauling through crushing and grinding. To put it another way, the economics of the mine or facility as a whole are significantly impacted by having the ideal size distribution. This research offers a causality-based rock engineering system (RES) for risk assessment and prediction of rock fragmentation generated by blasting in surface mines. The fuzzy cognitive map was utilized in the proposed approach in order to weight the RES in accordance with the reliability information provided by the Z-number theory. This model of the RES that is weighted according to causality and based on reliability is abbreviated as causality-weighted rock engineering system based on reliability (CWRESR). The construction of the model makes use of a database that was obtained from the Sarcheshmeh copper mine. The findings indicated that the overall risk level of fragmentation was somewhere between high and very high, with a vulnerability index (VI) of 69.73 cm. As a result, controlled blasting operations are strongly advised as a means of lowering the amount of risk. In addition, the suggested model was able to predict rock fragmentation with a coefficient of determination (R2) of 0.9462 and 9646 for the training and testing phase, respectively, demonstrating that the CWRESR model is superior to other models in its ability to predict rock fragmentation.

Numerical modeling of blast-induced rock fragmentation in deep mining with 3D and 2D FEM method approaches

To optimize the excavation of rock using underground blasting techniques, a reliable and simplified approach for modeling rock fragmentation is desired. This paper presents a multistep experimental-numerical methodology for simplifying the three-dimensional (3D) to two-dimensional (2D) quasi-plane-strain problem and reducing computational costs by more than 100-fold. First, in situ tests were conducted involving single-hole and free-face blasting of a dolomite rock mass in a 1050-m-deep mine. The results were validated by laser scanning. The craters were then compared with four analytical models to calculate the radius of the crushing zone. Next, a full 3D model for single-hole blasting was prepared and validated by simulating the crack length and the radius of the crushing zone. Based on the stable crack propagation zones observed in the 3D model and experiments, a 2D model was prepared. The properties of the high explosive (HE) were slightly reduced to match the shape and number of radial cracks and crushing zone radius between the 3D and 2D models. The final methodology was used to reproduce various cut-hole blasting scenarios and observe the effects of residual cracks in the rock mass on further fragmentation. The presence of preexisting cracks was found to be crucial for fragmentation, particularly when the borehole was situated near a free rock face. Finally, an optimization study was performed to determine the possibility of losing rock continuity at different positions within the well in relation to the free rock face.

Investigation of blast-induced rock fragmentation and fracture characteristics with different decoupled charge structures

Decoupled charge structure is widely employed in profile and production blasting of rock engineering, and its breakage effectiveness is closely linked to the utilization rate of explosion energy. In this investigation, the failure patterns and damage extent of cubic red sandstone specimens induced by blasting with various decoupled charge modes were examined through two groups of laboratory tests, and a three-parameter generalized extreme value (GEV) function was introduced to quantify the rock fragmentation size distribution (FSD) characteristics. Moreover, the Riedel-Hiermaier-Thoma (RHT) model parameters were calibrated based on the blasting test result of the R1 sample. Building upon this validated model, dynamic fracture behavior and pressure attenuation process in a dual-hole blasting finite element model with radial and axial decoupled charge structures were reproduced. Notably, the effects of delay time and initiation mode as well as coupling medium on the effectiveness of rock breakage were discussed. The results demonstrated that the three-parameter GEV function offers a more accurate characterization of the FSD features after rock blasting. Additionally, it is observed that the average fragment size decreases linearly with a reduction in the decoupling ratio, leading to a tendency for finer fragments and more uniform FSDs. Besides, through a comparative analysis of energy distribution characteristics and the volume of destruction in various coupling mediums for rock blasting, it is found that water, as a coupling medium, exhibits the highest energy transfer efficiency, followed by wet sand and dry sand, while air shows the least energy efficiency. Furthermore, the theoretical result of the stress transmission coefficient computed using the equivalent wave impedance method can proficiently reflect the extent of rock fragmentation in decoupled charge blasting.

