Field Blast Research Articles

Influence of internal composition of fiber reinforced cement composites on resistance to near field blast

This paper describes the influence of internal composition of fiber reinforced cement composites on resistance to near field blast. The influence of multiple basalt meshes and dispersed fibers on a damage induced by a near-field blast is studied and numerically evaluated. Experimental measurements performed in the Boletice military area in 2014, 2015 and 2016 are evaluated by numerical simulations. The evaluation of the results is mainly focused on the stress in the cement composite, propagation of the overpressure caused by the blast and velocity of the ejected parts from the specimen. The influence of velocity of ejected parts coming out of the specimen, originally caused by the impact of a steel plate which bears TNT charges, is examined. And last, but not least, the influence of presence and position of basalt meshes in the specimen on its damage induced by delamination is also examined.

The impact of various types of steel fibres on the strength parameters and blast resistance of high – performance concrete

The paper describes composition proposals and subsequent optimization and testing of developed fibre-reinforced UHPC mixtures, which seem to be optimal as construction material for the blast and ballistic protective systems, such as mobile blast-resistant walls and covers, which are the expected outcomes of the presented research project. Methods of laboratory testing and optimization of developed UHPC mixtures, with the aim of achieving the best possible values of physical-mechanical parameters, are described in this paper. In connection with laboratory verification, field blast tests of UHPC board samples and consequently of the entire blast-resistant wall system were realized and resistance to dynamic stress was investigated.

Numerical study of fence type blast walls for blast load mitigation

A new fence type blast wall consisting of steel poles was recently proposed based on the idea that the blast wave-obstacle interaction could generate wave reflection, diffraction and out-of-phase interference to reduce the wave energy. The effectiveness of this kind of new blast wall in mitigating blast loading was investigated through 2D numerical simulations and field blasting tests. In this study, 3D numerical simulations are carried out as an extension of the previous studies for a more comprehensive understanding of the effectiveness of fence blast wall. The simulations are performed by using an explicit dynamic finite element analysis software AUTODYN 3D with validated material models. Responses of a reinforced concrete (RC) wall under blast load are also calculated for comparison. Influences of different parameters of the fence wall, including the cross-sectional shape of the steel poles, spacing between poles, number of fence layers and spacing between layers, on its effectiveness in mitigating the blast loadings are investigated. The peak overpressure, impulse and overpressure-time histories behind the fence and RC blast wall are compared with those in free field for evaluation. It is found that the fence blast wall, if properly arranged, could perform equally or even better than the RC wall in mitigating overpressure and impulse of blast wave. Moreover, fence blast wall is less likely to generate the secondary debris hazards associated with the RC and other solid walls when close-in explosion occurs. Therefore, it is an excellent alternative blast barrier in protecting critical structures in urban areas.

Effect of Excavation Blasting in Underground Water-Sealed Gas Storage Cavern Under In-Situ Stress

When underground caverns are created in deep rock masses by drilling and blasting methods, an undesirable excavation damage zone is induced. However, previous studies on effects of initial in situ stress field on blast-induced damage and safety criterion are few worldwide. In this study, we calculated and analyzed the dynamic response of surrounding rock during blasting excavation by the finite element software ANSYS/LS-DYNA based on field blasting tests of excavation blasting for underground gas storage caverns in Yantai, Shandong province, PR China. The numerical results indicated that tensile failure tended to occur in the middle of the curved wall. Meanwhile, the distribution and the range of surrounding rock damage under coupled static–dynamic load were obviously different with those under dynamic load alone, which showed that the influence of in situ stress on rock blast-induced damage could not be ignored. The relationship of the maximum tensile stress and peak particle velocity in the middle of the curved under in situ stress was analyzed and modeled. According to the maximum tensile strength theory and numerical calculation results, the critical vibration velocity was determined for controlling the rock damage of underground cavern, and the effects of the in situ stress on the safety criterion for rock damage were discussed.

Cross-section shape effects on anti-knock performance of RC columns subjected to air and underwater explosions

Columns are the key load-bearing elements in infrastructures. Common cross-section shapes of columns are square and circle. Those columns may be subjected to various blasting scenarios. This paper investigates the effects of cross-section shape on the anti-knock performance of RC columns subjected to air and underwater blast loads. The reliability of the fully coupled Lagrangian-Eulerian numerical model is verified by comparing with the results of the field blast test. The damage characteristics and dynamic response of the RC column with different cross-section shapes subjected to contact and close-in air explosions are investigated. The anti-knock performance of the RC column with different cross-section shapes subjected to contact and close-in underwater explosion is also studied. Nonlinear dynamic response behavior and damage mechanism of the RC column subjected to contact and close-in explosion are compared. The improvement effects of the reinforcement ratio and ultra-high performance concrete on the blast resistance of the underwater RC column are investigated. The results show that the cross-section shape has an important influence on the anti-knock performance of the column, whether subjected to air or underwater explosions. Employing circular cross-section can effectively improve the blast resistance of the column.

