What is spacing in minning

See Fig. The coarser fragments originate from the first row and from the uncharged zone in the upper part of the blast. Secondary fragmentation may be increased by a plough shaped firing pattern. Fragmentation is also influenced by the original fracturing of the rock.

This applies both during the detonation and in the following operations, such as loading, transportation, crushing and placing of the rock.

These are:. In other words, Toe problem is greatly resolved with Inclined Drilling. The weakness planes are recognised by little or no shear strength along the planes. Typical discontinuity features are:. Fracturing is characterised by rate of fracturing type and frequency as well as orientation angle between blast direction and weakness planes.

Various rock classification systems can be used to characterize the fracturing of the rock mass. They more or less measure the same rock parameters. Increased fissure joint degree gives better blastability. This is typical in regional metamorphic rock types.

Systematically oriented joint sets make the rock more difficult to blast. Large blocks are isolated in the throw without being crushed. Fractured conditions are characteristic for rocks in surface blasting.

In special cases, the bench face direction may be fixed in a non favourable direction due to topography, quarry borders or strict geometrical demands, as in road cuttings or building sites. In these cases, the firing pattern can be used to control the blast direction in a more favourable direction and improve the blasting result.

Before drilling, the blast direction should be set according to the orientation of the main jointing systems. Fragmentation, backbreak and toe problems are all dependent upon the blasting direction. Even though optimal fragmentation usually is the most important criterion, consideration of back wall, toe and bench floor must be considered to get an optimal total result.

Orientation of the back wall may be along a weakness plane and the blast direction turned close up to the optimal angle. Quarry management should provide documentation of the main discontinuity systems in operational maps. The blasting results should be followed up according to blasting directions and main fracture systems.

The results from these studies will be the foundation for further blast planning and optimal quarry management. Some of the most common combinations of rock type, fracturing and conventional quarrying blasting results are discussed. Anisotropy of the rock gives directional dependent rock strength and directional dependent blasting effects. Blast direction is defined to be perpendicular to the bench wall face.

Bench wall direction is described by A, B, C or D. Gas venting along schistosity in the walls. Flyrock and blocks is normal, particularly in the first row. Spacing must be reduced in the first row to reduce these problems.

Blast direction C is most favourable. The best result will appear with blast direction perpendicular to C and back wall along D. In such rock types, the bench floor conditions often will be the main parameter when designing the drilling pattern. The main problem with inclined schistosity is the fact that the most favourable blast direction B is parallel to the strike direction.

When firing row by row, the face does not become stiff enough and it will have excessive buckling. In fissure fractured rock, C is the most favourable orientation when it comes to blast direction and the back wall. Independent upon blasting direction, hole deflection may be a considerable problem in inclined schistose rock, resulting in zones with poor fragmentation and bench floor problems. Approximately vertical fracturing and little anisotropy Typical rock types are quartzite and granite gneiss :.

Rough and uneven back wall. The face gets more uneven with higher fracturing degree, increased drill hole diameter and drill hole pressure. This results in more blocks in front of the rock pile. Backbreak can be reduced by increasing the uncharged length in the back row. Gas pressure leakages in the face resulting in flyrock, poor fragmentation especially along the bench floor and general bench floor problems. Especially in joint fractured rock. Bench floor problems may occur if the first row breaks poorly.

A possible way to make this better is to drill along D and fire along C. A large amount of block from the uncharged length in exfoliated, joint sheeted rock. If blasting on terrain bench, the top should dip backwards, otherwise many blocks will mix into the charged part of the rock pile.

This is definitively the least favourable blast direction in joint fractured rock. C is the most favourable orientation if the back wall and the first row breaks properly. If not, less specific charge in the back row and smaller hole spacing in the first row will improve the result.

Bench floor problems are reduced with increased subdrilling. Necessary subdrilling depends on dip angle. To some extent, hole deflection may reduce the fragmentation degree and increase the bench floor problems. Explosives Energy Release and Rock Breakage: Mechanism of rock breakage while release of Explosives energy upon detonation and other relevant points are discussed below: When an explosive charge is detonated, chemical reaction occur which, very rapidly changes the solid or liquid explosive mass into a hot gases.

This reaction starts at the point of initiation where detonator is connected with explosives and forms a convex like shock wave Compressive wave on its leading edge that acts on the borehole wall and propagates through the explosive column. Ahead of the reaction zone are undetonated explosive products and behind the reaction zone are expanding hot gasses.

