Soil microbes are essential links between above- and below-ground ecosystems and play an important role in regulating ecological functions in the soil. Dynamic interactions within the soil-microbial ...community in a cereal-legume intercropping ecosystem influence the composition and structure of N-cycling microbial groups (e.g. nitrogen-fixing bacteria). However, these effects have not been extensively studied in some intercropping patterns or in response to varying nitrogen fertilization levels. In the present study, we evaluated the effects of reduced and conventional nitrogen application in a sweet maize (
Zea may
L.)/soybean (
Glycine max
L.) strip intercropping system under three cropping patterns over a 3-year time period. High-throughput sequencing and quantitative PCR techniques were used to investigate changes to both the microbial community structure and the expression of key nitrogen-cycling genes in the rhizosphere. Our results indicate that reduced nitrogen application affected the microbial community structure in the rhizosphere, but microbial diversity in the sweet maize rhizosphere was relatively stable. Both the abundance and activity of functional marker genes for microbial nitrogen fixation (
nifH
), nitrification (
amoA
), denitrification (
nirS
,
nirK
,
nosZ
), and decomposition (
chiA
) increased significantly from 2013 to 2016. Taken together, these data demonstrate that the quantified shifts in the soil microbial community and the observed increases in the expression of key functional genes involved in N-cycling were the result of reduced nitrogen application in this strip intercropping system. This study, therefore, provides essential insight into the potential relationships between functional nitrogen-cycling genes and mitigation of nitrogen-loss and N
2
O emissions in a cereal-legume strip intercropping system.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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
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
The stability of cemented paste backfill (CPB) is threatened by dynamic disturbance, but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose. ...Therefore, a split Hopkinson pressure bar (SHPB) was utilized to investigate the high strain rate compressive behavior of CPB with dynamic loads of 0.4, 0.8, and 1.2 MPa. And the failure modes were determined by macro and micro analysis. CPB with different cement-to-tailings ratios, solid mass concentrations, and curing ages was prepared to conduct the SHPB test. The results showed that increasing the cement content, tailings content, and curing age can improve the dynamic compressive strength and elastic modulus. Under an impact load, a higher strain rate can lead to larger increasing times of the dynamic compressive strength when compared with static loading. And the dynamic compressive strength of CPB has an exponential correlation with the strain rate. The macroscopic failure modes indicated that CPB is more seriously damaged under dynamic loading. The local damage was enhanced, and fine cracks were formed in the interior of the CPB. This is because the CPB cannot dissipate the energy of the high strain rate stress wave in a short loading period.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The relevance vector machine (RVM) is considered a robust machine learning method and its superior performance has been confirmed through many successful engineering applications. To improve the ...performance of the RVM model, three single kernel functions, and three multikernel functions, including two newly proposed multikernel functions, tenfold cross-validation, and the hybrid particle swarm optimization with grey wolf optimizer (HPSOGWO) algorithm were combined to develop an artificial intelligence (AI) model framework. Afterwards, a new application of the RVM method was used and introduced for two different datasets of the blast-induced ground vibration. In addition, an artificial neural network (ANN) model and seven empirical equations were also developed for comparison purposes, and their prediction performances were evaluated considering three performance metrics, i.e., root mean square error (RMSE), correlation coefficient (
R
2
), and mean absolute error (MAE). The obtained results showed that the multikernel RVM model can provide better performance capacity than the single-kernel RVM model. As a result, the AI models were found to be more applicable than the empirical equations in estimating blast-induced ground vibration. The prediction performance results of these models confirmed that the selected database has a great impact on the prediction capacity. Therefore, it is a common act to compare the performance of various models based on the selected database before selecting an optimal predictive model. The proposed model in this study provides new theoretical and practical support for the prediction of blast-induced ground vibration and can be utilized by other researchers in similar fields.
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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
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
Surface ground motion produced by underground blasts is significantly influenced by near-surface geological conditions. However, near-surface low-propagation velocity layers were always ignored in ...past analyses of ground motions due to their thin thickness. With the rising concern about surface ground motions produced by the ascendant scale and frequentness of underground excavation and mining, close attention is gradually paid to ground blast vibrations. Therefore, systemic experiments were conducted and took seven months in an underground mine to clarify the variation of motion from underground rock to surface ground. The attenuation of surface ground peak particle velocities (PPVs) is compared to that in underground rock, and horizontal amplitudes are compared to vertical amplitudes. Differences between bedrock and surface ground vibrations are analyzed to illustrate the site effect of near-surface lower-propagation velocity layers. One-dimensional site response analysis is employed to quantify the influence of different geological profiles on surface ground vibrations. The experimental data and site response analysis allowed the following conclusions: (1) geological site effects mainly produce decreasing dominant frequency (DF) of surface ground vibrations; (2) the site amplification effect of blast vibration needs to be characterized by peak particle displacement (PPD); (3) shear waves (S-waves) begin to dominate and surface Rayleigh waves (R-waves) develop as blast-induced ground vibrations travel upward through rock and lower-velocity layers to the surface. The comparison of response relative displacement to a critical value is best to assess the potential for cracking on surface structures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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