Experimental and numerical study on CFRP strip strengthened clay brick masonry walls subjected to vented gas explosions

A total of nine full-scale field blast tests were conducted in a specially designed reinforced concrete (RC) chamber to investigate the performance of carbon fiber reinforced polymer (CFRP) strip strengthened clay brick masonry walls subjected to vented gas explosions. Three wall specimens, i.e. unstrengthened, strengthened with distributed layout and strengthened with concentrated layout were prepared for blast tests. The testing data including overpressure time histories of vented gas explosions, displacement time histories, damage modes of each wall specimen were recorded and analyzed. It was found that under vented gas explosions, the wall specimen strengthened with concentrated layout showed improved blast resistance and all three wall specimens experienced typical flexural damage. Detailed micro models for masonry walls were developed in LS-DYNA, incorporating material parameters obtained from material tests. The accuracy of numerical models in predicting the responses of masonry walls was validated with the testing data. Parametric studies were conducted to explore the performances of masonry walls with different heights and thicknesses under blast loads specified by design codes. It was found that with the increase of wall thickness or the decrease of wall height, the maximum displacement and damage level of masonry walls decreased significantly. The 115 mm-thick masonry walls needed be strengthened to prevent collapse under the specified blast loads. The strengthened walls experienced typical flexural response and the strengthening effectiveness of using CFRP, GFRP and spray-on polyurea were numerically compared.

Generation of pressure–impulse diagrams for failure modes of RC columns subjected to blast loads

The Pressure–Impulse (P-I) diagram is generally accepted as a useful tool that permits easy assessment of structural responses to a specified load. To predict the failure characteristics of typical reinforced concrete (RC) columns subjected to blast loads, P-I diagrams considering different failure modes were generated with a high efficient procedure by employing an improved nonlinear analytical approach. In the nonlinear analytical approach that was improved from the Timoshenko beam theory, failure criteria to determine typical bending failure, diagonal failure and direct shear failure modes of RC columns were defined, respectively. The proposed efficient procedure was compiled to generate the P-I diagram by successively circular the improved nonlinear approach which was validated by conducting field blast tests. Parametric studies were carried out to investigate the effects on the failure characteristics of RC columns in the generated P-I diagram, including blast loads distribution, axial compression ratio, slenderness ratio, cross-section bend capacity and shear capacity. The analytical results demonstrate that the diagonal shear failure is most likely to occur on the typical RC columns subjected to blast loads. The bending failure basically occurred when the axial compression ratio and slenderness ratio of RC columns are large to a certain extent.

Numerical simulation of stress wave interaction in short-delay blasting with a single free surface.

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.

Micro-seismic event detection and location in underground mines by using Convolutional Neural Networks (CNN) and deep learning

Recent years have witnessed a clear trend to develop deeper and longer tunnels to meet the growing needs of mining. Micro-seismic events location is vital for predicting and avoiding the traditional mine disasters induced by high stress concentration, such as rock burst, roof caving, water inrush and slope landslide. Deep learning has become a research hotspot within the field of artificial intelligence in recent years, which has achieved significant progresses and applications in the areas of image recognition, speech recognition, language processing and computer vision. The biggest difference between the deep learning and the traditional back propagation training method is that the deep learning can automatically and independently learn the characteristics of a large amount of data without human intervention. This paper uses Convolutional Neural Network (CNN) and deep learning techniques to develop a method for identifying the Time Delay of Arrival (TDOA) and subsequently the source location of micro-seismic events in underground mines. The power spectrum and phase spectrum of cross wavelet transform calculated from the recorded seismic waves due to micro-seismic events are used as inputs to CNN. The amplitude and phase information of the cross wavelet transform power spectrum are parameters that are used without manual manipulation to build the complex mapping to predict TDOA by deep learning network. Experimental data from the in-field blast tests and simulation tests show that the proposed approach can well identify TDOA and hence detect the event source locations of the field blasting tests. It is demonstrated that the proposed approach with the CNN and deep learning techniques gives more accurate micro seismic source identifications with the recorded noisy waveforms from in-situ blast tests, as compared to several typical existing methods.