Experimental and numerical investigation on rock fracturing in tunnel contour blasting under initial stress

In tunnel contour blasting, the rock fracturing is generally subjected to in-situ stress. In this investigation, the rock cracking and damage in tunnel contour blasting (smooth blasting and presplitting) under various initial stresses are experimentally and numerically studied. Eight model tests are conducted on tunnel contour blasting with 400 × 400 × 50 mm granite plates. High-speed digital image correlation is employed to identify blast-induced rock fracturing, and image-processing with ImageJ is used to analyse the detailed fracture pattern and rock fragmentation. The variations in fracture networks, fragment size, fractal dimension of rock cracks and fractal damage to rock are thereby examined with increasing stress magnitude and stress dimension. Subsequently, the stress evolution and rock fracturing in model tests are simulated in LS-DYNA, and the energy dissipation during tunnel perimeter blasting is analysed. The investigation results demonstrate that initial stress results in the reduction of length and number of rock cracks under tunnel contour blasting, leading to smaller fractal dimension of crack pattern, less damage into rock and coarser rock fragmentation. Tunnel perimeter excavation performs well under low biaxial stress but tends to fail as the biaxial stress continually increases. Under uniaxial stress, smooth excavation peripheries can be achieved when the centreline of adjacent perimeter holes is parallel to the stress direction, while perimeter excavation is unsatisfactory when the connection line of adjoining boreholes is perpendicular to the initial stress. Comparing smooth blasting with presplitting, it is found that more explosion energy is consumed in rock fracturing during smooth blasting, especially in the excavation zone, leading to a better control of rock fracture and damage in tunnel contour excavation. Therefore, smooth blasting is preferentially recommended for deep tunnelling. Additionally, small burden is also recommended for deep tunnelling with smooth blasting to avoid potential oversize fragmentation in the excavation zone.

Numerical investigation on optimal blasting parameters of tunnel face in granite rock

Overbreak induced by drill and blast method occurs during rock tunnelling. In this study, the performance of three constitutive models for rock material (Riedel-Hienmaier-Thoma, Homlquist-Johnson-Cook, and plastic kinematic models) in simulation of blast-induced rock cracks was investigated, to improve the accuracy of the numerical simulation. The results indicate that the two conventional blast-induced crack simulation methods in LS-DYNA have certain limitations. In contrast, the Riedel-Hienmaier-Thoma (RHT) model characterise the tensile failure behaviour and dynamic fracturing process in rock blasting. Several numerical simulations were performed to quantify the optimal blasting parameters based on the engineering background. An optimal blasting parameters design was proposed and compared with the original blasting parameters. The outcome of the field test demonstrated the feasibility of the optimal blasting parameters.

Numerical investigation on blast-induced rock fragmentation with different stemming structures

Stemming is one of the main concerns in blast of rock engineering due to its impact on explosion energy consumption and rock excavation performance. In this study, blast-induced rock fragmentation under different stemming conditions is numerically studied using combined numerical modelling and image processing. After careful determination the parameters of constitutive material models, the developed numerical model in LS-DYNA is verified based on the blast testing results including rock fracturing and fragment size distribution (FSD). The calibrated constitutive models are then used to model the pressure variation and rock disintegration produced by blasting with different stemming structures. The size data of simulated rock fragmentation are obtained by image-processing the cut surfaces of the numerical model with the program ImageJ, and the blast-created rock FSD is characterized using a three-parameter generalized extreme value function. The effects of the combination of explosive, air/sand deck and stemming on blast-induced rock fragmentation are quantitatively analysed, considering various stemming modes, stemming lengths and air/sand deck lengths. The results show that the blast-created fragment size decreases with an increase in stemming length, a decreasing in air/sand deck length, replacement of top stemming (stemming at borehole collar with air deck) with bottom stemming (stemming directly contact explosive) and alteration of air deck to sand deck, while the FSD range exhibits the opposite tendency. Bottom stemming is recommended for practical blasting due to its efficiency in rock fragmentation and robustness with respect to stemming length.

