Explosive Sources Research Articles

An adaptive mesh, GPU-accelerated, and error minimized special relativistic hydrodynamics code

ABSTRACT We present a new special relativistic hydrodynamics (SRHD) code capable of handling coexisting ultra-relativistically hot and non-relativistically cold gases. We achieve this by designing a new algorithm for conversion between primitive and conserved variables in the SRHD solver, which incorporates a realistic ideal-gas equation of state covering both the relativistic and non-relativistic regimes. The code can handle problems involving a Lorentz factor as high as 106 and optimally avoid the catastrophic cancellation. In addition, we have integrated this new SRHD solver into the code gamer (https://github.com/gamer-project/gamer) to support adaptive mesh refinement and hybrid OpenMP/MPI/GPU parallelization. It achieves a peak performance of 7 × 107 cell updates per second on a single Tesla P100 GPU and scales well to 2048 GPUs. We apply this code to two interesting astrophysical applications: (a) an asymmetric explosion source on the relativistic blast wave and (b) the flow acceleration and limb brightening of relativistic jets.

Inversion of explosive source land seismic data to determine source signature parameters

ABSTRACTIn seismic land exploration, where terrain conditions limit the use of vibrator sources, explosive sources are the preferred choice, and in situations where low‐frequency energy is essential, explosive is the preferred source, because it contains energy down to DC (0 Hz). I present a new method to estimate the source time functions of explosion source seismic data, using a modified acquisition method, data processing, modelling and inversion. Two shots of different sizes are fired into the same geophone spread with source–receiver geometry arranged such that the Green's functions are essentially the same. The spectral ratio of corresponding seismic traces is then the spectral ratio of the source time functions. A corresponding synthetic ratio filter is calculated from Blake's explosion source model for the sources within each pair. Each modelled source is defined by five parameters: the minimum radius a of the elastic zone, the internal pressure p0 at a, the density of the rock ρ and two elastic constants for an isotropic rock, the P‐wave velocity c and Poisson's ratio σ. A grid search finds the source parameters that minimise the difference between the measured and synthetic filters for each source pair, thus yielding the two source time functions, but not their absolute amplitudes. Deconvolution of the shot records within each pair for the minimum‐phase source time functions recovers the estimated earth impulse response gathers, convolved only with the response of the recording system. The improved knowledge of the source signature is then helpful in subsequent processing, especially for reverse time migration, full waveform inversion and amplitude‐versus‐offset analysis. I consider shots at different depths in the same shot hole and shots at the same depth in different shot holes. The former configuration minimises differences in geophone coupling, and, in operations, quality control procedures must be met. There is considerable variation in recovered source parameters from place to place, caused by variations in charge size, soil or rock properties and source coupling.

Study on the Coal Damage and Fracture Mechanism under Multiple Actions of Blasting Stress Wave

Controlled blasting technology is an effective way to enhance coalbed methane recovery, but the theoretical research has fallen behind engineering practice seriously. Therefore, in this work, based on the damage and fracture mechanics theory, the coal damage process and mechanism under the multiple actions of the blasting stress wave (BSW) were analyzed firstly. Then, the simulation experiment of coal damage accumulation was designed and carried out; during the experiment, the ultrasonic velocity of the samples was measured and the damage values were calculated. Under the multiple actions of BSW, the initial radial cracks around the blast-hole wall or in the area near the explosion source are formed under the action of tangential tension of BSW and the internal pressure of the blast-hole, and under the combined actions of stress wave, gas, and in situ stress, the primary cracks in the middle and far area of the explosion source expand and form the mesoscopic cracks because of the damage accumulation at the crack tip. And then the mesoscopic cracks grow and intersect to form a macroscopic crack. Finally, the macroscopic cracks expand and intersect with the initial radial cracks, the samples break suddenly under the load far below their fracture toughness because of the damage accumulation effects. Hence, the research results have guiding significance for better understanding and application of controlled blasting technology to enhance the CBM recovery.

