Rock Blasting Research Articles

Contribution of detonation gas to fracturing reach in rock blasting: insights from the combined finite-discrete element method

Contribution of detonation gas to fracturing reach in rock blasting: insights from the combined finite-discrete element method

Blast-Fragmentation Prediction Derived From the Fragment Size-Energy Fan Concept

The size-energy fan concept formulation is developed into a prediction model of the fragment size distribution from blast design and rock mass variables. The fragment size is scaled with a characteristic size of the blast and the rock mass discontinuity spacing and orientation. The energy is scaled with the rock strength and the cooperation degree between adjacent holes. A cooperation function is introduced that modifies the energy with the in-row delay, non-dimensionalized with the P-wave velocity and the holes spacing. The cooperation increases as the delay increases up to a certain value, beyond which the cooperation decreases and the fragmentation is coarser. Several prediction models are presented, using the Swebrec-based fan slopes function of the percent passing as starting point, with subsequent improvements involving alternative formulations of that function, that encompass a non-Swebrec underlying distribution of the fragment size. The models include 12 to 14 parameters, controlling the effect on fragmentation of the variables describing the rock mass, the explosive and initiation sequence, and the blast geometry. The parameters are determined from fits to the data base that was used for the xP-frag model, expanded with seventeen additional blasts. All fragmentation data used are mass size distributions determined by sieving and weighing of blasted muckpiles. The different models are introduced sequentially and discussed. The models presented improve the performance of xP-frag, while including a much smaller number of parameters and, unlike xP-frag, keeping the physically sound size-energy fan pattern, effectively extending its nature from a descriptive frame of the fragmentation-energy relations, to a predictive tool.

Study on the blasting damage of prestressed rock-like specimens with different coupling mediums

The performance of rock blasting is significantly influenced by the coupling medium between the explosive and borehole wall. In this study, two shear-thickening fluids (corn starch suspension (CSS) and silica dioxide suspension (SDS)) and water, were used as coupling mediums. The blasting tests were conducted on cement mortar specimens under coupled blasting load and uniaxial static stresses ranging from 0 to 7.5 MPa at intervals of 2.5 MPa. Fractal theory was employed to analyze the extent of damage, crack extension and fractal characteristics of the 3D reconstructed specimens after blasting. The experimental findings revealed that specimens using SDS showed a decrease in damage followed by an increase with increasing static stress, presenting an opposite trend compared to specimens using CSS. The specimens using water exhibited intermediate results. Furthermore, numerical simulations were performed to understand the stress transmission from explosive transferring coupling medium to rock under blasting loads. The variable viscous characteristics of the coupling medium led to divergence in blast load propagation and decay, directly influencing the damage to the specimen. Under blasting load, CSS with a stronger shear-thickening effect played a beneficial buffering role, reducing the strength of the blasting load and minimizing specimen damage. On the other hand, SDS with a weaker shear-thickening effect demonstrated better stress wave propagation ability compared to water. This was reflected in the higher maximum pressure exerted by SDS, as well as the more uniform distribution of pressure, maximum shear stress, and resultant velocity along the borehole wall. The study also highlighted the potential for adjusting blast stress wave distribution by changing the detonation point's location and emphasized the advantages of CSS and SDS as stemming materials in boreholes.

Study of rock damage characteristics in decoupled slit charge blasting based on computer tomography scanning