Quantitative assessment of the effect of in-situ stresses on blast-induced damage to rock

In-situ stress significantly affects rock blast damage but there is a paucity of quantitative assessments of damage evolution in rocks affected by confining pressure. The present paper analyses the effect of envelope pressure on blast-induced rock damage through theoretical analysis and numerical simulations. Damage clouds obtained from numerical simulations are processed using image processing techniques. The concept of the damage variable (η) is proposed to facilitate the presentation of the image processing results. The damage variable is found to be negatively correlated with the hydrostatic pressure (Px) at the same moment, in equiaxial in-situ stress fields. In contrast, in anisotropic in-situ stress fields, η is not negatively correlated with Px due to the presence of hoop tensile stresses in the rock. The mathematical relationship between η and Px in equiaxial and anisotropic stress fields are established. An anisotropic damage variable (ηk) is introduced to describe the effect of the anisotropy ratio (K) on rock damage, which is found to increase with increasing values of K. The sharp increase in K equal to 4 and 5 is explained in terms of the state of the rock stress distribution under static loading. This study provides insights into the effect of in situ stress on rock blast damage and presents new approaches for analyzing and presenting the data.

A 3D nearfield vibration model for simultaneous blasting of multiple holes in the sedimentary rock formation.

Blasting is the most common excavation techniques for sedimentary rocks especially for sandstone. However, blasting process leads to unwanted breakage in the rock beyond the desired perimeter of excavation and such breakage is called blast-induced rock damage or ‘backbreak’. In surface blasting, ‘backbreak’ impacts on bench stability, excavator operation and drilling in the new face. However, prior estimation of extent of rock breakage zone can provide an idea to formulate the blast design to control the backbreak. In the estimation of blast-induced damage zones, vibration-based prediction techniques are one of the popular choices due to their easy applicability in varying geotechnical conditions. The existing vibration-based models are mostly one dimensional and estimate the damage zone only for the single blasthole. However, practically more than one blast holes are blasted to match the production requirement. Sometimes due to improper delay sequence or by using detonating fuse as surface connection, more than one blastholes are blasted simultaneously. Thus, in this study, a damage estimation model is developed based on vibration theory, which can estimate the damage zone generated due to the blasting of multiple holes simultaneously. This model is a three-dimensional model, which considers the position of the blast holes, charges and point of damage in a 3D space. The model is tested in sandstone rock through four numbers of single row multiple holes blastrounds. It is found that the model is predicting damage zone with an accuracy of ± 12%.

Simulation of blast-induced rock tunnel damage using a 3D numerical model

The field tests conducted by the American Engineering Research Associates (ERA) provided important results about the distribution and extension of the damage zones and the failure area that occurred in unlined tunnels as a result of buried explosions in the rock mass surrounding these tunnels. Despite the importance of these results, they did not include specific values for the failure thickness and the fracture angle in the damaged tunnel sections. In the current study, a 3D numerical model is used to simulate one of ERA’s tests using ABAQUS. In this model, the impact of a buried explosion on a tunnel located at (5m) away from the center of the detonation is studied. The results of this model are in good agreement with the published results of ERA’s tests. In addition, the current numerical results give complete values for the change in the failure thickness and the fracture angle over the entire length of the damaged zones of the tunnel. The results of the current study show that the thickness of the failure remains almost constant beyond damage zone 1, while the angle of the fracture decreases remarkably as the charge-to-tunnel distance increases, which causes a decrease in the failure area.