An SVR-based Machine Learning Model Depicting the Propagation of Gas Explosion Disaster Hazards

Shock wave pressure, high temperature flames, and toxic gases are among the factors that cause mine ventilation system failure following a gas explosion. Herein, we propose a Support Vector Regression (SVR)-based machine learning model to quickly determine the propagation of these disaster-causing hazards throughout the whole ventilation network. FLACS was used to simulate the explosions in a straight roadway with different spatial geometric parameters and gas explosion equivalents. Four SVR machine learning models were constructed by incorporating the roadway’s cross-sectional area, length of gas filling, gas concentration, and the distance between the observation point and the explosion source as inputs, while the shock wave pressure, flame temperature, time to the maximum temperature, and pressure served as outputs. The proposed model can quickly and accurately predict the propagation of disaster-causing hazards for a given explosion position and equivalent. As such, it plays a significant role in determining the ventilation system failure mode and aids decision makers and rescuers in developing a rescue and refuge plan.

Analysis of Fractal Features of Blasting Vibration Signal Based on EEMD Decomposition

In order to study the propagation characteristics of blasting seismic waves by using the analysis and research of blasting vibration monitoring data of Urumqi subway tunnel excavation, the blasting vibration signal has been decomposed into several IMF components by EEMD decomposition and fractal theory has been used to calculate the correlation dimension in this paper. The results show that the IMF component can reveal the frequency characteristics in the blasting vibration signal clearly. As the measuring point is far away from the explosion source, the complexity of the frequency component of the vibration signal gradually decreases. The seismic wave interacts with the rock and soil medium in the propagation process, make it shown non-linear characteristics, which are not easily to be observed by conventional measure methods. This paper introduces fractal dimension to study the nonlinear characteristics of blasting vibration signals and achieves the purpose of analysing the law of blasting seismic wave propagation. This study achieves a quantitative description of the effects of site media on seismic waves, and at the same time, it lays a theoretical foundation for predicting the vibration effect analysis of seismic waves reaching the target position.

Estimation of bottom parameters in the New England Mud Patch using geophone and hydrophone measurements

Measurements of acoustic pressure and particle velocity were made during the Seabed Characterization Experiment (SCEx) in the New England Mud Patch south of Cape Cod in about 70 m of water. The University of Rhode Island and Woods Hole Oceanographic Institution deployed the “geosled” with a four-element geophone array, a tetrahedral array of four hydrophones, and Several Hydrophone Receive Units (SHRUs) as data acquisition packages. In addition, a recently developed low frequency source, the interface Wave Sediment Profiler (iWaSP), was deployed to excite interface waves (Scholte waves) on the seabed. The geophone array was localized using the known locations of the small explosive sources and noise from the research vessel. Modal arrivals from broadband sources on geophones and hydrophones were used to invert for compressional and shear wave speeds and attenuation in the mud layer and the underlying sand layer. The Scholte wave arrivals from the iWaSP source measured by the geophone array also provided estimates for these parameters. The inversion results are compared to modeling using the viscous grain shearing (VGS) theory. [Work supported by the Office of Naval Research, Code 322 OA.]

Retrieving reflection arrivals from passive seismic data using Radon correlation

AbstractSince explosive and impulsive seismic sources such as dynamite, air guns, gas guns or even vibroseis can have a big impact on the environment, some companies have decided to record ambient seismic noise and use it to estimate the physical properties of the subsurface. Big challenges arise when the aim is extracting body waves from recorded passive signals, especially in the presence of strong surface waves. In passive seismic signals, such body waves are usually weak in comparison to surface waves that are much more prominent. To understand the characteristics of passive signals and the effect of natural source locations, three simple synthetic models were created. To extract body waves from simulated passive signals we propose and test a Radon-correlation method. This is a time-spatial correlation of amplitudes with a train of time-shifted Dirac delta functions through different hyperbolic paths. It is tested on a two-layer horizontal model, a three-layer model that includes a dipping layer (with and without lateral heterogeneity) and also on synthetic Marmousi model data sets. Synthetic tests show that the introduced method is able to reconstruct reflection events at the correct time-offset positions that are hidden in results obtained by the general cross-correlation method. Also, a depth migrated section shows a good match between imaged horizons and the true model. It is possible to generate off-end virtual gathers by applying the method to a linear array of receivers and to construct a velocity model by semblance velocity analysis of individually extracted gathers.

