New theory for the rock mass destruction by blasting (original) (raw)
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Managing the rock mass destruction under the explosion
Journal of Sustainable Mining
Using the theory of elasticity and the main provisions of the quasi-static-wave hypothesis of the mechanism of the destruction of a solid medium under the action of an explosion, analytical modelling of the parameters of the formation of crumpling zones and crushing of the rock mass around the charging cavity during its explosive loading was carried out. Analytical models of the radii of the crumpling, intensive fragmentation and fracturing zones formed around the charging cavity in the rock mass during its explosive loading, taking into account the pressure of the explosion products, the limit of tensilecompressive strength of the rocks, their structural composition, fracturing and compaction under the action of rock pressure, were developed. Based on the change in the stress-strain state of the rock mass under the action of the explosion, numerical modelling of the radii of the zones of crumpling, intensive fragmentation and fracturing was performed using the finite element method. According to the simulation results, the power dependence of the change in the radii of the crumpling and fragmentation zones of the rock mass was determined depending on the diameter of the charging cavity, the pressure of the explosion products, and the limit of rock compressive strength. By comparing the results of analytical and numerical modelling for rigid boundary conditions of a homogeneous non-cracked rock mass, the difference in the values of the radii of the defined zones was established as being 4, 8 and 6%, respectively. The resulting analytical models of the radii of crushing zones, intensive fragmentation and fracturing increase the accuracy of estimating the parameters of rock mass destruction by explosion by up to 50% and improve the parameters of drilling and blasting operations when carrying out mining operations, special purpose cavities and rocking of the rock mass.
2018
The assessment of fragmentation through blasting and therefore subsequent crushing and grinding stages is important in order to control and optimize the mining operation. Prediction of the mean size of fragmented rock by the rock mass characteristics, the blasting geometry, the technical parameters and the explosive properties is an important challenge for the blasting engineers. Some of the effective parameters on rock fragmentation have been investigated in several empirical models. A model for fragmentation in bench blasting was developed using the effective parameters on the existing empirical models, so as to propose a simple applicable model to predict X50. The proposed model was calibrated by nonlinear fits to 35 bench blasts in different sites from Sungun copper mine, Akdaglar quarry and Mrica quarry. In order to validate the proposed model, its results were compared to data obtained from six blast sites in Chadormalu iron ore mine and one in Porgera gold mine. The results i...
Evidences of the influence of the detonation sequence in rock fragmentation by blasting – Part I
Drilling and blasting are fundamental operations in the mining cycle and constitute an important component of the mining costs. Rock fragmentation can in principle be managed by means of two options: by increasing or reducing the specific consumption of explosives, or by modifying the drilling pattern. The choice of one or other type of control depends on the relationship between the unit costs of drilling and explosives, and on technical restrictions or regulations imposed by different reasons. It is then necessary to identify the link between the blast design and some factors affecting the downstream processing of the product. This paper analyzes the theoretical basis aimed at evaluating the main parameters involved when organizing a production blast in open pit quarries. In particular, a method developed through the analysis of the results in a large number of limestone open pit quarries in Italy is described and commented. The first experimental results in Brazil have been obtained by applying this method at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo. Experimental methods and results will be analyzed and discussed in the second part of this paper.
Numerical investigation of blasting-induced damage in cylindrical rocks
International Journal of Rock Mechanics and Mining Sciences, 2008
In order to investigate rock fracture and fragmentation mechanisms under dynamic loading, a cylindrical rock model with a centralized borehole is developed through the use of AUTODYN code. According to the material properties and loading conditions, four kinds of equation of state (EOS), linear, shock, compaction and ideal gas, are applied to the four kinds of materials employed in this numerical model. A modified principal stress failure criterion is applied to determining material status, and a well-behaved explosive, PETN, and a relatively homogeneous igneous rock, diorite, are used in this rock model. A single centrally located line source of explosive is fired numerically to produce the dynamic loadings operating on the surrounding rocks. This numerical model is applied to actual blasting conditions. The rock failure mechanism under dynamic loading is first analyzed, and then the influences of the following factors on rock fracturing are discussed: (a) coupling medium, (b) confinement, (c) boundary condition, (d) initiation location in an explosive column, and (e) air ducking. The results show that all these factors have significant effects on rock fracturing under dynamic loading. r
A brief history of the development of blasting and the modern theory of rock breaking
Journal of Degraded and Mining Lands Management, 2016
The article is devoted to the task today to improve the effectiveness of blasting during construction of horizontal and inclined mine excavations. Construction of new and reconstruction of existing mines requires large volume of excavation works, which length can reach tens of kilometers for only one project. Drilling and blasting workings allow not only to break out rocks from a frontal part of an excavation, but also cause an internal effect, which can lead to undesired damage that, in turn, often lead to increased expenses for excavation operations and safety problems for personnel. Calculation methods for blasting and explosion operations is a topical issue in mining industry as they allow to improve characteristics of excavation works and safety of explosion operations. Dozens of scientists offer their design, which reflects the vision of the problem and its solution. There are many methods for calculating the parameters of drilling and blasting, but so far not developed a uniform methodology of calculation, which would encompass all the factors and explained the mechanism of formation of cracks around the explosive charge and the process of breaking rock. The paper presents a novel methodology for calculations for blasting and explosion operations. That methodology comprises various specifics of rock geology and mining engineering during works in horizontal and vertical excavations. In this paper given an algorithm for calculation two main areas of destruction: crushed zone and fracturing zone. In addition, article outlines main aspects of Mining Engineering Development from Antiquity until present days and presents the dynamic of mineral resources.