Controlling blast load damage and destruction of the remaining rock mass in rock blasting has been the focus of scientific research. By studying various decoupling ratios of the slit charges, blasting experiments and numerical calculations of the small charge were carried out on the glauconite specimen. The internal fracture and damage characteristics of the damaged specimens (post blast) were quantified by computed tomography (CT) scanning and three-dimensional (3D) model reconstruction. The results showed that the damage to the glauconite specimens was mainly radial, with the main crack surface in the slit direction and the “X-type” and “Y-type” non-slit directions. With the increase in the decoupling ratio of the slit charge, the fractal dimension of the explosion crack face tends to increase, and the degree of damage gradually increased; When the decoupling ratio was 1.67, the fractal dimension of the explosive crack surface decreased, the smallest degree of damage. LS-DYNA simulation software was used to study the dynamic fracture process and the effective stress peak of the blasthole wall in the slit and non-slit directions for different decoupling ratios of the slit charge. The numerical calculation results showed that with the increase in the decoupling ratio, the peak effective stress of the blasthole wall characteristic unit in the slit direction was larger than that in the non-slit direction; The effective stress peak showed an increasing trend, and the maximum peak effective stress was 567.7 MPa when the decoupling ratio was 1.67. Therefore, this method can be a suitable means to reconstructing the spatial distribution of internal cracks and numerical calculation to evaluate the damage mechanism of slit charge blasting; Furthermore, within the range of the optimal slit charge decoupling ratio, this method can guide the site to prevent the damage and destruction of the remaining rock mass, allowing for more, allocation and utilization of the explosion energy.

Deep Rock Blasting Using Decoupled Charge with Different Coupling Mediums

Blasts using decoupled charge with various coupling mediums are extensively operated in underground excavation, and blasting challenges are always encountered in deep rock mass due to the influence of high in-situ stress. In the present study, the dynamic responses of deep rock mass in blasting with decoupled charge and different coupling mediums (air, dry sand, wet sand, and water) are theoretically and numerically investigated. First, the transmission, propagation, and superposition of stress induced by blasting coupled with different coupling materials, and the effect of static stress distribution around boreholes on the crack initiation and propagation in blasting under conditions of varying hydrostatic pressure and anisotropic in-situ stress are theoretically analyzed with a two-hole planar analytical model. Then, a numerical model is constructed and verified against the rock fracture network obtained from a blasting test. Based on the verified numerical model, two-hole planar computational models with the same configuration as the analytical model are developed and used to perform a series of simulations. The joint effect of the coupling medium and the in-situ stress on the initiation, propagation, and interconnection of blast-induced cracks are numerically analyzed and interpreted by combining with theoretical results. The analytical and numerical investigations indicate that the evolution of blast-induced cracks in deep rock mass is mainly controlled by the stress transmitting from explosive to rock, superposition of explosion stress waves, as well as the magnitude and orientation of in-situ stress. Finally, the implications of current findings for practical blasting in deep rock mass are discussed. This study develops the understanding of rock cracking induced by blasting with different coupling mediums under high in-situ stress and provides some guidance to solve blasting difficulties in deep rock mass.

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.

Numerical Analysis of Directional Rock Blasting with Continuous-Discontinuous Element Method

When simulating the directional blasting process, many researchers focus on the cutting and splitting effects who might pay more attention on the crushing effects when studying conventional cut blasting. In this case, a numerical tool capable of capturing the strong discontinuity processes of quasi-brittle materials is highly preferable, where many blasting parameters should be calibrated and inputted. In this work, a hybrid finite-discrete elements method with explicit iterative procedure named Continuous-Discontinuous Elements Method (CDEM) is adopted to study the directional rock blasting processes. Landau model is used to capture the detonation effects, where the parameters are calibrated by comparing to the results provided by published literatures. We found that: i) The crack propagation mode of directional rock blasting is similar to those found in Brazilian splitting tests where the crack initiates from the midpoint of the connecting line of blast holes; ii) Compared with traditional cut blasting, the free surface has no significant influence on the blasting effect of directional cut blasting, while the spacing of the hole has great influence on the cutting effect. The index of fracture degree can be used to evaluate the blasting effect quantitatively. This work partly reveals some cracking patterns and rules of directional rock blasting, which may assist the engineers to develop improved precise blasting technologies.