Impulse Processing Algorithm for Random Source Signals of Roadheaders That Is Based on Compound Interferometry

The boom-type roadheader is the main equipment for realizing the mechanization of coal drifting in coal mines, and it is an indispensable production equipment in major coal-producing countries. Substantial vibrations are generated during the operation of a roadheader; these vibrations carry substantial energy and, thus, can be regarded as a potential source and used for seismic advance detection purposes in mine drifts. Compared with a conventional exploration source, a roadheader source produces a complex continuous random signal. The shape of a seismic wavelet is uncertain and its duration is relatively long; thus, it must be processed into a conventional pulse signal before it can be used for subsequent processing and analysis. Therefore, based on the advantages of seismic interferometry in random signal processing, two seismic interference techniques, namely, deconvolution and cross-correlation, are introduced for constructing a compound interference algorithm. On the basis of a theoretically derived formula, a random signal impulse processing experiment is conducted using field-acquired source signals from a roadheader; this approach resolves the problem that cross-correlation alone cannot yield ideal results. Hence, a feasible algorithm for the impulse processing of a random signal, namely, the compound interference algorithm, is proposed. The algorithm deconvolves each seismic trace to obtain the reference trace and other receiver traces after compressing the wavelet. Then, the reference trace and each receiver trace are cross-correlated, and the wavelet time delay information of each correlated wavelet pulse, namely, the wavelet time delay information of the receiver trace relative to the reference trace, is obtained. Accordingly, the direct wave and reflected waves are recognized. To evaluate the performance of the algorithm, an algorithm application experiment is conducted for another group of random source signals that were collected by a roadheader under different coal drift conditions. Again, the algorithm processing results are consistent with the single-shot record characteristics of an explosive source. Consequently, the proposed algorithm can satisfy the requirements for engineering exploration and analysis. A comprehensive analysis further demonstrates that the compound interference algorithm is both feasible and effective and that the processed seismic signals can be used for subsequent processing and interpretation.

Discharge and ignition characteristics from indentation fracture of coal mine roof

Electric effects are generated during the deformation and fracture of coal mine roof sandstones. Previous research has mostly focused on the mechanism of electric effect generation and the electromagnetic radiation released. However, few studies have investigated the hazard characteristics of the high-energy electrons released. This study explores the discharge and ignition characteristics of roof indentation fracture to identify the real ignition source of a gas explosion in a coal mine goaf. Theoretical and experimental analyses conclude that the charge of the coal mine roof sandstone will gradually escape from the surface during the loading process. The charge release process of the rock before fracture is related to the loading rate, and an instantaneous high voltage will be formed during fracture of the rock. The compressive strength of the rock plays a key role in this type of instantaneous discharge process. An electric spark can be generated at the moment of rock fracture under loading. The high-energy electrons released by rock deformation and rupture can ionise the air. Moreover, the electric spark can persist for more than 20 ms, which considerably exceeds the induction period for gas ignition. When the quartz content of the roof rock is high and reaches a certain compressive strength, stress mutations can cause the roof to undergo instantaneous rupture and generate electric sparks. The premixed gas air gathered in the area is thus broken down and ionised, igniting the gas and producing a gas explosion.