Understanding theory of detonation of explosives — The self-sustained shock wave produced by a chemical reaction was described by Chapman and Jouquet as a space. This space of negligible thickness is bounded by two infinite planes — on one side of the wave is the unreacted explosive and on the other, the exploded gases as shown in the Fig. There are three distinct zones:a The undisturbed medium ahead of the shock wave,b A rapid pressure at Y leading to a zone in which chemical reaction is generated by the shock, and complete at X,c A steady state wave where pressure and temperature are maintained.

This condition of stability condition for stability exists at hypothetical X, which is commonly referred to the Chapman- Jouquet C-J plane. Between the two planes X and Y there is conservation of mass, momentum and energy. Fig — 1 Velocity of detonation VOD of explosive is function of Heat of reaction of an explosive, density and confinement.

In other words, faster the detonation velocity of the explosive, quicker is the energy applied to the borehole wall, and for a shorter time period. Conversely, with a slower detonation velocity, the energy is applied more slowly, and for a longer time period. The degree of coupling between the explosive and the borehole wall will have an effect on how efficiently the shockwave is transmitted into the rock. Pumped or poured explosives will result in better transmission of energy than cartridge products with an annular space between the cartridge and the borehole wall.

Again, the pressure that builds up in the borehole depends not only upon explosive composition, but also the physical characteristics of the rock. Strong competent rock will result in higher pressures than weak, compressible rock. When the shock wave reaches the borehole wall the fragmentation process begins.

This shock wave, which starts out at the velocity of the explosive, decreases quite rapidly once it enters the rock and in a short distance is reduced to the sonic velocity of that particular rock.

Most rock has a compressive strength that is approximately 7 times higher than its tensile strength, i. When the shockwave first encounters the borehole wall, the compressive strength of the rock is exceeded by the shockwave and the zone immediately surrounding the borehole is crushed.

The radius of this crushed zone varies with the compressive strength of the rock and the intensity of the shock wave, but seldom exceeds twice the diameter of the borehole.

However, beyond this crushed zone, the intensity is still above the tensile strength of the rock and it causes the surrounding rock mass to expand and fail in tension, resulting in radial cracking. The hot gas following the shockwave expands into the radial cracks and extends them further. This is the zone where most of the fragmentation process takes place. However, if the compressive shockwave pulse radiating outward from the hole encounters a fracture plane, discontinuity or a free face, it is reflected and becomes a tension wave with approximately the same energy as the compressive wave.

An explosive component designed to initiate less sensitive bulk explosives using an inserted detonator. Explosives delivered from a truck or tank, distinct from packaged explosives that are delivered in a box or bag. The distance between rows of blastholes parallel to the major free face or the amount of rock directly in front of a blasthole at the time of initiation.

A blasting technique that aims to maximise material movement. Casting is generally used in coal mining to minimise the amount of mechanical excavation required to expose a coal seam. The density of a substance is its mass per unit volume, usually expressed as kilograms per cubic metre or grams per cubic centimetre. Generally a higher density explosive provides more energy per unit of space. Commercial explosives have a volume between 0. The density range of the most common mining explosives is 0.

A device containing a small amount of explosive, a signal transmitter and in some cases a timing mechanism, usually enclosed in a cylindrical metal shell. It is used to initiate less sensitive or secondary explosives. Modern blasting relies on detonators for the safe and precise control of explosive energy release to achieve desired blast outcomes.

Electronic detonators differ from electric and non-electric delay systems in that the delay time is controlled by a programmed integrated circuit resulting in a high level of safety and very precise timing. A detonator that relies on a pyrotechnic signal for initiation.

Overcomes the risk associated with stray currents however does not offer the accuracy of an electronic detonator. A cord of plastic and fibre containing high explosive powder. Detonating cord may be used as an initiator or explosive charge, as is classified by the weight of explosive per metre.

A large excavation machine used mainly in surface coal mining to remove overburden layers of waste rock and soil covering a coal seam.

The machine drags a large steel bucket through waste material using cables. The act or process of creating holes in rock mass for later filling with explosive and blasting. The combined cycle of drilling and blasting, often classified as a discrete process and cost centre in most mines. The amount of energy a user can expect to have available to do effective work. It is calculated as the total energy released by explosive gases as they expand and do useful work from initial detonation pressure to a cut-off pressure of MPa 1, atmospheres.