Blasting-induced rock damage control in a soft broken roadway excavation using an air deck at the blasthole bottom

Blasting-induced rock damage control in a soft broken roadway excavation using an air deck at the blasthole bottom

Using a dividing open-pit blast (DOPB) method to reduce ore loss and dilution caused by blast-induced rock movement

Using a dividing open-pit blast (DOPB) method to reduce ore loss and dilution caused by blast-induced rock movement

An uncertainty hybrid model for risk assessment and prediction of blast-induced rock mass fragmentation

Blasting is an important mining operation that usually produce several damaging consequences. Adverse rock fragmentation due to bench blasting is one of them. Hence, analysis of risk level and accurate estimation of particle size distribution of fragment size are of interest. This research developed a new model to simultaneously predict and risk assessment of rock fragmentation using 64 collected data from blasting operated in the Zarshouran gold mine in Iran. In this regard, a newly rock engineering system (RES) is developed based on the reliability information of Z-number theory and causal-effect relationship of the fuzzy cognitive map (FCM). This approach is named the reliability rock engineering causality system (RRECS). To do this, 15 principal effective parameters on rock fragment size were considered in the RRECS modeling process. The uncertainty of the interaction matrix was reduced using Z-number concept. Besides, the weight of effective parameters updated based on the combination of the nonlinear Hebbian algorithm (NLH) and differential evolution algorithm (DE) in FCM. The RRECS performance was validated by statistical linear and non-linear models. The results show R2, RSME, BIAS, and Accuracy using the proposed RRECS model calculated to be 0.957, 1.956, 0.001, and 96.741 for training and 0.931, 0.996, 0.016, and 99.053 for testing parts, respectively. Therefore, RRECS has performed better than the exponential, power, logarithmic, polynomial, and linear models. Furthermore, the sensitivity analysis results revealed that the hole diameter and powder factor parameters have the highest and lowest sensitivity on fragmentation, respectively.

Numerical study on blast-induced fragmentation in deep rock mass

As drilling and blasting technique is applied in deep mining, its practical performance with respect to rock fragmentation becomes a serious concern because high in-situ stress significantly affects the evolution of blast-induced rock cracking, and troubles such as over/under break and insufficient fragmenting may be arisen in deep rock excavation, leading to secondary problems related to the construction costs, ore crushing costs and mineral loss. In this study, the dependences of the blast-induced rock fragmentation on the changes of stress magnitude and stress dimension as well as the depth are investigated using the combined Finite Element modelling and image-processing. After calibrating the numerical model against the blast-induced rock fracture and fragmentation size distribution (FSD) in laboratory blasting test, a series of four-hole models are developed to simulate blast-induced rock fragmentation under various uniaxial stresses, confining pressures, hydrostatic pressures, and 3D in-situ stresses calculated by depths. The corresponding crack patterns are image-processed to provide quantitative insights into blast fragmentation under various in-situ stresses. Following, based on the findings obtained by integrated numerical modelling and image-processing, the effects of in-situ stress on the average fragment size and fragment aspect ratio, and the implications of current findings for practical blasting in deep rock mass are discussed. The results indicate that the blast-induced fragmentation becomes coarser and rounder, and the FSD range gets broader with the increase of stress magnitude and stress dimension as well as depth.

Numerical Investigation of Blast-Induced Rock Movement Characteristics in Open-Pit Bench Blasting Using Bonded-Particle Method

Numerical Investigation of Blast-Induced Rock Movement Characteristics in Open-Pit Bench Blasting Using Bonded-Particle Method

Monitoring rock movement and—controlling ore loss and dilution associated with blasting at Geita and North Mara Gold mines, Tanzania

ABSTRACT We present findings from a blast movement monitoring research conducted as a part of mine to mill campaign at the Geita Gold Mine—and additional data from blast monitoring practices at North Mara Gold Mine. These include measurement of the blast-induced rock movement and perimeter translation after blast derived from a blast shot at Nyankanga pit (Geita Gold Mine) and three other shots at the Nyabirama pit (North Mara Gold Mine). Using Blast Movement Technology, 34 movement-monitoring balls installed in 13 blast-monitoring boreholes made possible estimation of the average vertical and horizontal ore movements in the studied blast shots. Recorded ore movement estimates average horizontal and vertical movements of 3.69 and 1.56 m, respectively, at the Nyabirama pit and average horizontal and vertical movements of 4.5 and 2.48 m, respectively, at the Nyankanga pit. Based on the estimated material movements, zones of ore losses and dilution are established and new dig lines are proposed from successful ore block translation in all blast shots.