Risk-based quantitative method for determining blast-resistant and defense loads of petrochemical buildings

Petrochemical buildings are usually distributed near chemical installations and have a high risk of explosion because of the concentration of people. In order to effectively design and protect buildings against explosion, it is needed to determine the blast-resistant and defense loads reasonably. Based on the theory of risk, a triangular pyramid explosion risk model was established in this study, which combined the overpressure p, duration t, and frequency f of the explosion scene at the same time. The first principle of “acceptable cumulative frequency” and the key principle of “maximum explosion risk” were formulated. According to this method, the explosion risk of eight leakage units with 10 groups of leakage hole size and three dangerous wind directions were obtained. According to the cumulative explosion frequency curve and the explosion risk curve, blast-resistant and defense loads of the four walls were determined quantitatively. Among the four walls, the explosion overpressure were 44.0–74.5 kPa, and the corresponding duration were 34.1–39.1 ms. The cumulative explosion frequency were 2.11E−5 to 8.58E−5 times annually. The explosion risk value were 3.64E−3 to 5.35E−3 kPa·ms annually. The results indicated that it was of great importance for the calculation of the explosion risk to reasonably divide the leakage unit and determine the leakage frequency. The explosion scene and its frequency, the volume of the obstructed region, and the distance of the explosion source were the key variables that affected the explosive load. The final blast-resistant and defense load values were found in the case of the middle hole size leakage. Blast-resistant and defense loads not only met the risk acceptance standard but also considered the overpressure and the duration of explosion. At present, they have been extensively applied in the blast-resistant design and engineering transformation of buildings in SINOPEC.

Model for Calculating Seismic Wave Spectrum Excited by Explosive Source

To reveal the characteristics and laws of the seismic wavefield amplitude‐frequency excited by explosive source, the method for computing the seismic wave spectrum excited by explosive was studied in this paper. The model for calculating the seismic wave spectrum excited by explosive source was acquired by taking the seismic source model of spherical cavity as the basis. The results of using this model show that the main frequency and the bandwidth of the seismic waves caused by the explosion are influenced by the initial detonation pressure, the adiabatic expansion of the explosive, and the geotechnical parameters, which increase with the reduction of initial detonation pressure and the increase of the adiabatic expansion. The main frequency and the bandwidth of the seismic waves formed by the detonation of the explosives in the silt clay increase by 23.2% and 13.6% compared to those exploded in the silt. The research shows that the theoretical model built up in this study can describe the characteristics of the seismic wave spectrum excited by explosive in a comparatively accurate way.

Lower turning point convegence zone in deep water with an incomplete channel

In a deep sea sound channel, rays will bend due to the sound speed profile, and convergence zone will occur when the rays are intensive. Transmission loss in the convergence zone is smaller and it is conducive to acoustic detection and communication. Therefore the study of acoustic characteristics in convergence zone is always the focus of deep-sea acoustics. A long-range sound propagation experiment is conducted in the South China Sea. An equivalent broadband explosive sound source of 1 kg is placed at a depth of 200 m, and the hydrophone receives the data at 3146 m far. The processing and analysis of the experimental data indicate that there is a convergence zone below the sound channel axis in the incomplete deep channel. Compared with the upper turning point convergence zone near the surface, this convergence zone has a high convergence gain at a long distance. The caustic lines of refracted type and refracted surface-refleted type are determined by means of ray-normal mode theory. It is found that the location of the deep convergence zone observed in the experiment is consistent with the position of the refracted caustic line. It is proved that the convergence zone is a lower turning point convergence zone formed by the superposition of a large number of normal modes in the same phase, and it has a convergence effect at a certain depth below the sound channel axis in the deep sea. The formation conditions of the convergence zone and the influence of sound source depth on the caustic structure of the convergence zone are studied. The comparisons of the transmission loss and the width between the upper and lower turning point convergence zone at a long distance aremade. The analysis shows that the convergence gain in the seventh lower turning point convergence zone is still no less than 10 dB. The influence of the vertical structure of sound velocity on the lower turning point convergence zone is studied. The theoretical analysis results are in good agreement with the experimental data.