An emulsion is a physical mixture of two immiscible liquids often water and oil formed by shearing discrete droplets of one liquid phase into a continuous phase of the other liquid. Emulsion explosives typically comprise an ammonium nitrate solution in a continuous oil phase. The undesirable products of explosive detonation including oxides of nitrogen, carbon monoxide and gases other than carbon dioxide, water and nitrogen.

The relative proportion of explosive energy available as high-pressure gas for lifting, breaking and moving rock. The process of reducing rock to finer particles for further processing, usually after crushing and prior to mineral extraction or concentration. The unexcavated face of exposed overburden and coal in a surface mine or in a face or bank on the uphill side of a contour mine excavation. Commonly called IS.

Detonators, detonating cord, primers, boosters, surface delays, lead in lines and other components used for detonating the main charges at different times. The total charge mass of explosives firing at one instant during a blast, a key measure in managing blasting vibration. May refer to a rotating machine used for reducing the size of ore particles, or more generally to the whole crushing and grinding plant. A truck with storage tanks and a processing unit designed to transport raw ingredients, manufacture bulk explosives and deliver bulk explosives into blastholes.

Factory sensitised explosive wrapped in plastic or paper and made in a range of sizes. As distinct from Bulk Explosives which are delivered directly into the blasthole from a tank or hopper.

A special blasting technique to achieve a profile closer to design than normal production blasting would. A term typically used in coal mining to refer to a separate process of overburden removal, prior to the main pass of the dragline or stripping fleet. The type of blasting most commonly used in a mine, as distinct from development, trim, presplit, ramp or other special blasts. The quantity of explosives per unit volume or unit mass of rock.

Typically measured in kilograms per bank cubic metre or kilograms per tonne of rock. Pre-splitting involves firing decoupled explosive charges simultaneously in closely spaced holes drilled along the line of excavation. The combination of a detonator and booster commonly used for the reliable initiation of a less sensitive bulk charge. A measure of the energy of an explosive, per unit volume, relative to ANFO 0.

A drill and blast service where the contractor is paid for blasted rock, and takes risks associated with drilling, geology, blast design and loading. A blasting service where the drill and blast contractor provides broken rock to an agreed size specification. A type of mill in which the larger rocks in the mill feed act as grinding media along with conventional steel ball grinding media. A primary opening in an underground mine used for ventilation or hoisting of personnel and materials.

It connects to the surface. The length of time an explosive can remain in the ground after charging and still detonate reliably. The distance between adjacent blastholes in a row, measured along the row. Spacing is nearly always larger than the burden. Scholars have used numerical calculation methods to find that the spatial stress distribution is uniform when spacing parameters are between 1. The analysis of the changes in blasting conditions and the rock breaking mechanism caused by the change of spacing parameter indicates that it can be as high as 3 to 8.

The reasonable spacing parameter for loosening blasting is from 1. Li et al. Research on loosening blasting under homogeneous rock mass conditions with large spacing parameter and the influence of joints and fissures on blasting has produced many results [ 11 — 14 ]. However, the study of large spacing parameters for loosening blasting is limited in the case of steps and large resistance lines.

The increase in the resistance line of the bench may produce large blocks, which subsequently affect the shovel loading. The increase in the charge of combined blasting will increase the mining cost and cause other unfavorable factors, such as the impact of blasting vibration, the increase of the large blocks rate, and the increase of the distance of flying stones.

Therefore, the loosening blasting of a high bench with large spacing parameter must analyze the action mechanism of cylindrical charge and the dynamic response of rocks.

The stress state of the rock medium at different resistance lines can reasonably control the size of blasting vibration and the rate of large blocks to achieve refined blasting. Raina et al. Singh et al. Zhong et al. Iwano et al. The optimum delay interval determined accurately from the superposition method was nearly equal to the one simply estimated from the method with the autocorrelation coefficient or frequency analysis of the vibration waveform in single-shot blasting [ 18 ].

Azizabadi et al. The simulated production blast seismograms were then adopted as input to predict the time histories of particle velocity in the blast vibrations on the mine wall by using the universal distinct element code. The simulated time histories of particle velocity were consistent with the measured data [ 19 ]. Navarro Torres et al.

They had knowledge of only the maximum explosive charge per delay and the distance to the blasting point. The Brazilian and international admissibility standards of blasting-induced vibration, the minimum distance between the mine and the community, and the constants obtained from the regression were used to establish the maximum explosive charge per delay for an acceptable ground vibration level that would not cause structural damage and human discomfort [ 20 ].