Numerical investigation of effect of eccentric decoupled charge structure on blasting-induced rock damage

Numerical investigation of effect of eccentric decoupled charge structure on blasting-induced rock damage

Coupling of material point and continuum discontinuum element methods for simulating blast-induced fractures in rock

A rock blasting simulation method is proposed that couples the material point method (MPM) and continuum discontinuum element method (CDEM). Blast-induced rock fractures are captured by the CDEM using normal and shear springs, and the explosive detonation is simulated by the MPM with a Jones-Wilkins-Lee equation of state. A particle–surface/edge contact method is introduced into the MPM-CDEM to calculate the interaction between the detonation products and rock medium. Three numerical examples are presented to verify the effectiveness of the proposed method. The fracture degree is represented as the ratio of the number of fractured springs to the total number of springs, and is used to analyze the evolution of shear and tension cracks under blasting. The simulation results show that the proposed numerical method well simulates blast-induced rock fractures and considers both progressive rock fracturing and the real explosive detonation. In particular, the expansion of the detonation gas, crushed zone around the blasthole, radial cracks, and effects of pre-existing stress on the blast-induced fractures are all successfully simulated.

Numerical study of blast-induced rock fractures under different in-situ stress and joint properties conditions

As the excavation depth of underground engineering increases, the influence of in-situ stress on the blasting effect cannot be ignored. Many joints in the natural rock mass, coupled with the initial stress, significantly affect the stress wave propagation process. Therefore, it is necessary to study the blast failure behavior of jointed rock masses under different in-situ stress conditions. In this study, a universal distinct element code-discrete fracture network model was used to examine the failure mode of jointed rock mass induced by blasting under different in-situ stress conditions. The effects of in-situ stress and joint geometric parameters on blast-induced rock fractures were analyzed systematically. The numerical results indicated that in-situ stress conditions would act against the initiation and propagation of blasting-induced cracks. The maximum cracking radius and rock breakage area decreased with increasing in-situ stress. The long joints largely prevented the propagation of cracks induced by blasting. However, as a free surface, the joint plane could increase the fracture network scope between the blasting source and joints in the process of blasting. Although it improved the crushing effect of the rock mass considerably, the effect gradually disappeared as the distance between the blasting source and joints or the in-situ stress was increased.

A deep learning approach for rock fragmentation analysis

In mining operations, blast-induced rock fragmentation affects the productivity and efficiency of downstream operations including digging, hauling, crushing, and grinding. Continuous measurement of rock fragmentation is essential for optimizing blast design. Current methods of rock fragmentation analysis rely on either physical screening of blasted rock material or image analysis of the blasted muckpiles; both are time consuming. This study aims to present and evaluate the measurement of rock fragmentation using deep learning strategies. A deep neural network (DNN) architecture was used to predict characteristic sizes of rock fragments from a 2D image of a muckpile. The data set used for training the DNN model is composed of 61,853 labelled images of blasted rock fragments. An exclusive data set of 1,263 labelled images were used to test the DNN model. The percent error for coarse characteristic size prediction ranges within ± 25% when evaluated using the test set. Model validation on orthomosaics for two muckpiles shows that the deep learning method achieves a good accuracy (lower mean percent error) compared to manual image labelling. Validation on screened piles shows that the DNN model prediction is similar to manual labelling accuracy when compared with sieving analysis. • Deep neural network trained to predict sizes of rock fragments from an image. • Data set composed of 61,853 labelled images of rock pile fragments. • Percent error for coarse size prediction ranges within ± 25% for test set. • 50% of the test set has a prediction percent error of ± 10%. • Validation on sieved piles shows accurate prediction compared to image labelling.