Rock Directed Breaking Under the Impulse Load

International Journal of Rock Mechanics and Mining Sciences, 2007

To investigate the dynamic fracture mechanism related to blast-induced borehole breakdown and crack propagation, circular rock models containing a single centrally located source of explosive were numerically blasted using the AUTODYN 2D code. According to the material properties and loading conditions, four kinds of equations of state, linear, shock, compaction and ideal gas, are used. A modified principal stress failure criterion is applied to determining material status. The dynamic stresses at the selected target points in a rock sample are computed as a function of time following application of explosive load. It is shown that shear stress (resulting from intense compressive stress) causes a crushed zone near the borehole, the major tensile principal stress causes radial cracks, and the reflected stress wave from free boundary causes circumferential cracks some distance away from the free boundary. The influences of the factors of boundary condition, coupling medium, borehole diameter, decoupling and joint on rock dynamic fracture are discussed. r

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.

Shock and Vibration, 2018

Blast induced rock mass damage and crack propagation play important roles in structure safety and stability in mining, quarrying, and civil constructions. This paper focuses on the effect of small blasthole diameter blast on crack propagation and damage accumulation in water-bearing rock mass containing initial damage composed of inherent geological discontinuities and previous multiblast induced damage. To elucidate this effect, theoretical analysis of calculation method for several important blast influencing factors is firstly presented. Secondly, definition of a practical damage variable using ratio of longitudinal wave velocity in rock mass before blast occurrence to that after blast occurrence and derivation of a damage accumulation calculation equation accounting for initial damage and blasting effect are described. Lastly, a detailed description of the conducted in situ blast tests and plan layout of the sonic wave monitoring holes is reported. The results indicate that blas...

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.

To develop a new theory for the rocks destruction by blasting using a description of the formation processes of zones with various mass state around the charging cavity. Methods. The new theory for the rock mass destruction by blasting has been developed based on the use of the well-known elasticity theory laws and the main provisions of the quasi-static-wave hypothesis about the mechanism of a solid medium destruction under the blasting action. The models of zones of crumpling, intensive fragmentation and fracturing that arise around the charging cavity in the rock mass during its blasting destruction, depending on the physical and mechanical properties of the rock mass, the energy characteristics of explosives and the rock pressure impact, have been developed using the technique of mathematical modeling. Findings. Based on the mathematical modeling results of the blasting action in a solid medium, the mathematical models have been developed of the zones of crumpling, intensive fragmentation and fracturing, which are formed around the charging cavity in a monolithic or fractured rock mass. Originality. The rock mass destruction by blasting is realized according to the stepwise patterns of forming the zones of crumpling, intensive fragmentation and fracturing, which takes into account the physical and mechanical properties of the medium, the energy characteristics of explosives and the rock pressure impact. Practical implications. When using the calculation results in the mathematical modeling the radii of the zones of crumpling, intensive fragmentation and fracturing in the rock mass around the charging cavity, it is possible to determine the rational distance between the blasthole charges in the blasting chart, as well as to calculate the line of least resistance for designing huge blasts.

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.

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

Blasting is a powerful excavation method in terms of both production efficiency and economical costs, but its high environmental impact due to noise, vibrations, and potential damage to surrounding structures may limit its extensive application. The use of explosives as excavation tool is usually ruled by the national codes of practice, in which tolerable limits for induced motion are given for the different structure classes. In order to predict the vibrations induced in the ground at a given distance from the blast centre, attenuation laws, derived from either in situ measurements or analytical solutions of simple elastic wave propagation problems, are adopted. As the attenuation laws usually refer to homogeneous continua, they may not be adequate as a predictive tool for complex geological sites. In such cases, numerical analysis provides a valuable alternative, as the whole propagation history of stress waves could be simulated in principle, irrespective of the geological complexity of the specific site. To describe the progressive effects of underground blasting on the surrounding site, a finite element approach is presented. The explosion energy is translated in a time history of pressure at the boundary of the blast hole. Cracking of the nearby rock mass is modelled according to a cohesive crack model, while elastic behaviour is assumed for the non cracked rock mass and soil deposits. Propagation of stress waves from the blast hole is simulated by a time domain 3-D finite element analysis, which is able to provide the time history of all the relevant quantities describing the motion at any given distance. The numerical results can be post processed in order to derive attenuation laws for the most relevant quantities to which the codes of practice usually refer to, i.e., peak particle velocity and principal frequency of the vibration. The model is energy-conserving, thus the energy supplied by the explosive is correctly partitioned into fracture energy of the rock mass close to the blast hole, elastic energy providing the stress wave propagation and kinetic energy of the fragmented rock blocks. Numerical simulations of two literature case-histories are presented, and the numerical results are compared to the available experimental data. Experimental peak particle velocity could be captured remarkably. Principal frequencies for the rock mass could be reproduced as well. In layered sites, the ratio between the stiffness of the different media where stress waves propagate seems to play a key role in the determination of principal frequencies, while less influence is observed on peak particle velocities.

Bulletin of the Polish Academy of Sciences Technical Sciences

A study of dolomite rock material failure using a simple small-scale blast setup is presented. Laboratory tests were conducted using disc specimens drilled with a borehole in the center. A detonation cord and a blasting cap were fitted inside the borehole to induce cracking and fracturing of the specimens. The specimens were inserted between two steel plates, which were compressed against the specimen using bolt screws. Prior to testing, the most suitable screw torque for constraining the vertical displacement of the specimen surfaces without compressing the specimen was selected based on numerical simulations. Then, the experimental tests with the blasting cap were simulated using the Johnson-Holmquist II (JH-2) material model, and the properties of the blasting cap were determined and verified in two special tests with a lead specimen. Possessing the validated model, the influence of specimen thickness on the cracking patterns was finally analyzed. This paper presents a relatively easy method for studying rock material behavior under blast loading and for validating the numerical and constitutive models used for rock simulations.

International Journal of Engineering & Technology

Finding a new oil well is a stimulating experience at all levels, however, it’s only an important milestone on the road towards exploiting oil and gas. When it comes to well drilling, the condition of the ground that surrounds the oil plays a major role. While there are many factors that dictate the success of exploring and drilling wells, porosity and permeability of the surrounding stone are some of the most important components.This paper focuses on the effective way to increase the porosity and the permeability of the rock using explosives without damaging the rock. In order to reach our aim, a numerical simulation was conducted. In fact, a 2D distinct element code was used, and 4 models were constructed; in each model the number of explosives increase while the blast load per explosive decreases.The dynamic stresses, and velocity vectors of the wave propagation were analyzed to evaluate the behavior of rock masses in each model. Moreover, a grid of history points was studied in...