For the cylindrical charge, many scholars combined dynamic caustics, super dynamic strain testing, and numerical analysis methods to study the explosion stress and strain field of the cylindrical charge and the evolution law of the local stress field at the tip of the explosion crack [ 21 — 24 ]. Some scholars have also conducted intensive research on the different charge structures of columnar drug packs.

Through different positions and proportions of air deck, the action time in the cylindrical charge hole is extended to improve the utilization rate of explosives and reduce the blasting vibration [ 25 — 29 ]. At present, five technical problems must be solved for the expansion of the m-high bench in Barun open-pit mine. Second, limited by the slope of the bench, the height of the bench increases, and the resistance line of the front row is doubled. Effectively breaking and moving the rock at the bottom of the hole are greatly challenging.

Third, if the high-bench deep hole adopts a continuous charge structure, then the unit consumption of explosives under the same hole layout condition is higher than that of ordinary bench blasting, and the cost will increase. Fourth, the increase of the height and charge of the bench will inevitably lead to an increase of blasting vibration in the middle and far areas.

Fifth, the current dynamic response of the rock medium under the blasting load of the spherical or cylindrical charge will produce huge errors in the design of loosening blasting with a high bench and a large spacing parameter. In this study, the analysis of the physical mechanism of the stress wave attenuation in the rock indicates that the cylindrical charge is equivalent to several spherical charges. Meanwhile, the accuracy of the correction equation is verified.

The parameters of the high-bench blasting with good effect and low cost are determined. Finally, a field test is conducted to analyze the blasting effect. When the charge blast hole is detonated, the explosive will explode to produce high-pressure gas, impacting the wall and propagating a strong pressure wave outward into the rock medium [ 30 ].

According to the degree of damage to the surrounding rocks, three zones are formed on the rocks: the cavity, broken, and elastic zones. The elastic zone is divided into the crack and vibration zones as shown in Figure 1. Therefore, the blasting seismic wave is the propagation of the wave filtered through the broken and radial crack zones.

The cavity wall propagates under the action of the continuous expansion and contraction of the explosive gas. This process involves the interaction between the high-pressure expansion of explosive detonation products and the rock mass, the constitutive characteristics of the rock mass state of the fracture zone and the fracture zone, the size of the failure zone, and the stress time history at the interface of the failure and elastic vibration zones.

The study of this issue is the most basic and important in the study of blasting seismic wave effects. The known characteristics of the stress field of the spherical charge indicate that the law of stress attenuation is proportional to the explosive quantity and inversely proportional to the distance [ 31 ].

The energy density E of the spherical charge decays according to the cubic relationship of the expansion path R. The local field characteristic theorem of waves points out that the reflection or transmission of the incident wavefront with arbitrary shapes at any point on the curved interface is the same as that of plane waves [ 32 , 33 ].

Therefore, the transmission and reflection problems of arbitrary incident wavefront on the curved interface can be simplified as plane wave problems. The calculation method for the initial pressure of the wall of the borehole with a coupled charge is generally in accordance with the following equation: where is the explosive density, is the explosive velocity, is the explosive wave impedance, and k is the adiabatic index, which is the slope of the pressure and volume curve when the entropy value is constant, and its value is related to explosive density and explosive heat.

Chen et al. Some scholars provided a double exponential function describing the stress wave attenuation with time excited by the spherical charge [ 35 — 37 ]: where is the angular frequency, c is the propagational velocity of the longitudinal wave, and is the radius of the cavity. From the second-order partial derivative of the displacement potential function, the particle strain potential function is as follows:. The symbols are listed in Table 1. When the conditions are consistent, according to the quasi-static model of the spherical charge, Starfield approximates that the cylindrical charge is composed of multiple spherical charge stacks.

The diameter of the spherical charge should be as near as possible or equal to the diameter of the cylindrical, as shown in Figure 2. Each spherical charge has a stress effect on a certain point in the rock medium during the entire time of the positive pressure.

Assuming that the stress wave of the spherical charge reaches the specified point when the stress peak occurs, the decay time difference can be obtained: where i , j , and k are the spherical number in various cylindrical charge, is the distance from the spherical charge to the detonation point, is the starting time from the detonation point, is the detonation delay time of the cylindrical charge, and D is the explosive velocity.