Experimental Research on the Electric Spark Bubble Load Characteristics under the Oblique 45 Degree Curved Surface Boundary

In order to study the influence of the pressure load generated during the pulsation of cavitation bubbles on the oblique 45-degree curved surface boundary. The curved surface boundaries have different curvatures. This study also designs a multi-angle bracket to make the oblique boundary oblique 45 degrees. This research uses high-voltage electric discharge to generate electric spark bubbles, which act as cavitation bubbles. When the explosion source is at different distances from the oblique 45-degree boundary, a high-speed camera is used to capture the pulsation process of electric spark bubbles. A pressure sensor is used to measure the pulsating load of the electric spark bubbles on the oblique 45-degree boundary during the pulsation process. In this study, we use the dimensionless parameter ζ to represent the curvature of the oblique 45-degree boundary. The dimensionless parameter γ is used to represent the shortest distance between the explosion source and the oblique 45-degree boundary. It is found through experiments that the oscillation characteristics and pulsating load of electric spark bubbles will be affected by ζ and γ. This study summarized six types of unique bubble pulse shapes from 44 groups of experiments. They are “mushroom shape without jet”, “mound shape with jet”, “jellyfish shape with jet”, “oval shape with jet”, “drop shape without jet”, and “spherical shape without jet”. In this paper, the ABAQUS/Explicit is used to simulate the ring-shaped bubble that is not clearly captured by the high-speed camera. Finally, the study summarizes the shock wave load generated during the explosion, the first pulsation load, and the second pulsation load of electric spark bubbles, and finds an obvious overall trend of change.

A study on source identification of gas explosion in coal mines based on gas concentration

When the gas explosion occurs in the mine, it is essential to determine in time whether the ventilation system is damaged and trace the explosion location and time to develop an emergency rescue plan and conduct rescue work. In this study, a method to trace the source of explosion by monitoring catastrophic gas concentrations, based on the one-dimensional unsteady flow differential equation, an unsteady flow model for the transport of catastrophic gas in the ventilation network was established. Further, the change laws of catastrophic gas concentrations at roadway intersections were analyzed in combination with the nodal air volume balance law in the ventilation network theory. Finally, we used the particle swarm optimization (PSO) algorithm to invert the gas explosion source point and time in conjunction with the catastrophic gas concentration monitoring data at the monitoring point. Herein, an instantaneous release tracer gas was used instead of a catastrophic gas after a gas explosion, and a concentration monitoring experiment was carried out in a full-size experimental roadway. The inversion results show that the PSO can invert the location and time of the explosion source and simultaneously assess the damage status of dampers within the ventilation network. Note that the root mean square error between the inversion and measured results was less than 1, proving the reliability of the inversion results.

Propagation of gas explosions of different volumes in a large test tunnel

ABSTRACT With the continuous development of coal science and technology, gas explosion disasters have become an important factor in restricting efficient and intensive coal mining which threaten safe production in coal mines. In a large test tunnel, gas explosion propagation tests were conducted by taking gas-air mixtures with different volumes of 50 m3, 100 m3, and 200 m3 as explosion sources. The results demonstrate that, at a given gas concentration, the larger the volume of the gas-air mixture, the stronger the explosive power and the further the flame propagates. The pressure near the explosion source does not necessarily the maximum value in the whole gas explosion process. In the increasing propagation distance, explosion pressure does not linearly attenuate but fluctuates along the tunnel. The flame propagation velocity increases and then decreases throughout the explosion in three stages: a slow propagation stage at the beginning of an explosion, an accelerated propagation stage, and a decelerated propagation stage before flame extinction. Shock waves generated by a gas explosion interact and influence explosion flames and there is a positive feedback mechanism that promotes their mutual interaction. The conclusions provide an important theoretical basis for preventing gas explosion accidents and formulating active measures for explosion suppression in underground coal mines.