PROTECTING THE ENVIRONMENT AROUND POLISH QUARRIES FROM HARMFUL SEISMIC VIBRATIONS CAUSED BY ROCK BLASTING

The paper presents the legal and scientific conditions for Polish researchers to determine the vibration velocity and the radius of the safe zone of seismic vibrations generated during rock blasting. Until now, in Poland and worldwide, it has been assumed that seismic vibrations generated during rock blasting with explosives [BM] propagate circularly with equal energy in each direction. However, this is not always the case. A theoretical analysis of the variation of the tangential magnitude Vy of the vibration velocity as a function of the change of the direction angle was carried out for a circular distribution of the vibration velocity. It was shown that the value of the vibration velocity component at the same distance from the vibration source depends on the directional angle between the line of the blast holes and the line connecting the centre of the surface of the excavated BM block and the measuring point. New relationships have been given that take into account the directional angle in the calculation of the maximum values of vibration velocity necessary for the determination of the resulting damage in the building from the SWD. A dynamic impact scale [SWD] for the assessment of building damage as the vibration velocity acting on the building increases is given and discussed. Vibration velocity diagrams measured during the excavation of BM rock have been presented for circular distributions in accordance with theoretical predictions. A vibration velocity diagram for an elliptical distribution, inconsistent with a circular distribution, measured during the excavation of BM rock is presented. It is shown that the directionality of the horizontal tangential component of the vibration velocity exists for both circular and elliptical distribution of vibration velocity in rock excavation with explosive BM. The technical safety of the building in the area of seismic vibrations is determined by the vibration velocity included in zone II of the scale of dynamic influences [SWD] Fig.6A ,6B.

Theory and numerical simulation of deep hole cut blasting based on dispersed charge and staged detonation

The rock drilling and blasting method is the most commonly adopted method for rock roadway excavation in China, where cutting efficiency is the key factor affecting the excavation speed. The conventional wedge-shaped cut blasting is not suitable for deep hole blasting since the method requires the explosives to be concentrated at the bottom of the borehole, resulting in uneven fragmentation of the upper rock and difficulty in throwing the bottom rock. In addition, the cut area is small, and the range of cavity created after cut hole blasting cannot meet the needs of large section blasting tunneling. This present study proposes an efficient method for charging and detonation inside and between boreholes called disperse charge and staged detonation (DCSD) cut blasting technique. The DCSD cut blasting and traditional wedge cut blasting models were established and compared using the smooth particle hydrodynamics-finite element method (SPH-FEM). The results shows that the DCSD model reduces the minimum resistance line of rock blasting and creates a new free surface, promoting the throwing of the bottom rock mass and the overall rock mass failure. Furthermore, the cutting efficiency is defined to quantitatively analyze the influence of different parameters on the cutting effect. The cutting efficiency of the DCSD model with dispersed charge is 21.89% higher than that of the blasting model with continuous charge. The cutting effect is at its greatest for the three types of ε designed for the study, when ε = 0.5. The increase in hole depth reduces the cutting efficiency marginally, although it is still higher than that in the traditional mode. Finally, the successful application of digital electronic detonator and DCSD in domestic rock roadway blasting construction verifies the applicability of DCSD and provides a reference for subsequent projects involving rock roadway deep hole drilling and blasting construction.

Effect of Different Filling Media Between Explosive and Blast-Hole Wall on Rock Blasting

Effect of Different Filling Media Between Explosive and Blast-Hole Wall on Rock Blasting

Dynamic tensile strength of rock specimens with different defect lengths

Rock masses contain defects at various scales. The presence of these defects and imperfections must be considered in the design of rock structures particularly when dynamic loading due to earthquake or rock blasting is involved. The role of an existing defect or notch on the tensile strength of a synthetic rock under static and dynamic loads is examined in this study. Brazilian specimens with diameter = 50 mm and thickness = 10 mm were prepared from molded gypsum to represent the synthetic rock. Both intact and notched specimens were tested. The mode I loading was applied to the specimens; the notch was aligned with the applied diametric line load. The Split Hopkinson Pressure Bar (SHPB) equipment was utilized for the dynamic testing. Different notch lengths of 10 to 40 mm were considered. The Bonded Particle Model (BPM) was employed to identify the crack formation and evolution in the specimens for the numerical analysis. The numerical simulation was performed byemploying the CA3 finite element - bonded particle software. The whole SHPB device was modeled, including the incident and transmission bars, together with the rock specimen. The physical and numerical data suggest that specimens with notches demonstrate stronger responses to the stress rate compared to the intact specimens. In particular, the fracture toughness increases substantially as the loading rate is intensified. Furthermore, it is shown that while the physical and numerical static tensile strengths decrease as the notch length increases, the dynamic tensile strength remains unchanged with increasing the notch length when loading rates of high intensity are applied. The reason for this observation is scrutinized and it is shown that the crack tip opening velocity is responsible for this peculiar finding. The numerical model is able to capture this phenomenon due to the appropriate rate dependent micromechanical model used in this study. Finally, based on the published studies and the results of this work, an equation is derived which suggests a linear relationship between the rock tensile strength and the strain rate. This equation is valid for the physical and numerical specimens with different notch lengths.

