Underground Explosions Research Articles

A study of explosive-induced fracture in polymethyl methacrylate (PMMA)

The fracture response of geologic materials is of interest for applications, including geothermal energy harnessing and containment of underground explosions. To better understand the explosively induced fracture response of geomaterials, polymethyl methacrylate (PMMA) was used as a transparent rock surrogate to allow imaging of internal shock propagation and fracture growth processes. Experiments were conducted using high-speed shadowgraphy and photon Doppler velocimetry (PDV), which were compared to numerical simulations. Experiments measured fractures produced in 304.8mm×304.8mm×304.8mm PMMA cubes with two simultaneously initiated detonators. The cubes were subjected to varying amounts and directions of externally applied uniaxial stresses, including no stress, 2 MPa stress, and 20 MPa stress. The fracture radius as a function of time was extracted from the high-speed videos. Post-test images of the PMMA cubes aided in the determination of three-dimensional effects not directly imaged by the cameras. The surface velocity history and the shock response captured in PDV and the high-speed videos were compared to the simulated explosive-induced shock response. The simulation results indicate that the shock drives the fracture for the first 20 μs corresponding to a fracture radius of approximately 15 mm in the experiments. The gas-driven fracture extent was estimated analytically using an equilibrium stress distribution calculated after the shock wave propagation through the sample. Reduction in the gas pressure due to the leakage of the explosive products through the crack as a function of time was accounted for. The estimated fracture lengths were in agreement with the experimentally observed fracture lengths.

‘Dancing in the halls of the rich’? Fatal mine explosions and pro-employer bias in the UK mining inspectorate, 1870-1900

ABSTRACT Did government mines inspectors in late Victorian Britain display overt bias towards employers when assigning blame for fatal underground explosions? Inspectors were closer to managers and coal owners than they were to miners or mine supervisors in terms of status, background, and engineering experience. That inspectors had more in common with management could have led to favouritism or regulatory capture, as was suggested at the time by miners and more recently by historians. To adjudicate these claims, this article applies the technique of qualitative content analysis to the comments of mines inspectors in their published annual reports. The findings reveal that inspectors frequently condemned employers and their representatives, especially after gas and coal dust explosions that took 10 or more lives. By contrast, following blasting explosions, which typically killed only one person, they usually blamed the miners themselves. The available evidence therefore suggests that any discernible pro-employer bias on the part of the inspectorate was limited to smaller explosions where it was easier to ignore systemic factors and deem individual workmen to be at fault.

Intelligent Anti-Seismic Foundation: The Role of Fractal Geometry

Safe and resistant infrastructure is an essential component of public safety. However, existing structures are vulnerable to damage resulting from excessive ground movement due to seismic activity or underground explosions. The aim of this paper, which is part of an extensive study, is to develop an isolation system based on periodic materials with H-fractal geometry in order to obstruct, absorb or completely modify the pattern of seismic energy before it reaches the foundations of structures. Fractal metamaterial structures have shown promise for increasing the frequency range prohibited for seismic protection. We report the anti-seismic properties of a seismic metamaterial model based on an H-shaped quasi-fractal cell. The fractal design, also known as seismic metamaterials, has an important impact on the band structures of seismic crystals. Using the fractal as a base unit, anti-seismic phononic crystals were developed, and their band-gap characteristics were shown to display unique features due to the increasing wave propagation path and hybridization between local resonances and Bragg scattering. The seismic–mechanical duality is supposed to provide flexible solutions capable of increasing/widening the band-gaps to improve the level of seismic protection.

Explosion and vented explosion behaviors of low-concentration gas in large-scale pipes

The extraction, transmission, and use of low-concentration gas in coal mines are often challenged by potential accidents due to proximity to the combustion and explosion concentration limit. Water sealing of fire barriers and explosion venting devices guarantee the safe transmission of low-concentration gas. The propagation and venting of gas explosion under different concentrations are experimentally investigated in a DN500 mm pipe explosion propagation test system. The water sealing of fire barrier vented explosion field evolution of methane-air mixture at the stoichiometric concentration (9.5 vol%) is examined through Fluent numerical simulation to reveal the water sealing of fire barrier further vented explosion pattern of gas transmission pipelines under low concentrations. The explosion overpressure and flame propagation of low-concentration gas in pipes are observed and correlated. Based on their coupling relationship, the design basis for the installation location of the explosion venting device is derived. The vented explosion characteristics of low-concentration gas during pipe transmission are summarized, proving that this explosion venting technique enhances both the explosion venting device and explosion parameters. Our observations and analysis can offer useful clues to underground gas explosion and prevention in coal mines.

