To mitigate the level of blast-induced vibrations, the time-delay experiments involved 5 delay intervals, 8 holes and 11 monitoring stations, were undertaken in a newly constructed underground mine. ...The method of instantaneous energy based on the empirical mode decomposition (EMD) was adopted to identify the actual delay times from the near-field accelerations. Then the Theil-Sen regression was adopted to analyze the vibration attenuation. Based on the drawbacks of the field experiments due to various unpredictable factors, the blast damage model was further employed to make a comprehensive understanding of the effects of delay times. The signature invoked the average waveform of multiple holes in the experimental 75 ms case, then a group of fluctuating signature waveforms were generated from the Monte Carlo scheme based on waveform comparison between the measured and the signature. Upon completion of the model verification, the number of delays was examined within four delay intervals, and 25 delays were selected to figure out the effects of delay times and delay errors. The results state that the peak particle velocity (PPV) and average frequency (AF) are insensitive to delay times irrespective of delay errors, except short delay times. The vibration dominant frequency (DF) is mainly contributed by idea delay times and delay errors, and the optimal delay interval is half of the dominant period, which is only effective to improve DFs at a target location. The commonly used pyrotechnic detonator is competent in most blasts unless structures need to be protected from their resonances.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Most mines choose the drilling and blasting method which has the characteristics of being a cheap and efficient method to fragment rock mass, but blast-induced ground vibration damages the ...surrounding rock mass and structure and is a drawback. To predict, analyze and control the blast-induced ground vibration, the random forest (RF) model, Harris hawks optimization (HHO) algorithm and Monte Carlo simulation approach were utilized. A database consisting of 137 datasets was collected at different locations around the Tonglvshan open-cast mine, China. Seven variables were selected and collected as the input variables, and peak particle velocity was chosen as the output variable. At first, an RF model and a hybrid model, namely a HHO-RF model, were developed, and the prediction results checked by 3 performance indices to show that the proposed HHO-RF model can provide higher prediction performance. Then blast-induced ground vibration was simulated by using the Monte Carlo simulation approach and the developed HHO-RF model. After analyzing, the mean peak particle velocity value was 0.98 cm/s, and the peak particle velocity value did not exceed 1.95 cm/s with a probability of 90%. The research results of this study provided a simple, accurate method and basis for predicting, evaluating blast-induced ground vibration and optimizing the blast design before blast operation.
Decoupled charge structures are widely used in contour blasting because of their lower peak value and loading rate of the borehole wall pressure (BWP), which plays an important role in the contour ...blasting effect. The filling medium and decoupling ratio are the two key factors of decoupled charge blasting, and their effects on the peak value, rise time and loading rate of BWP need to be investigated. In the present study, physical model tests of decoupled charge blasting on cement mortar blocks (400 × 400 × 200 mm) were conducted under different filling mediums and decoupling ratios, and polyvinylidene fluoride (PVDF) gauges were used to directly measure the BWP. In addition, a numerical model was developed and verified to simulate the same decoupled charge blasting tests and some other tests with additional decoupling ratios. The measured and simulated results both showed that the peak value and the loading rate decreased with increasing decoupling ratio. Compared with the theoretical formulas, the modified power function formulas provide more accurate peak values. The peak pressure, rise time and loading rate were higher in water-coupled blasting, and the ratio of the peak pressure in water-coupled blasting to that in air-coupled blasting was between 2.35 and 4.28 under decoupling ratios of 2∼5. When the peak pressure was the same, the loading rate in the water coupling blasting was always lower than that in the air coupling blasting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•An effective raise blast technique with vertically parallel and dense bunch holes.•An accurate numerical model for raise blasting under in-situ stress.•In-situ stress governs the radial cracks but ...has little effect on the crush zone.•In-situ stress can reduce PPA and frequency of the blast-induced vibration.•Short-delay blast can effectively reduce the cut blasting induced vibration.
