Single Blasthole Research Articles

A Case Study of Fragmentation Improvement by Primer Placement in Kevitsa Mine

The effect of detonator placement on rock fragmentation by blasting was studied in the Kevitsa open-pit mine. Considering rock mass properties, explosives properties, and blast parameters, a comprehensive analysis of 37 production blasts confirms that the middle detonator yields finer fragmentation than the bottom detonator in the full range of investigated sizes. Meanwhile, using the LS-DYNA code, a bench model with a single blasthole was built in a three-dimensional setting. A single detonator placed at two different positions—the middle and bottom—of the explosive column was analyzed in this study. By analyzing principal stress states on the plane through the blasthole axial and vertical to the bench face, the numerical results show that the middle detonator creates a stress concentration area near the bench face characterized by triaxial tension, while the bottom detonator does not. Furthermore, the middle detonator generates a larger stress concentration area with biaxial tension near the bench face than the bottom detonator. Considering that triaxial and biaxial tensions are more favorable to fragmentation than uniaxial tension, it can be concluded from simulation results that these areas with triaxial tension and biaxial tension in the middle detonator are a significant factor contributing to achieving better fragmentation, compared to the bottom detonator. The middle detonator position has replaced the bottom detonator position in the Kevitsa mine.

Breaking the natural jointing by a single blasthole charge

Breaking the natural jointing by a single blasthole charge

Damage analysis and safety control of surrounding rock around peripheral hole of diversion tunnel

The control of overbreak in blasting excavation is a significant technical challenge and a subject of extensive research in the field of engineering. This study examines the damage characteristics of the surrounding rock in a tunnel section through blasting test and numerical simulation conducted as part of the San Gavan diversion tunnel project in Peru. The orthogonal test of peripheral holes under the influence of explosive spacing, blasthole spacing and smooth blasting layer thickness was designed to analyze the characteristics of rock damage under different parameter combinations and the influence of various factors on rock damage. Based on the USBM formula, this paper deduces a mathematical model considering blasthole spacing and explosive spacing to predict the rock damage range. The main conclusions are as follows: on the tunnel section, the average damage range of vault and arch springer is slightly larger than that of spandrel and haunch. For a single blasthole, the rock damage range in different sections is: explosive > air > stem, and the degree of rock damage at the bottom of blasthole is the highest. Smooth blasting layer thickness has a significant effect on rock damage rate on the side of non-reflect boundary. When smooth blasting layer thickness is 45 cm and 55 cm, the boundary conditions of numerical model have a significant effect on the rock damage. The reflection of blasting stress wave on the free surface leads to the further increase of rock damage range. The blasthole spacing and explosive spacing have a significant effect on rock damage range on the side of non-reflect boundary, and both show a negative correlation. Based on the prediction model of rock damage, the combination of peripheral hole parameters satisfying the standard is obtained, which provides guidance for blasting design.

Experimental Investigation of Blast‐Induced Crack Propagation Based on Digital Image Correlation Analysis

Blasting is widely used in civil and mining engineering projects, with the side effect of introducing damage to the remaining rock. The damage can be differentiated from the cracks in the remaining rock, which increases the concerns of safety and requirements for rock support. In situ study of crack development remains complicated and costly; therefore, small‐scale blasting experiments are a viable alternative for a detailed investigation of the crack propagation behavior. To fill the gap, this study examined a small‐scale blasting test by investigating the velocity of the cracks implementing the digital image correlation (DIC) technique and avoiding contact methods such as strain gauges. An ultra‐high‐speed camera (UHSC) was used to record the blasting test in a single blasthole rock‐like sample with a PETN cord. The experimental design underwent calibration until achieving the configuration of the equipment while ensuring the safety distance. The developed experimental methodology was tested successfully capturing the crack behavior. The analysis outcomes showed that the raw UHSC data needed to be preprocessed to enhance the tracking of cracks with the DIC method. The findings of the DIC data analysis indicated a fluctuation in the propagation velocity along the cracks (889–1129 m/s), revealing that the proposed methodology positively contributes to the propagation behavior of using the DIC method to track the blast‐induced cracks.

