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Radial crack formation mechanism.

Radial crack formation mechanism.

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Article
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A common technique in hard rock tunneling, and underground excavation in general, is drilling and blasting. This method of excavation assumes that damage will be done to the surrounding rock mass depending on its quality. Herein is a proposal for how to estimate blast-damaged zone extent and shape, and how to quantify rock mass properties in this z...

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Context 1
... of an explosive charge in rock results in dynamic loading of the walls of the borehole and generation of a pressure wave that transmits energy through the surrounding medium. The pressure wave extends from borehole walls circularly around the borehole (Figure 1 Once the closed circular ring zone of rock mass is subjected to tension with a lateral strain: ...
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... define poor blasting as blast- ing where contour blastholes are drilled with a smaller span between them and charged with the same amount of explo- sive as all other blastholes. If the contour blastholes, in the blasting pattern used to create tunnel shape shown in Figure 10, are charged the same as all other blast- holes, we have a typical example of poor blasting. To compare these two methods for quantification of blast-induced dam- age in the rock mass, two FEM models were set up under the same loading and geometry conditions. ...
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... second model's analyzed damaged zone was as described in section 4. In Table 4, the rock mass parameters used in these models are shown. In Figure 10, the FEM models used for analyses are shown. The support system is the same as used in the examples of section 4. Figure 11 presents the support capac- ity plots for concrete. ...
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... Figure 10, the FEM models used for analyses are shown. The support system is the same as used in the examples of section 4. Figure 11 presents the support capac- ity plots for concrete. Figure 12 presents the maximum axial forces along the bolts for the two models. ...
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... support system is the same as used in the examples of section 4. Figure 11 presents the support capac- ity plots for concrete. Figure 12 presents the maximum axial forces along the bolts for the two models. From these plots, it can be seen that the support loading intensity is similar in both cases. ...
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... these plots, it can be seen that the support loading intensity is similar in both cases. Table 5 Maximum support loading Figure 11 Support capacity plots - a) model where blast-damaged zone is quantified using D=0.8 b) where blast-damaged zone is quantified using method proposed in this paper ...
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... pressure 0.5 GPa using equation (15) radius of cracking zone r 4 equals 0.68 m (~0.7 m) instead of 2.16 m (P h =1.6 GPa) as shown in Table 1. Figure 13 illustrates how thickness of blastholes burden impacts damaged zone extent. It has to be mentioned that one should take care about the explosive charge in blastholes that are initiated before the contour blastholes. ...