According to the stress attenuation in the medium after spherical charge blasting, the radial stress at any point is calculated. The transmitted shock waves in the rock continue to propagate outward and finally become stress waves. For the force state of the element at any point in the rock as a plane strain problem, the tangential stress at any point in the rock can be obtained: where b is the coefficient of lateral, and are the radial and tangential stresses in the rock, respectively, and is the normal surface stress formed by and.

The stress tensor at any point in the rock is usually described by six independent stress components or three principle stresses acting on mutually perpendicular planes. The magnitude and direction of the stress tensor component are different for different coordinate systems, but the stress tensor and stress deflection invariants at this point will not change with the coordinate system.

Therefore, the invariants of stress and deviatoric stress tensor play an important role in strength theory.

For plastic media, the deformation state in the deformation zone must be studied, that is, the initial yield and plastic states during the deformation process when a point is in the elastic state.

Usually, the stress tensor is divided into two parts: one part is the spherical stress tensor or the hydrostatic stress tensor, and the other part is the deviatoric stress tensor. Therefore, when the stresses are equal in all directions, it is equivalent to hydrostatic pressure and does not produce plastic deformation.

Therefore, separating the same stress in all directions from the stress tensor is convenient for studying plastic deformation: where is the Kronecker symbol, is the stress sphere tensor, which represents the equal normal stress in three directions, is the stress deflection tensor, and , , and represent the first, second, and third invariants of the stress deviator, respectively.

When the x , y , and z axis directions coincide with the main axis,. For any point in space, the size of the deviatoric stress tensor part vector NP can be represented by r , and R is the size of the deviatoric stress tensor length when yielding occurs as shown in Figure 3. In the crushing area, ; in the fracture area, ; is the dynamic compressive strength of the rock; is the dynamic tensile strength of the rock.

Equations 9 — 11 can be used to obtain the stress of a point in the medium in different directions as shown in Figure 4. By substituting it into formula 14 , the effective stress at any point can be obtained as shown in Figure 5 , and then, the effective stress attenuation with distance can be obtained as shown in Figure 6.

The horizontal loosening blasting project in Barun open-pit mine was selected as the test area. The model structure is shown in Figure 7. The front and back of the bench model are defined as reflective boundaries, the slope and ground surfaces are defined as free boundaries, and the other surfaces in contact with air are defined as nonreflective boundaries.

The multimaterial ALE algorithm is used on the results of explosives and air, the Lagrange algorithm is used on the rocks and the stemming, and the fluid-solid coupling algorithm is used to reflect the stress transfer between explosives, air, and rocks.

Many methods can accurately describe the pressure change process during charge detonation in numerical simulation. The basic principle is to describe the dynamic expansion of the entire detonation chamber by combining the detonation research results of explosives with the state equation of detonation gas.

At any moment, the explosive pressure on the surrounding rock is as follows: where P is the explosion pressure, F is the chemical energy release rate of the explosive, V is the explosive detonation velocity, and are the initiation times of the current time and inside the explosive, respectively, is the maximum cross-sectional area of the explosive unit, and is the unit volume of explosive.

The parameters are shown in Table 2. The density of air is 1. The equation is expressed as follows: where — are constants, is the volume ratio, and E is the ratio of internal energy to initial volume. The Eulerian algorithm is used for the explosive, air, and blockage material models. The Lagrange algorithm is applied to the rock model. If the fluid-structure interaction algorithm is applied, no element distortion will occur. Given this advantage, the algorithm has been widely used in engineering numerical simulation with large deformation and high strain rate.

Hence, the multimaterial fluid-structure interaction algorithm can be applied to deal with the interaction process of detonation products and the surrounding rock media. The maximum unit side length in the divided model mesh is 0. The boundary of the fissure circle formed after the cylindrical charge is detonated is determined by the dynamic tensile strength of the rock. Therefore, if the effective stress peak value of each element in the model reaches or exceeds the dynamic tensile strength of this dolomite, then the rock represented by this element will be damaged.

Otherwise, the rock will not be damaged to form a fractured ring. The center planes of the two holes on the bench slope are sequentially selected from the top to the bottom, and the effective stress-time diagram is drawn. Furthermore, the monitoring points are uniformly selected at the resistance line at the bottom of the bench slope, and the effective stress-time diagram is drawn.

The middle point of the front row of holes and the position of the rear row of holes are selected as the cross-section, and the maximum effective stress is analyzed.

The effective stress of the rock mass can reflect rock fragmentation.