Solving the Lamé problem in the quasi-brittle setting to substantiate the solution scheme for rock breaking by the blast-hole method

Introduction. The blast-hole method of mining and preparing rocks for excavation has been used by mankind since ancient times. However, there are no generally accepted and generally recognized design and calculation methods for this process, which was established in the review part of this work. Research objective is to develop a basic analytical model for hard rock quasi-brittle materials breaking by a blast-hole method using static thrusts. Methods of research. A detailed analysis of the breaking mechanism through the transition state from the rock material continuity to its separation is the methodological basis of the developed quasi-static model for calculating the energy-power indicators of the process of separating volumes (pieces) of rock into separate parts. It makes it possible to justify and determine: the irreversible energy of rupture through the energy constant rock material in relation to the process energy efficiency, critical load resulting in local breaking, the size and number of the primordial tension cracks, as well as the number of through cracks. Result. The obtained indicators and parameters formed the body of the energy balance equation of the irreversible energy of rupture of rock pieces. The developed methodology for setting and solving the problem of the limiting state of quasi-brittle materials rupture in the form of a thickwalled cylinder (the Lamé problem) that simulates a certain solid volume deformed by a uniformly distributed blast-hole pressure of thrusts, is universal and can serve as a base for assessing a set of issues related to mining. The resulting interrelation of indicators made it possible to derive an equation for the energy balance of the rock volumes rupture. Due to the solution for this equation, the critical value of the blast-hole pressure that results in local breaking, the size of primordial cracks, and the corresponding limiting burst pressure were obtained for the first time. Theoretical novelty. Within the framework of the general approach of the quasi-brittle materials breaking linear theory, based on the developed methodology, the problem of the limiting state of the rock in the form of natural joint loaded with a static thrust through a single blast-hole, was correctly stated and solved by the energy method for the first time. As a result of the research, an analytical dependence of the rock static breaking energy intensity was obtained, which includes both the volumetric specific energy of potential deformation and the specific surface energy

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%.

Horizontal single hole blast testing – Part 1: Systematic measurements using TLS surveys

Large scale Single Hole Blast (SHB) testing is used to characterize blasting behavior in a cost-effective manner. SHB testing provides the means to assess the effect of blasting specifications (e.g. burden dimension, explosive used, borehole diameter) on rock cratering and blast efficiency. The observed behavior depends significantly on the testing procedure and measurements recorded. Crater characteristics are commonly described by the displaced volume of rock and breakout shape. Analysis of SHB test results relies on reproducible measurements.This paper proposes a method for analysis of horizontal SHB tests using data collected via terrestrial laser scanning (TLS) surveys. The procedural algorithms, point cloud manipulations, and analysis facilitate systematic SHB testing, including the use of a reference axis aligned with the blasthole orientation. The definition of crater extents, absolute burden measurements, methods for crater slicing, and filtering are developed to maintain consistency with the plane strain assumption. Crater partitioning protocols are elaborated to enhanced details of captured data. A detailed workflow of the analysis is provided with examples from compiled field testing. The conventional SHB measurement approach for crater breakout angle is refined to account for superficial surface roughness, and to capture the full crater shape. Data captured for the craters is represented along the blasthole length to capture the plane-strain component of single blasthole cratering. Comprehensive results from full scale field experiments are presented in a companion paper.

Research on improved rock blasting damage constitutive model considering compression-shear damage

It is of great importance to study the proper rock blasting damage constitutive model for the design of rock blasting excavation parameters and the damage assessment of retained rock. Therefore, on the basis of the classic KUS rock damage constitutive model which only involved tensile damage, considering the compression-shear damage of rock near the explosion source caused by extensive blasting load, an improved rock blasting damage constitutive model is established. Meanwhile, the distribution of rock damage zone of a single blasthole is calculated by dynamic finite element software based on the improved model, and the results show that the ratio of crushing zone radius to cartridge radius is between 4.3 and 4.6 under different charging radius, while the ratio of fracture zone radius to cartridge radius is between 78.9 and 83.8, which is close to the existing research results. Thus, the accuracy of the established constitutive model of rock blasting damage is verified.