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Citations

... In blasting operation, the explosion pressure imparts dynamic loading to the surrounding medium of the blasthole. This dynamic loading causes blasthole walls to crack up and crack density decreases significantly with distance [34]. Beyond the radial cracking length, energy is dissipated in the form of stress waves. ...
... The pressure imparted by the explosive to the borehole wall after detonation is termed as blasthole pressure [51]. It is computed using Equation 5 as follows [25]: An empirical equation developed for the prediction of radial crack length using peak particle acceleration and blasthole pressure was used in this work [34]. ...
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Expansion of seaports often necessitates demolition of old berths near newly constructed berths. The 'Underwater drilling and blasting' technique is generally preferred for demolition due to higher economy and least dismantling time. The structural vibration in terms of Peak Particle Velocity (PPV) was to be limited below 75 mm/s for the structures located in the proximity as well as 508 mm/s for the connected concrete berth for preventing distress if any. Based on the scaling law established, a Hybrid Controlled Blasting (HCB) technique by redesigning the delays and charge quantities was established. The blast-induced radial crack was also estimated from stress theory to fix the distance between the pre-split hole and line drilling row as 1.5 m for an estimated charge per hole of 2.5 kg. One pre-split hole and two rows of 3 empty holes were drilled in a staggered pattern and blasted to detach the structure safely. The HCB technique helped in successfully screening the structural wave propagation and radial crack beyond the line-drilling row. The vibration progressively reduced from a predicted value of 87.59 mm/s to an actual value of 67.1 mm/s at the monitoring station. The structural strain was also controlled from 1925.4 μmm/mm to less than crack initiation threshold of 1143 μmm/mm at the nearest distance on the adjacent berth. The post-blast survey conducted confirmed that no crack was induced to adjacent berths proving the utility of the technique developed.
... де P1 -тиск продуктів вибуху на стінки зарядної порожнини з урахування діаметру заряду ВР, згідно з [11] з достатньою точністю можна визначити як ...
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Modeling of rock mass destruction by explosion allowed to obtain mathematical models of the formation of crushing zones, intensive grinding and crack formation, which are formed around the charging cavity in the rock mass with taking into account the diameter of the charging cavity and the diameter of the explosive charge, detonation compaction of rocks under the action of rock pressure. According to the obtained mathematical models, the radii of the crushing zones, intensive grinding and crack formation during blasting in the charging cavity of the cartridge emulsion explosive Ukrainit-P-SA and bulk emulsion explosive Ukrainit-PP-2 were calculated. This allowed us to establish that the diameter of the explosive charge significantly affects the pressure of the explosion products in the charging cavity. It is established that during the charge of bulk emulsion explosive Ukrainit-PP-2 is detonated, the radii of the destruction of the rock mass around the charging cavity are increased by 1.5 – 2.0 times in comparison with the cartridge emulsion explosive Ukrainit-P-SA.
... Далі проводили аналіз отриманих результатів розрахунку величини радіусу зони інтенсивного подрібнення за методикою Torbica S., Lapčević V. [14,15], які порівнювали з результатами чисельного рішення математичної моделі за запропонованою методикою для умов монолітного нетріщинуватого масиву отриманих за формулою (43). Розбіжність результатів за цими методиками не перевищує 9%, що вказує на високу достовірність отриманих результатів та коректності чисельного рішення математичної моделі зони інтенсивного подрібнення. ...
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Mathematical models of the formation of breaking zones, intensive grinding and cracking, which are formed around the charging cavity in the rock massif with taking into account the action of rock pressure and energy characteristics of the explosives were created based on the results of modeling of the action of the explosion in a solid medium. Numerical solution of mathematical models allowed to establish the power dependences of the formation of these zones, which occur in monolithic non-fractured and fractured massifs under their explosive loading, depending on the physical-and-mechanical properties of rocks, energy characteristics of explosives and rock pressure. Comparison of the results of numerical modeling of the radiuses of these zones with previously identified patterns allowed to establish the discrepancy of the results with already well-known methods, which does not exceed for the zone of compression and cracking up to 1%, and intensive grinding up to 9%. Application of the obtained results of modeling the radiuses of the breaking zones, intensive grinding and cracking, which are formed in the rock massif around the charging cavity, allows calculating the line of least resistance for blast holes and boreholes during mining.
... When BIDZ is included in the analysis, the dead weight of this broken zone exerts higher pressures to the support system at the crown (roof) of the tunnel which leads to safety factor decrease (e.g. Torbica andLapčević 2015, Hedayat et al. 2018). This needs to be considered in the elasto-plastic analysis of the tunnel. ...
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The rock mass properties are typically influenced by the excavation technique and the changes in the state of stress due to the rock excavation. The amount and extent of damage introduced in the rock mass depends on the excavation technique and practice quality. The influence of blasting in the rock mass near the tunnel periphery is far more significant due to the energy of waves and redistribution of stresses and the severity of the damage diminishes as the radial distance from the tunnel opening increases. Therefore, it is important to consider the effect of the damaged zone when analysing the stresses and deformations around a tunnel. This study aimed at providing a new numerical solution for the determination of the ground response (reaction) curve with the consideration of the non-uniform damage zone around the tunnel periphery. A deep circular tunnel subjected to hydrostatic stress condition and excavated in rock materials obeying the Hoek-Brown failure criterion is considered. A solution for the determination of stresses, strains, and deformations around the circular deep tunnel is presented in order to correctly assess the attenuation of damaged rock as the distance from the tunnel perimeter increases considering the loads applied to the supporting structure.
... Author, reference Formula Conventional signs Mosynets V.M., Horbachova N.P. [22], [34], [ roblasthole radius, cm; ρeexplosive density, g/cm 3 ; eANFOforce (strength) of an explosive relative to ANFO; ρANFO -ANFO density equal to 0.85 g/cm 3 ; γrock density, g/cm 3 Torbica S., Lapčević V. [47], [48] ( )( ) ( ) , m nnumber of radial fractures for the fracturing zone n = 4 pcs. ...
... The modern theory of the rocks destruction by blasting, presented by Serbian scientists S. Torbica and V. Lapče-vić [47], [48] makes it possible to assess the length and density of radial fractures caused by the initiation of an explosive charge. Based on this theory, a method is proposed for determining the size of the explosion zone and quantifying the rock mass properties. ...
