انفجار

In the blast phenomenon, the explosives release a lot of energy, which causes damage and fractures the rock mass. One of the influencing parameters in the blasting results is the way the blast hole is charged. Power Deck blasting has been introduced as a blasting method to reduce or eliminate sub-drilling, optimize crushing, and reduce undesirable results. The purpose of this research is to investigate the impact of the Power Deck blasting method on the borehole pressure and damage to the rock mass compared to the conventional method. In this regard, the numerical simulation of a single blast hole was carried out using conventional and Power Deck methods by using LS-DYNA software. The results showed that in the Power Deck method, in the area of the air deck, the initial pressure of the hole is reduced compared to conventional blasting, and secondary pressures are produced, which leads to a reduction in the expansion of the hole along the air deck by 45% and increases the destruction in multi-stage. On the other hand, the generation of secondary pressures in the Power Deck method causes a 30% and 48% increase in rock mass destruction in the area of the bottom of the hole compared to the conventional method. As a result, the Power Deck blasting method improves the amount of expansion and destruction by using less explosive, which indicates the optimal use of the explosive energy.

Pile movement is one of the rock blasting outcomes that, considering the type of haulage machines, has a direct effect on the efficiency of the loading process. In this study, using UDEC discrete element software, the pile movement of fragmented material caused by the blasting operation is modeled. Since UDEC is not capable of modeling the whole process of rock blasting, to accurately model the pile movement of fragmented material, the damping coefficients must be changed in a way to allow the move freely out of the split blocks after the blast, be modeled. The numerical modeling results show that implementing a negative exponential function with three (the initial, threshold, and power) eigenvalues, as the fish-function to the damping coefficient, can model the results pile movement. With the help of this damping function, three blasting blocks with one and two rows of blast holes were modeled. The results of these modeling show that the pile movement for the two rows of blast holes depends on the inter-row delay time, and for the delay times of 17 ms and 50 ms, the maximum horizontal movement of the pile was 30 m and 55 m, respectively. These values show good agreement with the values measured in an actual blast operation. The results of this study show that by changing the negative exponential function eigenvalues defined for damping, the velocity of the fragmented blocks, the displacement, and the geometry of the pile, could be modeled. This shows the capability of the discrete element method in the modeling of the results of rock blasting.

The explosion of explosives in the blast-hole can apply very high pressure to the surrounding rock media. The pressure can cause to propagate cracks and fractures and eventually fragment and destroy them. Rock blasting, like other dynamic phenomena, needs to propagate waves and dynamic stresses through the body. Therefore, the study of the propagation of waves is of great importance in understanding the subsequent effects of rock blasting. For this purpose, an analytical algorithm is used to obtain the appropriate Green functions to achieve the best description of the problem. To solve the blast-induced wave propagation problem.

Methodology and Approaches:

A two-dimensional elastodynamic Green's function has been analytically derived. Firstly, Navier's equations of motion and explosion equations have been used as governing equations. Then, using the Helmholtz theory, the Navier equations have been separated into two scleral and vector fields in terms of displacement. Explosion pressure as a body force has been added to the equations using the Poisson function. After performing the relevant calculations and solving the above equations, the corresponding Green function in terms of displacement is obtained. Moreover, a time-dependent green function is developed for the particle velocity using the basic functions and the resulting green function. After finding the appropriate Green functions, a typical problem consisting of a blast-hole in an elastic homogenous isotropic infinite rock media has been investigated and modeled. Finally, to validate, a real problem has been analytically modeled and solved using the proposed solution.

Its results have been compared with results from a finite element-discrete element numerical method and the explosion reality results. Based on the results of the comparison, there is a good agreement between the analytical, experimental, and numerical results at different distances from the blast-hole. A good match between the analytical results of this study and the experimental and numerical results of previous studies shows the validity of the proposed method and confirms the Green function obtained in this study. In general, it can be said that this method can be used to study the propagation of elastic waves in rock and rock-like materials. Also, it can be utilized from the resulting Green functions in other methods for different purposes as an input dynamic function.

Nowadays, duo to mining and construction activities' progression, the need to utilize blasting has been increasing in order to reduce time and cost. The use of blast for drilling and crushing rock, in addition to its advantages, has disadvantages, the most important of which is ground vibration. Vibration caused by the blast is an important and significant part of the blast process and controling its amount in order to reduce possible damage to the surrounding areas, is always necessary. In this paper, the field data of the blast in the second line of the Tabriz water pipeline project have been collected using three-component Blast Recorder seismographs. By modeling the process of blast in ANSYS-Autodyn finite element software, the behavior of the blast zone environment is simulated. The average of numerical modeling errors compared to field surveys is estimated at about 20%. According to the numerical modeling, the most critical state of velocity entering the pipeline is less than the allowable blast standards near the pipeline, and the maximum stress, strain, and displacement in the boundary of pipe and soil are equal to 17.24 MPa, 135 μmm /mm, and 0.18 mm, respectively.

Prediction of maximum safe charge per delay (Q , kg) by Distance (D) from blasting point and adaptive Peak Particle Velocity (PPV) is a critical key for successful blasting. Safe charge per delay is calculated by using PPV estimators indirectly or Q estimator directly. This paper presents the results of ground vibration measurement induced by bench blasting in Sungun copper mine. The scope of this study is to evaluate the capability of different methods in order to predict maximum safe charge per delay. Conventional empirical models and two type of new non-linear dirict estimator models are prsented. An application of Imperialist Competitive Algorithm (ICA) has used to determine the Q estimator coefficients in Sungun bench blasting. A comparison between two ways of investigations including conventional empirical equations and ICA are done. It has been shown that the applicability of ICA-based equations is more promising than any selected traditional empirical equations.