Characteristics and Energy Distribution of Blast-Induced Ground Vibration in Deep-Hole Blasting

This study proposes an incremental extreme extraction method based on the waveform characteristics of ground vibration signals obtained from open-pit mines to investigate the distribution and characteristics of ground vibration from deep-hole blasting. Firstly, an incremental extreme extraction method is proposed based on the waveform characteristics of borehole blasting vibration signals in open-pit mines. The proposed method could extract and screen the extreme values of blasting vibration signals and effectively improve the utilization rate of the data. The space vector of particle vibration is introduced to analyze the angle change between the particle velocity vector and the ground surface when the extreme value increases. Finally, the relation between the particle velocity vector and the angle between the ground plane and the increasing extremum position of several sets of measured signals is studied. Based on the statistical analysis, the results show that the particle velocity in the vertical direction has a significant advantage over that of the other two directions, and the angle between the extreme particle velocity vector direction and the ground plane is primarily distributed in the range of 60°~90°. After an unstable distribution of particle velocities in the transition zone, the particle velocities in each direction gradually attain a relatively balanced and stable attenuation condition as the distance increases. This proves the reliability of the proposed vector analysis of particle velocity in understanding the mechanism of rock blasting.

Technical safety of buildings around polish quarries against harmful seismic vibrations caused by rock blasting

This paper presents the results of measurements of the elliptical distribution of seismic vibrations generated during rock blasting.The technical safety of a building in the area of seismic vibrations is determined by the vibration velocity that does not exceed the line B included in zone II of the scale of dynamic influences [SWD]. The hypothesis proved in the paper is that for both elliptical and circular distributions of the vibration velocity in rock mining with blasting material [BM] there is a directionality of the horizontal radial component Vx and the tangential component Vy of the vibration velocity.The magnitude of the components Vx and Vy of the vibration velocity at the same distance from the vibration source depends on the directional angle "α" between the line of the blast holes and the line connecting the centre of the surface of the rock block being mined with [BM] and the place of measurement. The elliptical shapes of the graphs Vx and Vy obtained during the mining of the BM of the basalt deposit, which depend on the value of the directional angle, were compared with the shape of the circular velocity graphs Vx and Vy. New correlations are given that take into account the directional angle when calculating the maximum vibration velocity values needed to determine the damage caused to a bulding by the SWD.A dynamic impact scale [SWD] for the assessment of building damage as the vibration velocity acting on the building increases is given and discussed. Vibration velocity diagrams measured during the excavation of BM rock are presented for circular distributions in accordance with theoretical predictions. A vibration velocity diagram for an elliptical distribution, inconsistent with a circular distribution, measured during the excavation of BM rock is presented. It is shown that the directionality of the horizontal radial and tangential components of vibration velocity exists for both circular and elliptical distribution of vibration velocity in rock excavation with BM. In the conclusions, for the elliptical velocity field of the vibrations, the conditions to be observed in order to be able to direct the smallest vibrations towards the built up area are given.

Experiments and simulation of block motion in underwater bench blasting

The blasting mechanism underlying drilling and blasting of underwater rocks, as an important component of the engineering blasting technology, has not been systematically studied. Laboratory model experiments are expensive and take a long time, while field tests fail to obtain timeous breakage and accumulation effects of underwater blasting, and may even be impossible. Considering this, a model experiment of underwater concrete bench blasting was designed, and the motion of blasted blocks was observed and evaluated with a high-speed camera. Then, numerical simulation was conducted based on Fluent and an engineering discrete element method coupling program complied using the application programming interface. Results show that the blocks form a bulge in the underwater blasting experiment under action of blast waves and expansion in the first period of bubble pulsation. Then, some blocks shrink in the first period of bubble pulsation. As the charge increases, the blast load exerts larger disturbance on the block group, resulting in significant motion of blasted blocks along the vertical direction. At the same time, the horizontal displacement of blasted blocks in the throwing direction increases.