River-ice blasting and explosive weight optimization for ice-flooding mitigation: A case study

Ice blasting with explosives before the spring breakup of river sections is a preventive measure for ice flooding. Based on 496 datasets on ice cover blasting with No. 2 emulsion rock explosives measured in the Mohe reach of the Heilongjiang River from 2015 to 2018, we analyzed the relationships between the blasting-crater diameter and water depth below the ice and between the blasting-crater diameter and the explosive-placement depth below the ice. Further, we analyzed the functional relationship between the explosive weight of a single blast hole and the blasting-crater diameter. Based on the above analysis we proposed an equation to calculate the minimum blasting cost for the same blasting effect. Using a 5-km section of the Heilongjiang River as an example, the proposed optimization method can save ~46% of the total blasting cost while achieving the same blasting effect. Through prototype observations of the Longdao Wharf and the Shengdan Village sections of the Mohe reach, Heilongjiang River, we confirmed that ice blasting can significantly accelerate the melting of ice. Moreover, data records showed that no significant ice-jam flooding has occurred in this section of the Heilongjiang River during the spring ice breakup period in the past five years of consecutive blasting.

Numerical modeling of the fractured zones around a blasthole

The high-energy rate of shock waves, as an important part of explosion energy, plays a significant role in the mechanism of rock fragmentation. This energy rate and the mechanism of rock fracturing are controlled by several parameters related to both the explosive charge and rock mechanical properties. In this study, the mechanism of rock fragmentation due to blast-induced shock waves in a single blasthole was numerically simulated by a two-dimensional discrete element code. The numerical results included the stresses around the blastholes, the number of blast-induced fractures and the density of cracks, which were compared with the corresponding experimental results. This comparison showed that the numerical results were in good agreement with their experimental counterparts. It is concluded that the proposed numerical model could be effectively used for the simulation of the crack propagation process around a blasthole.

Approximate models of blast vibration in non-isotropic rock masses

It is well known that variations in the local geology of rock masses will influence the transmission of blast vibration. For example, the vibration within a jointed rock mass will depend upon the number and spacing of joints as well as the joint orientations. As another example, the vibration within any rock that exhibits a seismic velocity anisotropy will depend upon the degree of velocity variation in given directions. The present work describes approximate models for the transmission of blast vibration in such rock masses. These models consist of two components. The first component is a Dynamic Finite Element Model (DFEM) to describe the radiation of a single blasthole in the particular geology of interest. The second component is a Monte Carlo waveform superposition model (MCWSM) to account for a delayed sequence of such blastholes within a rock mass. This combined DFEM-MCWSM approach predicts that the vibration depends upon the direction of blast hole initiation with respect to the strike direction of geological features. If the angle between these two directions is chosen carefully, then the vibration can be reduced. This allows for the selection of appropriate delay sequences to minimise blast vibrations within the local geology, and is thus clearly relevant to wall control blasting.

NUMERICAL STUDY OF THE FRACTURING MECHANISM AROUND A BLASTHOLE AND INVESTIGATING THE EFFECT OF DISCONTINUITIES ON THE FRACTURE PATTERN

The mechanism of rock fragmentation around blastholes is of prior importance in the evaluation of drilling and blasting performance in open pit and underground mines. This paper aims to numerically investigate the crack propagation mechanism around a single blasthole using the distinct element method (DEM). In this study, two specimens with different borehole diameters were considered and the effects of the stress waves on their cracking mechanism were simulated. To validate the numerical model, the length of the radial cracks around each blasthole was measured and compared against an analytical fracture mechanics model. The fractured zones around the blasthole were also compared against previous experimental tests and good agreement was observed. The effect of a single discontinuity on the crack propagation mechanism was also studied and it was found that the discontinuity normal stiffness plays a significant role in the fractured zones around the blasthole. For low values of normal stiffness, the discontinuity surface acted as a free surface, and the shock wave was significantly reflected, while at high values of normal stiffness, cracks propagate across the discontinuity surface.

Synthesis of single-hole signatures by group delay for ground vibration control in rock blasting

Prediction and control of ground vibrations become essential as with the development of neighborhoods in the proximity of active mining operations or the need for new infrastructure in urban centers, both requiring the use of blasting. Novel ground vibration prediction models attempt to reproduce a whole vibration waveform from a blast and are based, in most cases, on the collection of vibrational information from a single blasthole. A single blasthole should have the same characteristics (geometry and weights of explosives) as the blastholes used in production shots. In some cases, the collection of the fundamental information (the signature) is straightforward. In more complex cases, the fundamental information from ground vibration data is collected from previous production shots. This study presents a novel methodology to assess the fundamental ground vibration information (the signature) using known information such as one event waveform (a production shot waveform) and the timing sequence used (the comb function) for the shot. The methodology is based on the analysis of group delay, a concept widely used in signal processing, and is modified here for the analysis of ground vibration waveforms. The methodology is developed using real data collected in coal and quarry mining operations, and at the end of this document, one case study with step-by-step calculations is presented to show the benefits of the methodology.