One of the major problems related to blasting operations in open-pit mines is the formation of cracks on the benches behind the last row of blast holes or back breakes. Power Deck blasting has been introduced as a new and alternative method for conventional blasting, which improves blasting results by explosive energy utilization enhancement. In this technique, there is an air deck at the end of the blasting hole which decreases or eliminates sub-drilling. Power Deck blasting reduces charge per delay in the same conditions as conventional blasting and charge per delay is one of the most effective parameters of back break. In this study, back break caused by conventional and Power Deck blasting was evaluated in the Mishdovan iron ore mine. Back break in Power Deck blasting was reduced by 16.4% and 55% in iron ore and stone waste respectively as compared to back break in conventional blasting. Power Deck blasting could therefore be effectively used as a controlled blasting technique to obtain stable faces. Also after loading and hauling the fragment size, it was found that both methods have no significant differences in flat floors. Eventually, the Power Deck method reduced powder factor and specific drilling by 28.5% and 9%, respectively. In addition, holes productivity improved by 9% in Power Deck blasting compared to conventional blasting.

In this paper, the effect of time delay interval on blast-induced weakness has been studied. For this purpose, three similar concrete blocks with dimensions of 50 ×30×14 cm have been constructed and a number of experiments have been designed and performed on these blocks. In each block, three rows with three blastholes in each row have been drilled. The diameter of the blastholes is 6 mm and pacing and burden were designed 75 and 50 mm, respectively, giving an S/B ratio of 1.5. Twelve points were arranged on the blocks in four lines and three rows to measure ultrasonic wave velocity before and after delay blasting. Blocks were blasted by detonating cord of 12 g/m in three different delay time intervals between rows including 25, 50, and 75 millisecond. Weakness index was defined by incorporating difference of ultrasonic wave velocity in intact and blasted blocks. The results were analysed and discussed for different measuring directions and contour plot of weakness in blocks was plotted. This study concludes that increasing of time delay interval has different effect on the magnitude and distribution of weakness.

Producing more fragmented rock by blasting requires increased costs in drilling and blasting operations. On the other hand, it leads to a reduction of loading, haulage operation and no need for secondary blasting. In this study, the effective parameters in machinary efficiency of Sarcheshmeh Copper Mine was explored. For this purpose, the ratio parameter of length to width of the blast block (RLW) and the Loading parameters including Operation(O1), Failure(F1), Ready (R1), Movement of loading machine (M1), were introduced, measured and used. The blasing block's ratio of length to width (RLW) parameter is presented in most of the proposed models. This parameter has been effective in efficiency of loading machinary. The high correlation coefficient of a loading cycle of machine’s bucket (C1) with the independent variables shows that this variable is more affected by the fragmentaion and the dimensions of blasted blocks. The best and the worst of a loading cycle of machine’s bucket (C1) are equal to 14.38 and 51.15 seconds in Sarcheshmeh Copper minefor which (D50) corresponds to 3.02 and 10.39, cm respectively and (D80) equals to 6.69 and 24.49 cm, respectively. The Correlation coefficient of 0.8 for specific loading (S1) indicates the high influence of fragmentation caused by blasting operations on specific loading (S1).

Assessment and prediction of rock fragmentation by drilling and blasting operations, the most basic and most critical parameters affecting the economy of mine is considered. Choghart mine had one of the largest Iran iron ore mine that annual eight million tons of iron ore is extracted from it. In the mine mining operations, including drilling, blasting, loading, transportation and processing is done on a daily basis. Distribution of aggregation from blasting operations and resulting machinery production, mining costs may be reduced. There are several methods to determine the blasting fragmentation and currently, the use of image processing systems is appropriate and effective method for evaluating of blasting fragmentation. In this study, sieve analyzes of three patterns of explosive in Choghart mine and fragmentation curve obtained by the image processing method is compared and then this method for more accurate predictions in mine by factors of α and β is correct. The correction factors value respectively is 0.81108 and 0.82087.

Backbreak and subject of reduction in the bench dip respect to the blasthole dip have the important role on the stability and design of remained bench wall after blasting. Effects of parameters of blastholes and charging due to surface mines including: blasthole diameter, blastholes spacing, burden, stemming, blasthole length, blasthole dip, under drilling, charge quantity in each delay and powder factor on the backbreak distance and varying the reduction of bench dip angle (β) respect to the blastholes dip angle (α) have been investigated by various blasting operations in Eyvughly gypsum mine, Rashakan limestone mine, Sungun copper mine and Gholghohar iron mine in this research. Each parameter of backbreak distance (Lb) and varying the reduction of bench dip respect to the blastholes dip increases with an increase of blasthole diameter, blastholes spacing, burden, stemming and blasthole length. The parameters of Lb and () show better correlations with the blasthole diameter and blastholes spacing (S). The parameters of Lb and dont show correlation with the three parameters of under drilling (U), charge quantity in each delay and powder factor. The multivariable relationships between parameters of backbreak distance (Lb) and varying the reduction of bench dip respect to the blastholes dip () with the combination of five blasthole parameters including: diameter, blastholes spacing (S), burden (B), stemming and blasthole length were obtained by statistic analysis using SPSS program with correlation coefficient (R) of 0.948 and 0.960 respectively. The amount of backbreak distance (Lb) and varying the reduction of bench dip respect to the blastholes dip can be predicted and controlled using the obtained multivariable relationships. The parameters of blastholes have important effects on the backbreak and dips of mine benches, and proposed relationships can be useful for stability analysis and design of mine benches due to the blasting operations.