Numerical Simulation of the Dynamic Responses and Cumulative Damage of Underground Caverns under Multiple Explosions

Attacking underground caverns with earth-penetrating bombs usually involves multiple explosions in succession. To assess the dynamic responses and cumulative damage of underground caverns under multiple explosions, based on a reduced-scale physical model test, the modified Riedel–Hiermaier–Thoma (RHT) model in the finite-element software LS-DYNA is used to build an underground cavern model that encounters four explosions above the vault. The characteristics of the stress wave attenuation and the evolution laws for the cumulative damage of the surrounding rock in the process of the four explosions are presented. Also, the displacement of the vault, the strain of the cavern wall, and the damage of a rock bolt-supported cavern and an unanchored cavern are compared. The results indicate that the peak pressure is attenuated increasingly in the latter three explosions. The circumferential strain of the cavern wall changes from tensile to compressive from the vault to the corner. The damage of the surrounding rock on the left and right sides of the explosion source is attenuated with increasing distance from the explosion source, and the attenuation curve has a reverse “S” shape. Moreover, the attenuation rate of the curve decreases with each explosion. Multiple explosions do not affect the size of the crushed zone, but they do increase the range of the fracture zone. With each explosion, the cumulative damage of the surrounding rock increases irreversibly, but the damage increment decreases. The cumulative damage of the surrounding rock exhibits a highly nonlinear relationship with successive explosions, and the effect of the rock bolt reinforcement becomes more obvious with successive explosions. Accordingly, the present research results offer a reference for antiexplosion design and support the optimization of underground engineering.

Seismo-Acoustic Characterization of Mount Cleveland Volcano Explosions

Volcanic explosions can produce large, ash-rich plumes that pose great hazard to aviation, yet may often have few precursory geophysical signals. Mount Cleveland is one of the most active volcanoes in the Aleutian Arc, Alaska (United States) with at least 65 explosions between December 2011 and June 2020. We characterize the seismo-acoustic signals from explosions at Mount Cleveland over a period of 4 years starting in 2014 when the permanent local instrumentation was installed. While the seismic explosion signals are similar, the acoustic signals vary between explosions. Some explosion acoustic waveforms exhibit a single main compressional phase while other waveforms have multiple compressions. The time lag between seismic and acoustic arrivals varies considerably (up to 2.20 s) at a single station ∼3 km from the vent, suggesting a change in propagation path for the signals between explosions. We apply a variety of methods to explore the potential contributions to this variable time lag from atmospheric conditions, nonlinear propagation, and source depth within the conduit. This variable time lag has been observed elsewhere, but explanations are often unresolved. Our results indicate that while changes in atmospheric conditions can explain some of the variation in acoustic arrival time relative to the seismic signal arrivals, substantial residual time lag variations often still exist. Additionally, nonlinear propagation modeling results do not yield a change in the onset time of the acoustic arrival with source amplitudes comparable to (and larger) than Cleveland explosions. We find that a spectrum of seismic cross-correlation values between events and particle motion dip angles suggests that a varying explosion source depth within the conduit likely plays a dominant role in the observed variations in time lag. Explosion source depths appear to range from very shallow depths down to ∼1.5–2 km. Understanding the seismo-acoustic time lag and the subsequent indication of a variable explosion source depth may help inform explosion source modeling for Mount Cleveland, which remains poorly understood. We show that even with a single co-located seismic and acoustic sensor that does not always remain on scale, it is possible to provide meaningful interpretations of the explosion source depth which may help monitoring agencies understand the volcanic system.