In deep underground mining, the damage evolution and vibration response mechanisms of rock caused by cut blasting are different from those of shallow rock. It is essential to understand the mechanisms for underground engineering safety. In this study, field raise blasting with vertically parallel and dense bunch longholes was designed and performed at the Shaxi underground mine in China. The raise contour and the blasting vibration were measured in the field, and regression analyses of the peak particle acceleration (PPA) were performed. Then, a numerical model considering the effect of in situ stress was developed and calibrated to simulate raise blasting excavation. The damage contours show that the in-situ stress can reduce the radial fractures outside the raise, but has little influence on the crater. The vibration analyses indicate that the PPA and the average frequency (AF) decrease with an increasing in-situ stress. The confinement effect of in-situ stress on vibration characteristics is discussed, and blast loading relative pressure curves are presented for a demonstration. It is determined that the relative pressure peak value decreases, and the rising time and duration time increase with an increasing the in-situ stress; as a result, the blast-induced vibration is lower in amplitude and AF. In terms of the frequency, the vibration from a higher in-situ stress is more harmful to structures. A short-delay blasting model was conducted, and the results show that it can effectively reduce the structural vibration damage caused by cut blasting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Attenuation assessment of vibration induced by underground explosions is a source of concern due to its associated with damage analyses of underground facilities and ground structures. Based on the ...blast events at different levels of ore have different impacts on ground structures, to understand the attenuation rule of vertical propagation is essential for the safe design of mining blasts. In a new-built underground mine, eight seismographs were installed with different depths to monitor the blast vibrations, and 236 events included 24 events on the ground were recorded during mining production over a period of eight months. Certainly, the blasting design, propagating medium and its mechanical parameters were also carefully investigated. In the light of the collected data, various prediction equations are employed to establish a suitable relationship for describing the attenuations of peak particle velocity (PPV) and frequency. The charge weight effect on the frequency attenuation of the induced ground motion is also discussed. Moreover, the effect of surface soil overburden has also been analyzed based on a supplementary monitoring work. The results indicate that scaled distance (SD) with cube root scaling for the explosive quantity can properly perform the far-field vibration. Irrespective of how much the item of charge weight represents, its simplified form still makes the oldest equation still be widely used. The average frequency (AF) and its modified frequency equation perform well in the rock mass. The soil overburden has a low-impact on the ground motion, while the influence of charge weight per delay on ground wave frequency has diminished.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Delay blasting with relatively long-delay intervals is widely used in mining engineering since the former detonated blast-holes can produce new free surfaces for the later detonated blast-holes. With ...the application of electronic detonators, which have a minimum delay and a delay accuracy of 1 ms, a new blasting pattern using short-delay intervals is proposed in the present study in order to improve rock breaking and control blast-induced vibrations in cutting blasting with single free surface in underground mines. Theoretical analyses are firstly conducted to investigate the mechanisms of blasting crater formation and vibration reduction of short-delay blasting. Then a series of blasting crater tests with different delay intervals are performed to compare the characteristics of blasting craters and blast-induced vibrations produced by short-delay and simultaneous blastings. The results of crater sizes show that it is possible to form a common blasting crater only when the delay intervals are shorter than the formation time of a new free surface. It is also found that the short-delay blasting can effectively reduce PPV compared with the simultaneous blasting, particularly in the near-field. Spectral analysis indicates that there is less energy in the low-frequency content in short-delay blasting than simultaneous blasting. The possibility and feasibility of reducing vibration via short-delay blasting in underground mines are also discussed in this study.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
It is generally believed that stress wave superposition does occur and plays an important role in cutting blasting with a single free surface, in which explosive columns of several blast holes with ...short spacing are simultaneously initiated. However, considering the large scatter of pyrotechnic delay detonators that are used in most underground metal mines in China, the existence of stress wave superposition and the influence of this effect on rock fragmentation are questionable. In the present study, the stress wave interaction in short-delay blasting with a single free surface was studied through the use of the LS-DYNA code. Stress waves induced by two blast holes blasting with different delays were compared with the single blast hole case, and the effects of delay time, detonating location and spacing on stress wave superposition were investigated. The numerical results showed that for blast holes with a 1 m spacing, stress wave interaction only occurs when the delay time is 0 ms and does not occur for blasting with delays of more than 1 ms. An increase in the duration of a stress wave via optimizing the detonation location does not improve the stress wave interaction. For a 1 ms delay, stress wave superposition only occurs when the spacing is more than 4 m, which is a rare case in practice. The results indicated that the occurrence of stress wave superposition for blasting with a single free surface is strictly limited to conditions that would be difficult to achieve under the existing delay accuracy of detonators. Therefore, it is unrealistic to improve fragmentation via the stress wave interaction in field blasting. Furthermore, the numerical results of the stress wave interaction also show that there would be a great potential to reduce the hazardous vibrations induced by short-delay blasting by using electronic detonators with better control of delays in an order of several milliseconds.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Studies of the mechanical response behavior of slate and the establishment of corresponding damage-ontological relationships are crucial for improving safety and avoiding disasters in construction ...projects. For the study reported in this paper, we first assumed that slate is a transverse isotropic body. Next, to characterize disparities in elastic characteristics between axial and radial orientations, we introduced five distinct elastic parameters for these two directions. Specifically, these parameters were Young’s modulus