A study of cut blasting for one-step raise excavation based on numerical simulation and field blast tests

Over the past several decades, raise excavation has been widely employed in underground mining, civil engineering and military engineering. One-step raise excavation with burn cuts, where all the boreholes are pre-drilled and detonated at one time and no workers need to be underneath the freshly blasted and dangerous ground, is an important and promising method in raise excavation. Cut parameters, especially the parameters of prime cut which used empty hole as a free surface and swelling space, have significant influence on the effect of raise formed. In this study, two small-scale experimental methods, spiral hole spacing method and observation hole method, are designed to determine the prime cut parameters such as hole spacing (L), stemming length (Ls1, Ls2) and air deck length (La) which are normally determined by empirical formula. In order to study the feasibility of the two methods, numerical analysis and experimental tests are conducted in V zone of Sandaozhuang molybdenum mine (SMM), in which there are large numbers of underground goafs need to be controlled by filled raise. The Riedel–Hiermaier–Thoma (RHT) material model, which considers compression damage and tension damage effect under blasting loading, is employed in the LS-DYNA software to study the rock damage zone. Meanwhile, the field tests are carried out according to the two small-scale experimental methods. The comparison results show that the damage zone of numerical simulation has a good agreement with the experimental data. Further, the optimal prime cut parameters obtained from experimental tests are applied in one-step filled-raise excavation, and a 23 m raise that meets the design requirements is formed through the proposed technology. The results indicate that these cut parameters determined by the small-scale experiments are suited for one-step raise excavation. This study can provide two simple field experiments to determine the important prime cut parameters of one-step raise excavation.

Study on the long-hole raising technique using one blast based on vertical crater retreat multiple deck shots

Backfilling inaccessible cavity through raise can provide underground support for the active open-pit operations and the raise must be taken down in a single blast for safety reasons. Conventional raising techniques are not economically and technically feasible, and the maximum advance depth in one blast is limited. In this paper, small-scale crater tests were carried out in a site with cavities and field blasting test data were measured and evaluated to obtain the basic data for raise-scale blast designs. The raising design parameters with 250-mm hole diameter, including charge weight and height for each slice, slice height, hole spacing and delay interval, were derived. A scheme of multiple deck blasting based on vertical crater retreat (VCR) drop-raising method was designed for an abandoned cavity with 30-m cover. The lower 12-m cover was first blasted to investigate the practical blast performance. Charging and timing patterns were adjusted accordingly and the left 18-m cover was successfully opened up. Through raising tests, it is shown that the advantage of two available free surfaces up and down should be maximized, and smaller slice height and alternate initiation sequence are benefit for raising extension. A numerical model is then developed and it is calibrated against the 12-m raising test. By combining the calibrated numerical model with the raising test results, the effects of hole layout and in-slice delay are examined. It is shown that circular pattern and in-slice delay are positive for multiple-deck raising blast. Based on the foregoing analysis, the hole layout, charging and timing patterns are optimized. The optimized scheme was applied to field raising blast and a 32-m raise was successfully excavated in one blast.

Blast hazard impact on V-shape composite panel performance

The terrorist attacks have been increased during the last few years. Blast wave propagation is a great engineering challenge to protect structures such as vehicles and buildings. Mitigation systems used to protect the structures remain a sophisticated engineering problem.In this study, the V-shape composite structure is studied as a mitigation system to protect the bottom of vehicles against blast impact. The reviewed field blast test is used from another research conducted by Mazek et al.[1] to verify the proposed numerical model of the V-shape composite structures under blast effect. The numerical model is proposed by 3-D nonlinear finite element model (FEM).The displacement-time history of the V-shape composite (VSC) structure is presented as the blast wave propagates. The impact of the V-shape panel inclination on the V-shape composite structure performance is analyzed and presented under the blast effect. There is a good agreement between the results obtained by both the field blast test and the numerical model. The VCS structure improves the armored panel performance under the vehicles based on the impact of detonating different TNT explosive charges.

Blast Hazard Impact on V-Shape Composite Panel Performance

The terrorist attacks have been increased during the last few years. Blast wave propagation is a great engineering challenge to protect structures such as vehicles and buildings. Mitigation systems used to protect the structures remain a sophisticated engineering problem.In this study, the V-shape composite structure is studied as a mitigation system to protect the bottom of vehicles against blast impact. The reviewed field blast test is used from another research conducted by Mazek et al.[1] to verify the proposed numerical model of the V-shape composite structures under blast effect. The numerical model is proposed by 3-D nonlinear finite element model (FEM).The displacement-time history of the V-shape composite (VSC) structure is presented as the blast wave propagates. The impact of the V-shape panel inclination on the V-shape composite structure performance is analyzed and presented under the blast effect. There is a good agreement between the results obtained by both the field blast test and the numerical model. The VCS structure improves the armored panel performance under the vehicles based on the impact of detonating different TNT explosive charges.