Numerical modeling of the damage mechanism of concrete-soil multilayered medium subjected to underground explosion using the GPU-accelerated SPH

The prediction of the damage mechanism of the concrete-soil multilayered medium subjected to underground explosion is a challenging task to address. In this paper, the smoothed particle hydrodynamics methodology is introduced to deal with the soil fragmentation and fracture propagation in concrete which are involved in the physical process of explosion in this double-layered medium. The Drucker–Prager constitutive model and the Holmquist–Johnson–Cook concrete constitutive model are employed to describe the dynamic behavior of the soil and concrete, respectively. Firstly, the numerical model was validated by two cases, namely the high velocity impact of an aluminium sphere on a concrete plate and the fracture propagation of rock medium under blast loading. Subsequently, the explosion in the three-dimensional concrete-soil multilayered medium involving millions of particles was simulated and investigated using GPU-accelerated smoothed particle hydrodynamics methodology. The numerical results obtained using smoothed particle hydrodynamics are compared against the available experimental data, which shows that the present SPH model can reproduce the failure pattern and fracture propagation of the concrete medium with cylindrical hole in the concrete plate and different burial depths of the explosive.

Experimental study of the dynamic responses of surrounding jointed rock masses and adjacent underground openings and induced ground vibrations subjected to underground explosion

The shock wave generated after underground blasting might lead to severe catastrophe or irreparable destruction of adjoining underground and ground structures. To investigate the dynamic response of rock masses and adjacent underground openings and induced ground vibrations subjected to underground blasting, a sequence of laboratory tests was implemented with explosive charges and cement mortar blocks. The results show that not only the charge loading density but also the joint orientation affect the ground peak particle velocity (PPV) in a significant way, as well as the first peak strain at the neighbouring opening and in the surrounding rock masses. The first peak strain of the rock masses has a rising tendency with increasing charge loading density or decreasing scaled distance. The PPV on the ground clearly increases with increasing charge loading density. The first peak strain of the rock masses and ground PPV are dominated by the wave path, which is determined by the relative locations of the explosion source, measuring point and joints. The principal frequency of ground vibrations shows an increasing trend with increasing joint orientation, while the charge loading density slightly impacts the principal frequency. These research findings could enhance the comprehension of blasting wave propagation through jointed rock masses and contribute to the stability evaluation of aboveground and underground structures subjected to underground explosions.

Assessment of Change in Rock Mass Permeability in the Vicinity of Underground Explosion from Experimental Data and Numerical Modeling

Assessment of Change in Rock Mass Permeability in the Vicinity of Underground Explosion from Experimental Data and Numerical Modeling

The Borderlands

The Borderlands

Explosion or Tectonic Earthquake? Evidence That an ML 3.7 Seismic Event Occurred near North Korea’s Nuclear Test Site on 11 February 2022

Abstract Discriminating between tectonic earthquakes and underground explosions in the monitoring of possible underground nuclear tests has become more challenging following the increase in seismicity at the Punggye-ri nuclear test site after North Korea’s sixth nuclear test conducted in 2017. In this article, we discuss how to distinguish between explosions and moderate-magnitude tectonic earthquakes around the Punggye-ri test site. For an ML 3.7 seismic event that occurred near the Punggye-ri test site on 11 February 2022, we precisely relocated the source epicenter, determined the possible depth, identified the P first motions, measured the P/S amplitude ratios, and compared the seismic waveform details with those of North Korea’s historical nuclear test explosions and tectonic earthquakes. The results showed that (1) the epicenter is farther away from the tunnels under Mt. Mantap, and no tunnel entrances and shafts are found around the epicenter in the latest satellite images; (2) the source depth is 5.5 km, which is greater than the ordinary depth of underground nuclear tests; (3) negative P first motions were observed; (4) the P/S amplitude ratios are significantly different from those of North Korea’s previous nuclear tests; and (5) the waveform details are similar to previous tectonic aftershocks rather than historical nuclear test explosions. Our findings suggest that this seismic event was a tectonic earthquake rather than an underground explosion.

The influence of physical and algorithmic factors on simulated far-field waveforms and source–time functions of underground explosions using unsupervised machine learning