Investigation of the Microseismic Response Characteristics of a Bottom Structure’s Ground Pressure Activity under the Influence of Faults

To further understand the changing pattern of the bottom structure’s ground pressure activity under the influence of faults, predicting the potential occurrence of geological hazards and rock blast problems to reduce the loss of resources is important. A new microseismic monitoring system was established based on the original Pulang copper mine microseismic monitoring system. This paper analyzed the change law of the microseismic events on the fault in the first mining area of the Pulang copper mine, calculated the cumulative apparent volume and energy index changes of the microseismic events near the fault base, and quantitatively analyzed the microseismic event anomalies under the influence of the fault. The results show that rupture of the rock makes the cumulative apparent volume and energy index change significantly, while the timeliness of both makes the cumulative apparent volume predictive of the occurrence of rock fracture and rockburst, and the number of microseismic events corresponds to the intensity of the fault activation, which plays a predictive and guiding role in the subsequent study of fault activation, stability monitoring, and safe production in the mine area of Pulang copper mine.

Influence of the spatial distribution of underground tunnel group on its blasting vibration response

The spatial distribution of underground tunnels is significant to the stress redistribution in the surrounding rock masses and blast wave propagation. The field blasting tests were first carried out to study the propagation of blast-induced seismic waves through underground tunnels of the Xiluodu Hydropower Station in China. The results show that the peak horizontal particle vibration velocity can be used as a safety criterion for underground tunnels. The effects of in situ stresses and spatial distributions of the tunnel group on the vibration velocities distribution is afterward investigated by numerical simulation. The results show that there is a significant amplification of the blasting vibrations in the adjacent tunnels, which depends on their vertical positions during the excavation of a tunnel. The peak vibration velocity decreases as the lateral separation between tunnels increases. When the separation between the tunnels exceeds the width of three tunnels, the impact of the blast waves on each part of the adjacent tunnel tends to be stable on the whole. In terms of the size of the tunnel, the blasting vibration velocity in the upper part of the straight wall on the front-blast side increases as the width increases (and then levels off), while the blasting vibration velocity in the lower part decreases as the width increases (and then levels off). Finally, a generalized formula of blasting vibration velocity considering the spatial distribution is established, which can well predict the vibration velocity of particles in underground tunnels.

Application of Bayesian Neural Network (BNN) for the Prediction of Blast-Induced Ground Vibration

Rock blasting is one of the most common and cost-effective excavation techniques. However, rock blasting has various negative environmental effects, such as air overpressure, fly rock, and ground vibration. Ground vibration is the most hazardous of these inevitable impacts since it has a negative impact not only on the environment of the surrounding area but also on the human population and the rock itself. The PPV is the most critical base parameter practice for understanding, evaluating, and predicting ground vibration in terms of vibration velocity. This study aims to predict the blast-induced ground vibration of the Mikurahana quarry, using Bayesian neural network (BNN) and four machine learning techniques, namely, gradient boosting, k-neighbors, decision tree, and random forest. The proposed models were developed using eight input parameters, one output, and one hundred blasting datasets. The assessment of the suitability of one model in comparison to the others was conducted by using different performance evaluation metrics, such as R, RMSE, and MSE. Hence, this study compared the performances of the BNN model with four machine learning regression analyses, and found that the result from the BNN was superior, with a lower error: R = 0.94, RMSE = 0.17, and MSE = 0.03. Finally, after the evaluation of the models, SHAP was performed to describe the importance of the models’ features and to avoid the black box issue.