Potential of transmission of Pyricularia graminis-tritici from plant to seed and from seed to seedling in wheat genotypes with different degrees of blast resistance

Abstract: Transmission studies of Pyricularia graminis-tritici by wheat seed can help establishing pathogen tolerance standards in crops. Four genotypes, each one with different responses to blast, were inoculated with five volumes of fungal suspension (1,5x105 spores.mL-1), in order to obtain 0, 5, 10, 20 and 30% of plants inoculated in the experimental unit. The potential of transmission of P. graminis-tritici from plant to seed was evaluated by the incidence of the fungus in the seeds produced. Under controlled conditions, the transmission rate of the fungus from seed to seedling was evaluated. Blast incidence in field allowed a high incidence of P. graminis-tritici in the seeds, especially in the genotypes considered susceptible. The transmission of fungus from the seeds to seedlings occurred 7, 14 and 21 days after sowing, at low rates. There was a relationship between the presence of blast in field and the incidence of P. graminis-tritici in seeds produced by the genotypes BRS 264, VI 98053, CD 116 and CD 104. Inoculation of 5, 10, 20 and 30% of plants with fungus can generate a high incidence of the pathogen in field and in the seeds produced, but it doesn`t guarantee a high transmission rate from seed to seedling, which is low under controlled conditions.

Long Term Temporal Changes in Structure and Function of Rat Visual System After Blast Exposure.

We identify long-term ocular sequelae subsequent to experimental blast exposure. Male Long-Evans rats were exposed to 230 kPa side-on primary blast overpressure using a compressed air driven shock tube. Visual system function and structure were assessed for 8 weeks after exposure using optokinetic nystagmus and optical coherence tomography. Vitreous protein expression and histology (TUNEL, H&E) were performed at 1 day and 1, 4, and 8 weeks. IOP was recorded bilaterally during blast in a subset of animals. Blast pressure profiles resembled the Friedlander waveform indicative of an open field blast. Peak IOP in directly-exposed eyes (240 kPa) was similar to peak blast overpressure, but IOP in indirectly-exposed eyes was 30% lower. Contrast sensitivity of blast-exposed animals decreased significantly by 20% 1 day after blast and did not recover by 8 weeks. Significant swelling and structural damage to the corneal epithelial and stromal layers were observed 2 weeks after blast exposure. Swollen corneas increased 254 ± 143 μm from baseline by 6 weeks, and scarring developed by 8 weeks. Histology revealed additional lens pathology 1 week after blast, suggestive of cataract development. Endothelial cell density increased significantly in blast-exposed animals between 1 and 4 weeks. Neurofilament heavy chain significantly increased after blast and returned to near baseline values by 8 weeks. Inflammatory cytokine changes corroborated ocular pathology findings. These data demonstrate immediate visual dysfunction and biochemical responses, but delayed structural pathology, in response to single primary blast exposure. The delayed pathology time course may provide a window to implement treatment strategies for improved visual outcome.

The role of a composite polycarbonate-aerogel face shield in protecting the human brain from blast-induced injury: A fluid–structure interaction (FSI) study

Background Blast-induced traumatic brain injury is the most prevalent injury sustained by combat soldiers at the frontline. The current study aims to investigate the effectiveness of composite polycarbonate-aerogel face shields with different configurations in mitigating blast-induced brain injuries. Method A series of dynamic fluid–structure interaction simulations of a helmeted head subjected to a frontal free field blast was performed, to evaluate the effectiveness of the current conventional polycarbonate face shield and three other composite face shields with different configurations when exposed to a frontal free-field blast. Results The simulation results demonstrated that the sandwiched structured face shields of polycarbonate and aerogel provided superior blast attenuation than a single-layered polycarbonate face shield. The alternate multi-layered transparent materials of high and low densities provided the best attenuation of blast pressure transmission to the head, with the polycarbonate exterior shell casing contributing to the structural integrity of the face shield, while the lower dense aerogel filler providing high acoustic impedance to blast wave transmission. Conclusion This study provides further insights on future development and design of personal protective equipment in mitigating blast-induced injuries to the head.