E
1
, Poisson’s coefficient
v
1
(associated with parallel bedding planes), Young’s modulus
E
2
, Poisson’s coefficient
v
2
, and shear modulus
G
2
(associated with perpendicular bedding planes). We then established a statistical damage-evolution equation for transverse isotropic slate based on a lognormal distribution, and we constructed a statistical damage-constitutive model for laminated slate under three-way stress by considering the shear–slip deformation and closure deformation of the laminated surface. Finally, we demonstrated the effectiveness of our model by comparing its output data with results obtained in triaxial compression tests on slate. We found that the differential stress–strain curves obtained from the model and the tests were in good agreement in the peak front. Average relative errors of 15.62% and 16.19% were recorded for cases of 5 Mpa and 10 Mpa of enclosing pressure, respectively. The rationality of the established transverse isotropic slate damage-constitutive relationship was therefore proved.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Cut blasting, in which new surfaces and relief space for subsequent blasting are created, is one of the most critical steps in the establishment of large-diameter long-hole (LDL) stopes. To reduce ...the damage to the chamber roof caused by stemming recoil and improve the rock breaking effect, 15 groups of small-scale model tests with minimum burdens of 3, 4, 5, 6, and 7 cm and stemming lengths of 0, 2, 4, 5, 6, and 7 cm were designed to optimize the matching relationship between the stemming length and minimum burden. First, through the model tests, values were obtained for ten evaluation indexes related to the total mass of fragments, crate size, fragment size, fragmentation energy consumption, and stemming recoil area. Then, the normal cloud combination weighting method was used to combine six subjective and objective weighting methods, and combined weights were obtained. Finally, the test schemes were optimized according to the Euclidean distance and similarity. The test results showed that the best blasting scheme involves a burden of 5 cm and a stemming length of 5 cm, followed by that involving a burden of 4 cm and a stemming length of 4 cm, and the optimal stemming length is approximately equal to the minimum burden. A field test of LDL stope cut blasting was conducted, with a stemming length of 2.2 m and a minimum burden of 2.2 m in the boreholes. The highly satisfactory field blasting effect indicates that the stemming length and minimum burden are reasonable.
Highlights
Ten indexes were obtained and normalized for each of the eight test schemes. Six weighting methods were used to obtain the respective weights, and the normal cloud combination weighting method was used to obtain more reasonable weights.
The optimal scheme was that involving a burden of 5 cm and a stemming length of 5 cm, followed by that involving a burden of 4 cm and a stemming length of 4 cm. The optimal stemming length was approximately equal to the minimum burden.
An on-site cut blasting test was conducted of the N10#S stope in the Fankou Mine. The upper part of the explosive packs exhibited a stemming length of 2.2 m, and the lower part exhibited a burden of 2.2 m. The highly favorable field blasting effect proves that the above stemming length and minimum burden are reasonable.
The high reactivity of the acetylene group enables the formation of strong chemical bonds with active sites on mineral surfaces, thereby improving the flotation performance of gold minerals. This ...study utilized density functional theory (DFT) to analyze the quantum chemical parameters of structure, Mulliken population, and the frontier orbitals of a thioester collector containing an acetylene group, PDEC (prop-2-yn-1-yl diethylcarbamodithioate). PDEC was compared with analogous thioester collectors Z-200 and Al-DECDT. The interaction mechanism of PDEC on the Au(1 1 1) surface was simulated, followed by empirical validation through adsorption experiments. The findings indicate that the S atom of PDEC in the carbon–sulfur group exhibits shorter covalent bond lengths, and has reduced carbon–sulfur double bonds and Mulliken population, resulting in enhanced electron localization. This confers greater selectivity to PDEC during its adsorption on mineral surfaces. Frontier orbital analysis shows that the electrons of the acetylene group possess a notable electron-accepting capacity, significantly influencing the frontier orbital energy of PDEC and playing a pivotal role in the bonding interaction with mineral surfaces. Both the S atom in the carbon–sulfur group and its acetylene group establish stable adsorption structures with the A(111) surface in a single coordination mode. The adsorption energy sequence is PDEC > Al-DECDT > Z-200. Partial density of states demonstrates that the S 3p orbit of the carbon–sulfur group hybridizes with the Au 5d orbit, while the C 2p orbit of the acetylene group engages in weaker back-donation bonding with the Au 5d orbit. This is corroborated by the electron density difference and post-adsorption Mulliken population analyses, revealing that the S atom of the carbon–sulfur group in PDEC donates electrons to the Au atom, forming dominant positive coordination bonds, whereas the acetylene group accepts partial electrons from the Au atom, resulting in weaker back-donation bonds. The adsorption experiments align with the DFT adsorption energy results.
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