Automatic Identification System for Rock Microseismic Signals Based on Signal Eigenvalues

The microseismic signals of rock fractures indicate that the rock mass in a particular area is changing slowly, and the microseismic signals of rock blasting indicate that the rock mass in a particular area is changing violently. It is of great significance to accurately distinguish rock fracture signals and rock microseismic signals for analyzing the changes in the rock mass in the area where the signal occurs. Considering the microseismic signals of the Dahongshan Iron Mine, the time domain, frequency domain, energy characteristic distribution, and fractal features of each signal were analyzed after noise reduction of the original signal. The results demonstrate that the signal duration and maximum amplitude of the signal could not accurately distinguish the two types of signals. However, the main frequency of the rock fracture signal after noise reduction is distributed above 500 HZ, and the main frequency of the rock blasting signal is mainly distributed below 500 HZ. After the denoised signal is decomposed by the ensemble empirical simulation decomposition, the energy of the IMF1 frequency band of the rock fracture signal occupies an absolute dominant position, and the sum of the energy of the IMF2–IMF4 frequency bands of the rock blasting signal occupies a dominant position. The fractal box dimension of the rock fracture signal is mainly below 1.1, and the fractal box dimension of the rock blasting signal is mainly above 1.25. According to the above research results, an automatic signal recognition system based on the BP neural network is established, and the recognition accuracy of the rock blasting and rock fracture signals reached 93% and 94% respectively, when this system was used.

Sensitivity analysis on blast design parameters to improve bench blasting outcomes using the Taguchi method

In surface mines, bench blasting is a typical way of excavating hard rock mass. Although a significant development has taken place in explosive technology but still only a part of the energy is used to excavate and a large proportion of energy is wasted away and creates a number of nuisances. Backbreak, massive rock fragmentation, and high-intensity ground vibration are all symptoms of improper blasting. As a result, production costs increase significantly while productivity decreases. The blasting outcomes are affected by a variety of factors, which may be classified into three categories: rock properties, explosive properties, and blast geometry. Consequently, it is necessary to examine the effect of these parameters on bench blasting. So, in this study, a sensitivity analysis has been performed on various blast design parameters using the Taguchi method to study the influence of blast design parameters on blast vibration, backbreak, and rock fragmentation. A total of 32 experiments have been designed and numerical modeling was also carried out, using LS DYNA software to simulate the blast results. It was found that the blast hole diameter is the most important factor influencing the blasting outcomes. However, the number of rows in a blast affects backbreak almost slightly more than the hole diameter, but blast vibrations and the surrounding rock damage strongly depend on the hole diameter. Furthermore, rock blast geometry significantly affected rock blast vibration and damage compared to explosive properties. However, both blast geometry parameters and explosive properties play a significant role in backbreaking.

APPRAISAL OF THE ABAJI-ABUJA (NIGERIA) ML 2.25 EARTH-TREMOR OF 10th JANUARY 2020

This research aims at determining the epicentre, magnitude and energy dissipated during the earth-tremor which took place at Abaji-Abuja (Nigeria) on 10th January 2020 at 13:46:20 UTC. The event was recorded by Volksmeter II VMII-2RU broadband Seismographs located at the Earthquake and Space Weather laboratory, Obafemi Awolowo University, Ife, Osun state, Nigeria. The computed P-wave and S-wave arrival times and lag times were 35.8seconds, 36.1seconds and 33.3seconds recorded by three Seismographs Ife (1), Ife (2) and Ife (3) respectively. The WinQuake software was used for the analysis. Epicentre distances computed were 330.3 km, 333.5 km and 303.2 km from the three seismograms, using trilateration method. The results gave the epicentre location at 8049’N and 6047’E (Gurdi town, Yaba District, Abaji LGA, Abuja, Nigeria),focal depth of 5 km, and average epicentral distance of 322.3km from Ile-Ife. The tremor has a Local Magnitude of 2.25 MLand Coda Magnitude of 3.7Md, and the dissipated energy of 149.6 × 10-12 KJ. The implication of these results is that a local magnitude of 2.25 ML of 149.6 × 10-12KJ of energy serves as an indicator to the future occurrence of another earthquake within the said region. Necessary precautionary measures should be taken when carrying out geological and construction works within the Abaji-Abuja environs. The massive rock blasting and quarrying must have reactivated the faults within the area.