Impact and close-in blast response of auxetic honeycomb-cored sandwich panels: Experimental tests and numerical simulations

Protecting building, critical infrastructure and military vehicles from Improvised Explosive Devices (IEDs) has become a critical task. This study aims to examine the performance of a new protective system utilizing auxetic honeycomb-cored sandwich panels for mitigation of shock loads from close-in and contact detonations of high explosives. Both field blast tests and drop weight tests were performed using the proposed sandwiches asa shield for concrete panels in combination with conventional steel protective plates. The combined shield was found to be effective in protecting reinforced concrete structures against severe impact and close-in blast loadings. The honeycomb core with re-entrant hexagonal cells shows evident auxetic characteristics which contribute substantially to outstanding force mitigation and blast-resistance performances of such sandwich panels. Numerical simulations showed good agreement with the experimental results. The proposed auxetic panels were found to perform better than conventional honeycomb panels of the same size, areal density and material. Both were found to boost the energy absorption of the monolithic steel plate by a factor of 2.5 by changing its deformation pattern under close-in blast loading. In addition, a combination of the steel plate and an auxetic sandwich panel has aerial specific energy absorption (ASEA) higher than either of them, showing great potential for the development of lightweight blast protection of civil, mining, military, nuclear infrastructure and vehicles.

English

Rice blast caused by Magnaporthe grisea is an economically important disease which distributed in most rice growing areas of the world. Yield losses up to 100% are attributed to the blast disease in different rice growing regions of Uganda. In order to combat this disease screening of forty-six introduced Korean rice accessions and two checks IR-64 (resistant) and NERICA-1 (susceptible) were done in a 6 by 8 alpha lattice design in two replications under natural infestation in field conditions, and three replications in the screen house at National Crops Resources Research Institute (NaCRRI) of Uganda in 2015, A and B seasons. Final leaf blast severity, lesion size, area under disease progress curve (AUDPC) values, panicle blast and grain yield were highly significant among genotypes. Genotypes SRHB-133, SRHB-93 and SRHB-78 were resistant to rice blast in both field and screenhouse conditions and showed a lower lesion size. Therefore, these genotypes that consistently showed resistance to rice blast disease can be used as a source of resistance gene for rice blast. This leads to conclude that screening in both the field across seasons and confirming their resistance in the screen house helps the breeder to identify the genotypes that are truly resistant for further utilization as resistant sources. Key words: Rice blast, screening, Magnaporthe grisea, Uganda.

A study of RC bridge columns under contact explosion

This paper presents a study on reinforced concrete (RC) bridge columns under contact detonation. Two 1/3 scale RC bridge columns with circular and square cross-sections are studied both experimentally and numerically. Field tests were performed on two types of columns under 1 kg TNT contact explosion, and acceleration data at different heights of the columns were collected by accelerometers. Investigation of the damage evolution and structural local response is conducted by high-fidelity physics-based numerical models that are developed in the commercial program LS-DYNA through the Arbitrary Lagrangian–Eulerian (ALE) algorithm. The results from the numerical simulation are compared with the experimental results. Field blast tests showed that for both columns the cover concrete on the proximal and side surfaces close to the explosive charge suffered serious damage, while the cover concrete on the distal face remained almost intact. Due to the column geometry, the contact explosion caused larger blast loads on the square column leading to more severe damage. The damage mechanism of the two columns is discussed based on numerical simulations. The results from the numerical model match well with those from the tests except for the back-surface damage in both cases. Field data obtained from accelerometers also show reasonable agreement with results from the numerical modelling and confirm the localized structural response of the columns under contact blast loads. It is shown that the numerical models established in this study provide reliable predictions for the structural response of bridge columns under contact explosion.

Comparative evaluation of steel wire mesh, steel fibre and high performance polyethylene fibre reinforced concrete slabs in blast tests

Concrete is the most widely used construction material in the modern construction practice. Due to its relatively low tensile resistance, concrete tends to experience tensile failure and cracking under external loads. To enhance the tensile performance and ductility of concrete material, possible solutions including fibre reinforcement and steel mesh reinforcement are investigated in the present study. Steel fibre, ultra-high molecular weight polyethylene (UHMWPE) fibre and steel wire meshes were mixed with varying volume fraction in the concrete matrix. Static material tests including uniaxial compression and flexural bending tests showed that the steel fibre addition yielded better strength enhancement while UHMWPE fibre provided better material ductility. Concrete samples with hybrid steel fibre-steel mesh reinforcement showed high strength and ductility. Field blast tests are designed to study the behaviour of reinforced concrete slabs under close-in detonations. Different damage profiles are observed from the blast tests. The advantages and disadvantages of using different reinforcing materials are discussed. From the results, the advantages of replacing steel fibre with UHMWPE fibre or steel wire mesh were demonstrated.