Blasting design for obtaining desired fragmentation
2011
The empirical prediction of expected fragmentation is in most cases carried out by using the Kuz-Ram model. By doing this, the Rosin-Rammler theory is applied. This theory, first proposed by V. M. Kuznetsov (1973), gives a reasonable description of the blasted rock fragmentation. Using this approach, one calculates a rock factor that describes the nature and geology of the rock. The uniformity index is also obtained that characterizes the explosive loading and blast pattern type and dimensions. This allows the characteristic size and size distribution to be calculated according to the Rosin-Rammler procedure. Due to the amount of too many input rock mass parameters, that are not unambiguously determined, the rock factor may also not be satisfactory and this unfavorably influences the fragmentation prediction. The later work of others, particularly that of Lilly (1986) and Cunningham (1983, 1987) was useful for improving the efficiency of that approach. The authors have developed the...
Evidences of the influence of the detonation sequence in rock fragmentation by blasting – Part I
Rem: Revista Escola de Minas, 2015
Drilling and blasting are fundamental operations in the mining cycle and constitute an important component of the mining costs. Rock fragmentation can in principle be managed by means of two options: by increasing or reducing the specific consumption of explosives, or by modifying the drilling pattern. The choice of one or other type of control depends on the relationship between the unit costs of drilling and explosives, and on technical restrictions or regulations imposed by different reasons. It is then necessary to identify the link between the blast design and some factors affecting the downstream processing of the product. This paper analyzes the theoretical basis aimed at evaluating the main parameters involved when organizing a production blast in open pit quarries. In particular, a method developed through the analysis of the results in a large number of limestone open pit quarries in Italy is described and commented. The first experimental results in Brazil have been obtained by applying this method at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo. Experimental methods and results will be analyzed and discussed in the second part of this paper.
2024
In quarries and mines, the drilling and the blasting activities is an essentially fundamental way of excavating rock. The blasting process is an integral and important part of mining operations and is intrinsically destructive for a variety of different reasons, notably efficiency, cost effectiveness and the capacity to shatter away even the most solid rock. The primary and main purpose of designing a blast pattern in an open pit or quarry is to use quantities of explosives to fragment the rock material down to smaller pieces and shapes that can make it easier to carry out various subsequent operations such as excavation, charging, transporting, crushing, grinding etc. The conception of a blasting model depends on two sorts of variables: firstly uncontrollable factors, such as the geological structure and the properties of the rock mass. Secondly controllable factors, such as the geometric model (height of the bench, length of the charge, diameter, spacing, burden, stemming length, etc.), the properties of the explosives used (type, resistance, energy, etc.) and the temporal parameters (time delay and initiation sequences). The different fragmentation blasting analysis procedures have inherent difficulties, which result in varying levels of accuracy. Consequently, each technique is adapted to a particular purpose. This research assessed and then compared the particle size distribution of limestone rocks from the New Cement Quarry (NCQ) at Setif-NE Algeria, using the Wip Frag computer imagery processing program and one of the empirical models called Kuz-Ram. Three blasts from the quarry, using different mesh designs in terms of load and spacing (rectangular, square and triangular) analyzed using the two methods. The design parameters of the blast obtained and evaluated as input to the Kuz-Ram model. Pictures of the pile taken and downloaded to the Wip Frag software for analysis. The obtained results in the case of a change in the geometrical parameters of the explosion show that a significant reduction in the size of the oversized products observed by the numerical method. Furthermore, in this study, the ratio between the spacing and the charge in the case of the triangular pattern has a major influence on the size of the fragments and makes it possible to make optimum use of the distribution principle and the amount of energy of the explosive.
Having indicated the importance of blasting in mining and introducing some of numerous researches that have increased the level of understanding the mechanisms of rock breakage by explosives, a wellknown assertion that there are no blasting models based on constitutive relationships describing the rock fracture has been repeated. The blasting model based on constitutive relationships has been introduced. The formations of the radial tension cracks around blast holes have been explained. The separations of the zones with different densities of radial cracks have been proposed, and then it has been shown the usage of the radius of the radial cracks zones for the design of the blasting pattern.
Three dimensional numerical rock damage analysis under blasting load
Tunnelling and Underground Space Technology, 2013
In this study, the behaviour of rock mass subjected to blasting load is investigated using three dimensional finite difference numerical modelling. In the analyses, Mohr-Coulomb failure criterion has been used for the characterisation of the rock mass strength. Stresses acting on the borehole boundary have been simulated by an exponential function which reaches its maximum within a short time and then falls to zero value in a considerable period. The strain rate effect on the mechanical properties of rock material has also been taken into account in the analyses. Different explosive and site conditions have been studied to investigate the effects of loading rate and anisotropic high in situ stresses on blasting performance and blast induced damage zones. Results have shown that the most efficient explosive in rock blasting will be the one with low frequency content but with a sufficiently high borehole wall pressure. In addition, it has been verified that the directions and the magnitudes of major principle stresses affect the development of the crack zone around the borehole. Finally, it has been seen that proposed equation for the dynamic compressive strength of rock material fits very well to general suggestions.