Numerical simulation of stress wave interaction in short-delay blasting with a single free surface.

It is generally believed that stress wave superposition does occur and plays an important role in cutting blasting with a single free surface, in which explosive columns of several blast holes with short spacing are simultaneously initiated. However, considering the large scatter of pyrotechnic delay detonators that are used in most underground metal mines in China, the existence of stress wave superposition and the influence of this effect on rock fragmentation are questionable. In the present study, the stress wave interaction in short-delay blasting with a single free surface was studied through the use of the LS-DYNA code. Stress waves induced by two blast holes blasting with different delays were compared with the single blast hole case, and the effects of delay time, detonating location and spacing on stress wave superposition were investigated. The numerical results showed that for blast holes with a 1 m spacing, stress wave interaction only occurs when the delay time is 0 ms and does not occur for blasting with delays of more than 1 ms. An increase in the duration of a stress wave via optimizing the detonation location does not improve the stress wave interaction. For a 1 ms delay, stress wave superposition only occurs when the spacing is more than 4 m, which is a rare case in practice. The results indicated that the occurrence of stress wave superposition for blasting with a single free surface is strictly limited to conditions that would be difficult to achieve under the existing delay accuracy of detonators. Therefore, it is unrealistic to improve fragmentation via the stress wave interaction in field blasting. Furthermore, the numerical results of the stress wave interaction also show that there would be a great potential to reduce the hazardous vibrations induced by short-delay blasting by using electronic detonators with better control of delays in an order of several milliseconds.

Determination of equivalent blasting load considering millisecond delay effect

In the analysis of the effects of rock tunnel blasting vibration on adjacent existing buildings, the model of simplified equivalent load produces higher calculation result of vibration, due to the lack of consideration of the millisecond delay effect. This paper, based on the static force equivalence principle of blasting load, proposes a new determination method of equivalent load of blasting vibration. The proposed method, based on the elastic-static force equivalence principle of stress wave, equals the blasting loads of several single blastholes in the same section of millisecond blasting to the triangle blasting load curve of the exploded equivalent elastic boundary surface. According to the attenuation law of stress wave, the attenuated equivalent triangle blasting load curve of the equivalent elastic boundary is applied on the tunnel excavation contour surface, obtaining the final applied equivalent load. Taking the millisecond delay time of different sections into account, the time-history curve of equivalent load of the whole section applied on the tunnel excavation contour surface can be obtained. Based on Sailing Tunnel with small spacing on Sanmenxia-Xichuan Expressway, an analysis on the blasting vibration response of the later and early stages of the tunnel construction is carried out through numerical simulation using the proposed equivalent load model considering millisecond delay effect and the simplified equivalent triangle load curve model respectively. The analysis of the numerical results comparing with the field monitoring ones shows that the calculation results obtained from the proposed equivalent load model are closer to the measured ones and more feasible.

Study on the efficiency of destress blasting in deep mine drift development

Canadian hard rock mines continue to reach deeper deposits, which poses greater challenges to mine safety including rock burst control. Destress blasting techniques have been successfully employed in such underground mines with the aim of preconditioning highly stressed rock mass to mitigate the risk for rock burst occurrence in deep mines. In the present study, the efficiency of destress blasting is examined through a comparison between traditional and alternative numerical modelling approaches. The traditional modelling approach assumes a uniformly distributed blast-induced damage zone extending over the entire drift face, whilst the alternative modelling approach, presented herein, simulates the damage zone for each individual blast hole. In the first part of this paper, a three-dimensional numerical model of a single blast hole is constructed, whereby the extent of blast-induced damage zone is delineated. The latter part of this paper uses the single-hole model results to examine the efficiency of destress blasting as practiced in drift development in deep mines. It is demonstrated through comparison of FLAC3D numerical simulation results that the traditional modelling approach may lead to an overly optimistic indication of destress blasting efficiency when compared with the alternative modelling approach, in which a more precise simulation of the damage zones is applied.

Basic trends in development of drilling equipment for ore mining with block caving method

The authors have determined the causes of drop in performance of induced block caving using fans of blastholes 105 mm in diameter and single blastholes 250 mm in diameter, as well as the sources of increased drilling cost and expansion of start-up time of production blocks in Abakan underground mine. Alternatives of improvement in drilling efficiency under current conditions are discussed.