Effects of Secondary Sources of Underground Nuclear Explosions on the mb : Ms Criterion and Implications for Discrimination of the DPRK’s Nuclear Tests

ABSTRACTThe mb : Ms (mb vs. Ms) relationship is an important criterion for screening explosions from earthquakes and has been widely adopted in seismological monitoring by the Comprehensive Nuclear-Test-Ban Treaty Organization. In general, the earthquakes have larger Ms than the underground explosions with equivalent mb. However, it has been reported that this recognition criterion failed to identify some explosions at the North Korea nuclear test site. In this study, we investigate the potential effects of secondary source components, including the compensated linear vector dipole (CLVD) and double-couple (DC) sources, on mb and Ms magnitude measurements and the physical mechanism of the mb : Ms recognition criterion by calculating synthetic seismograms. The results show an apparent critical body-wave magnitude of 5 when using the mb : Ms method to discriminate North Korean underground nuclear explosions. The Ms measurements decrease as the CLVD components increase, whereas the effects from the DC source can be neglected. Small events, such as the first five North Korean nuclear tests, generate weak CLVD components, leading to the failure of mb : Ms-based discrimination, whereas the last event, with a larger magnitude, caused extensive damage and hence can be successfully discriminated. In addition, the large difference between the source spectrum of explosions and those of earthquakes might be another important factor in the successful mb : Ms-based discrimination of the sixth North Korean nuclear test.

Numerical simulation of the dynamic responses and damage of underground cavern under multiple explosion sources

Underground caverns are often subjected to multiple explosions, and the stress wave interaction caused by multiple explosion sources is very complicated. To evaluate the effects of possible explosions around an underground cavern, based on a similarity model test, the finite element software LS-DYNA3D was utilized to analyze the dynamic responses and damage of underground cavern under seven combinations of concentrated charge explosion sources in three places, including the side of the vault, side arch, and sidewall. The propagation law of the blast-induced wave, the formation mechanism of the crack, and the displacement distribution characteristics of the surrounding rock were presented, and the damage of the cavern was described according to the peak displacement and peak particle velocity (PPV) of the measurement points located on the cavern wall. Besides, the effects of rock bolt reinforcement on the anti-blast performance of the cavern were also studied. The research results indicate that when the compressive wave propagates to the free surfaces of the ground and cavern, it will reflect and generate the tensile wave, and then the tensile wave will cause spalling in the surrounding rock. Due to the interaction of the tensile wave, different forms of crack will occur in the surrounding rock. The main difference of the crack distribution between the single explosion source cases and multiple explosion sources cases lies in the middle part of the two explosion sources. The stress wave intensity, peak displacement, and PPV of the surrounding rock at the superposition of stress waves are obviously larger than those of other rock mass. The peak displacement, PPV, and damage of the surrounding rock increase with the increasing explosion source number. Furthermore, the damage assessment of the cavern evaluated by the single degree of freedom (SDOF) method agrees well with the result of the PPV empirical damage criteria. Compared with the unanchored cavern, the peak displacement of the bolt-supported cavern is significantly reduced, and the crack development changes from transverse to axial along the rock bolt direction in the reinforced area, and the blast-resistant performance of the surrounding rock is improved. The research results can provide valuable references and basis for the anti-explosion design of underground defensive projects.

One-step estimation method and nomogram to predict safety distances of pressurized gas pipelines from blast sources

Pressurized gas pipelines may be endangered by accidental or intentional activities causing excess ground vibrations leading to failure. Thus, many papers have been published on this issue, yet most of these efforts suffer from complexity and inability to ascertain that all engaged factors are taken into account. These factors are attributed, namely, to explosion source, explosion-ground interaction, energy transfer through the ground, ground-pipeline interaction, and response of the pipeline. The deterministic method developed previously by the author has derived useful prediction mathematical formulas that can be used to calculate, either the stand-off distance of purposefully used explosives, or the maximum quantity of explosives to be used at a given distance, or the equivalent stress of a pipeline induced by an explosive charge at a given standoff distance. The method can also be applied to accidental blast events in factories or other activities. Yet, the complex formulas developed are hard to be used in the field and a simpler approach is needed to facilitate and accelerate in-field estimations. Thus, a nomogram was prepared to make the safety estimations easy and fast and taking into account all engaged critical factors starting from the explosion source through the integrity of the structure.