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Purpose. 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 pro-perties 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 char-ging 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.
... Importance of the proper cut design are widely reported and explained in literature (AyalaCarcedo, 2017;Zhang, 2016;Xu, Li, Liu, & Zhang, 2019). Damage of surrounding rock mass due to improper blasting is one of the problems that needs to be taken care of since it may provide instabilities (Torbica & Lapčević, 2016;Torbica & Lapčević, 2015;Torbica & Lapčević, 2018) and higher quantity of materials to be handled. Previous works on blasting optimization in Lece mine were considering ring blasts and is available in (Duranović, et al., 2018). ...
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... Sharifzadeh and Pal [12] attempted to quantify the blast damage factor by deducing a relationship between deformation modulus and intact rock modulus by taking the blasting effect into consideration. Torbica and Lapcevic [13] quantified the blast damage by reducing the geological strength index (GSI) by 10 units in the damaged rock zone. It was concluded that the results of the reduced-GSI method were equivalent to that of the D factor, showing that reduced GSI can be used as an alternative for determining the properties of the degraded rock mass. ...
... Mitelman and Elmo [16] developed a hybrid element discrete modeling approach to study the induced damage in tunnels. Phase2 was used to demonstrate the blast effect on the tunnels where the degraded rock properties were used for only the specified thickness of the blast zone [13]. In these studies, the periphery of the tunnels was simulated by reducing the intact rock properties of the blast-effected zone. ...
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Pillar stability is an important factor for safe working and from an economic standpoint in underground mines. This paper discusses the effect of blast damage on the strength of hard rock pillars using numerical models through a parametric study. The results indicate that blast damage has a significant impact on the strength of pillars with larger width-to-height (W/H) ratios. The blast damage causes softening of the rock at the pillar boundaries leading to the yielding of the pillars in brittle fashion beyond the blast damage zones. The models show that the decrease in pillar strength as a consequence of blasting is inversely correlated with increasing pillar height at a constant W/H ratio. Inclined pillars are less susceptible to blast damage, and the damage on the inclined sides has a greater impact on pillar strength than on the normal sides. A methodology to analyze the blast damage on hard rock pillars using FLAC3D is presented herein.
... Many scholars have used continuum (e.g. Ma and An 2008, Wei et al 2009, Banadaki 2010, Banadaki and Mohanty 2012, Torbica and Lapčević 2015 and discontinuum (e.g. Park and Jeon 2005, Yoon and Jeon 2009, Ning et al 2011, Onederra et al 2012, Aliabadian et al 2014, Fakhimi and Lanari 2014 numerical modeling tools to simulate the blasting process. In these studies rock mass damage has been defined based on the observation of the plastic deformation zones induced by the blast and/or by measuring particle peak velocity (PPV) results (Wei and Zhao 2008). ...
Article
In order to study the damage induced by rock blasting, a numerical simulation method based on the Johnson-Holmquist II (JH-2) damage model combined with the arbitrary Lagrangian-Eulerian (ALE) method is proposed. The process of dynamic breakage and damage evolution of Barre granite is reproduced using explicit hydrocode, ANSYS/LS-DYNA, based on the prototype experiments in the laboratory. The results show that both the crack patterns and measured pressures are in agreement with the results from the lab-scale experiments. The attenuation curves of the pressure and particle peak velocity (PPV) along the radial direction are respectively determined, and the corresponding theoretical formulas are summarized together with the most suitable attenuation exponent α. In addition, comparisons of blasting tests separately carried out using the discrete element method-smoothed particle hydrodynamics hybrid method and the ALE/JH-2 method demonstrate similar crack patterns formed both in intact rock disks and jointed rock disks. In the jointed rock disk, the pressure sharply declines when crossing the joint surface, while the PPV close to the joint increases before going across the joint surface, representing the 'weak transmission - strong reflection' effect of the joint surface. Different yield stresses of joint properties are further studied, which indicate that joints with a lower magnitude of yield stress can prevent more transmissions of waves crossing the joint surface. In future studies, the ALE method combined with the JH-2 damage model can be applied to larger-scale rock engineering problems to optimize the blasting design.
... Kanchibolta et al. (1999) Fig. 1 Fracture process of explosive blasting (Whittaker et al. 1992) these works tried to provide theoretical solution for the blasting-induced damaged zone, simplification and assumption cannot be avoided due to the complexity involved with the fragmentation process. And these models are only considered for estimating the extent of the blastdamaged zone (Torbica and Lapcevic 2015). In fact, there are several studies to evaluate fragmentation zone by introducing gas-driven fractures in blasting (e.g., Nilson et al. 1985;Paine and Please 1994). ...
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This paper presents a simple method to evaluate the two-dimensional fragmentation zone induced by gas pressure during blasting in rock. The fragmentation zone is characterized by analyzing crack propagation from the blasthole. To do this, a model of the blasthole with a number of radial cracks of equal length in an infinite elastic plane is considered. In this model, the crack propagation is simulated by using two conditions only, the crack propagation criterion and the mass conservation of the gas. As a result, the stress intensity factor of the crack decreases as crack propagates from the blasthole so that the crack length is determined. In addition, gas pressure inside blasthole also continues to decrease during crack propagation. To validate suggested analytical solution, discrete element method is used by comparing length of propagated crack due to blasting.
... In addition, the number (n) of radial tensile cracks formed at a distance cn r will be: In Figure 2, the schematic illustration of tension crack length and density around blast hole is shown. Practical application of this theory was demonstrated for the estimation of blasted rock fragmentation [13] and for the blast damage zone extent estimation [14]. ...
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Achieving optimal fragmentation of the blasted rock is common task for mining engineers. During the years many models for fragmentation prediction were developed and are mostly based on empirical relations. While there are theoretical expansions of the empirical models, one could note the lack of the purely theoretical models based on the rock breakage theory. Herein, validation of such model is presented. Model considers only the fragmenting of the cylindrical monolith rock specimens and compares the results with the laboratory tests that were carried out in same manner. Model provides results through the definition of the fragment shape and size and then geometrical fragmenting of the whole specimen. Comparison of the model and laboratory results shows high level of agreement between sieving curves and also confirm the right constitution of the rock blasting theory that this model is based on.