Dynamic Modelling of Fault Slip Induced by Stress Waves due to Stope Production Blasts

Seismic events can take place due to the interaction of stress waves induced by stope production blasts with faults located in close proximity to stopes. The occurrence of such seismic events needs to be controlled to ensure the safety of the mine operators and the underground mine workings. This paper presents the results of a dynamic numerical modelling study of fault slip induced by stress waves resulting from stope production blasts. First, the calibration of a numerical model having a single blast hole is performed using a charge weight scaling law to determine blast pressure and damping coefficient of the rockmass. Subsequently, a numerical model of a typical Canadian metal mine encompassing a fault parallel to a tabular ore deposit is constructed, and the simulation of stope extraction sequence is carried out with static analyses until the fault exhibits slip burst conditions. At that point, the dynamic analysis begins by applying the calibrated blast pressure to the stope wall in the form of velocities generated by the blast holes. It is shown from the results obtained from the dynamic analysis that the stress waves reflected on the fault create a drop of normal stresses acting on the fault, which produces a reduction in shear stresses while resulting in fault slip. The influence of blast sequences on the behaviour of the fault is also examined assuming several types of blast sequences. Comparison of the blast sequence simulation results indicates that performing simultaneous blasts symmetrically induces the same level of seismic events as separate blasts, although seismic energy is more rapidly released when blasts are performed symmetrically. On the other hand when nine blast holes are blasted simultaneously, a large seismic event is induced, compared to the other two blasts. It is concluded that the separate blasts might be employed under the adopted geological conditions. The developed methodology and procedure to arrive at an ideal blast sequence can be applied to other mines where faults are found in the vicinity of stopes.

Numerical simulation of rock mass vibrations induced by nearby production blast

It is of importance to understand the effect of production blasts on the surrounding rock formations in underground mines. This study presents a numerical procedure to simulate stress waves resulting from nearby production blasts. First, the damping coefficient and peak borehole pressure are calibrated using a dynamic numerical model of a single blast hole. The resulting time-varying particle velocities in the surrounding rock mass at the specified points are calculated. These are then used as input parameters in a three-dimensional mine-wide model, considering a positional relationship between the blast hole and the specified points on the wall rock. The mine-wide model encompasses a fault running parallel to a steeply dipping, tabular ore deposit. Dynamic analysis simulating the effect of production blasts is conducted after the extraction of mining blocks with static analysis. In this study, variations of stresses along the fault due to blast-induced stress waves are examined. Results demonstrate that the developed methodology can reasonably simulate stress changes induced by stress waves on the fault. The methodology considers blast sequences and time-varying blast loads that vary according to the positional relationship between the blast holes and the specified points on the wall rock.

Distinct Element Modeling of the Effect of Joint Persistence on Dynamic Fracturing of Jointed Rock Masses

Rock masses consist of intact rock and discontinuities such as faults, joints and bedding planes. The presence of such discontinuities in rock masses dominates the response of jointed rock masses to static and dynamic loading. These structural weak planes seriously hinder and affect the propagation of stress waves in rock mass. The joints parameters such as persistence, orientation, distribution patterns, spacing and filling material have a significant effect on the response of rock masses against wave propagation. In most studies of blast induced wave propagation in jointed rock mass, it is assumed that joints are continuous. In many situations the rock mass consists of non-continuous joints and rock bridges. Rock bridges and discontinuous joints have a different effect on wave and fracture propagation in a blasting operation. With regard to complexities associated with rock blasting in particular in jointed media, numerical tools are viable alternatives for rock blasting analysis. In this study the DEM methods was employed to investigate the effects of rock bridges on the wave propagation process. A plain strain 2D scenario was assumed and a single blasthole explosion was simulated. Three models with different jointing orientation patterns including jointing pattern parallel to free face, perpendicular to free face and orientated at 45 degree with respect to free face were analyzed numerically to investigate rock mass fracturing while blast wave propagation. The discontinuous joints were considered to be filled with weak materials (open joints) and rock bridges are composed of intact rock. In order to allow material plastic failure, a Mohr-Coulomb material model was used. The analysis results show that the stress concentration at the rock bridge location leads to excessive fracturing. This effect is more visible at the free face where the stress wave reflection occurs. Moreover, the obtained results show that the pattern and orientation of non-continuous joint system has a pronounced effect on rock fragmentation.