SUMMARY Characterizing explosion sources and differentiating between earthquake and underground explosions using distributed seismic networks becomes non-trivial when explosions are detonated in cavities or heterogeneous ground material. Moreover, there is little understanding of how changes in subsurface physical properties affect the far-field waveforms we record and use to infer information about the source. Simulations of underground explosions and the resultant ground motions can be a powerful tool to systematically explore how different subsurface properties affect far-field waveform features, but there are added variables that arise from how we choose to model the explosions that can confound interpretation. To assess how both subsurface properties and algorithmic choices affect the seismic wavefield and the estimated source functions, we ran a series of 2-D axisymmetric non-linear numerical explosion experiments and wave propagation simulations that explore a wide array of parameters. We then inverted the synthetic far-field waveform data using a linear inversion scheme to estimate source–time functions (STFs) for each simulation case. We applied principal component analysis (PCA), an unsupervised machine learning method, to both the far-field waveforms and STFs to identify the most important factors that control variance in the waveform data and differences between cases. For the far-field waveforms, the largest variance occurs in the shallower radial receiver channels in the 0–50 Hz frequency band. For the STFs, both peak amplitude and rise times across different frequencies contribute to the variance. We find that the ground equation of state (i.e. lithology and rheology) and the explosion emplacement conditions (i.e. tamped versus cavity) have the greatest effect on the variance of the far-field waveforms and STFs, with the ground yield strength and fracture pressure being secondary factors. Differences in the PCA results between the far-field waveforms and STFs could possibly be due to near-field non-linearities of the source that are not accounted for in the estimation of STFs and could be associated with yield strength, fracture pressure, cavity radius and cavity shape parameters. Other algorithmic parameters are found to be less important and cause less variance in both the far-field waveforms and STFs, meaning algorithmic choices in how we model explosions are less important, which is encouraging for the further use of explosion simulations to study how physical Earth properties affect seismic waveform features and estimated STFs.

Assessment of Change in Rock Mass Permeability in the Vicinity of Underground Explosion from Experimental Data and Numerical Modeling

Assessment of Change in Rock Mass Permeability in the Vicinity of Underground Explosion from Experimental Data and Numerical Modeling

3D Time-Lapse Electrical Resistivity Imaging of Rock Damage Patterns and Gas Flow Paths Resulting from Two Underground Chemical Explosions

Rock damage from underground nuclear explosions (UNEs) has a strong influence on sub-surface gas movement and on seismic waveform characteristics, both of which are used to detect UNEs. Although advanced numerical simulation capabilities exist to predict rock damage patterns and corresponding detection signals, those predictions are dependent on (generally) unknown properties of the host rock. For example, the effects of in-situ mechanical heterogeneities on the explosively generated damage/fractures that provide gas flow pathways to the surface are not well understood, due largely to the difficulty in accessing and characterizing the near-source region. In this paper we demonstrate the emerging use of electrical resistivity tomography (ERT) for imaging rock damage and gas flow patterns resulting from two relatively small-scale underground chemical explosions. Pre-explosion ERT and crosshole seismic imaging revealed a natural fracture zone within the test bed. Post-explosion imaging revealed that the damage zone was non-symmetric and was focused primarily within the pre-existing fracture zone, located 10 m above the first explosion and 5 m above the second explosion. Time-lapse ERT imaging of heated air injected into the detonation borehole revealed the primary gas flow paths to be within the upper margin of the same primary damage zone. These results point to the utility of ERT imaging for understanding rock damage and gas flow patterns under experimental conditions, and to the importance of understanding the effects of geologic heterogeneity on UNE detection signals, particularly gas surface breakthrough times.

On various mechanisms of shear wave generation from underground chemical explosions in hard rocks

SUMMARY Significant shear waves observed during underground explosions can make them look similar to natural earthquakes. In the near field, they can be caused by the source geometry and emplacement conditions, heterogeneous and anisotropic properties of the rock mass, relaxation of a non-uniform in situ stress around the source after the departure of the shock wave as well as by activation of nearby faults. The stress relaxation mechanism is important at depth when the difference in main principal stresses becomes significant. Another mechanism of shear motion generation is due to explosive gas flow from the source cavity into the cracks initiated by the shock wave and joints connected to the cavity. Also, the shock wave from the explosion can cause weakening of the rock either due to permanent damage or shock-induced liquefaction at saturated joints. Numerical modelling of underground chemical explosions in hard rock at various confinement stresses has been conducted to compare various mechanisms of shear wave generation and their seismic characteristics with that of a simple fault rupture process observed during an earthquake.

Proteomic global proteins analysis in blast lung injury reveals the altered characteristics of crucial proteins in response to oxidative stress, oxidation-reduction process and lipid metabolic process

ABSTRACT Background: Blast lung injury (BLI) is the most common fatal blast injury induced by overpressure wave in the events of terrorist attack, gas and underground explosion. Our previous work revealed the characteristics of inflammationrelated key proteins involved in BLI, including those regulating inflammatory response, leukocyte transendothelial migration, phagocytosis, and immune process. However, the molecular characteristics of oxidative-related proteins in BLI ar still lacking. Methods: In this study, protein expression profiling of the blast lungs obtained by tandem mass tag (TMT) spectrometry quantitative proteomics were re-analyzed to identify the characteristics of oxidative-related key proteins. Forty-eight male C57BL/6 mice were randomly divided into six groups: control, 12 h, 24 h, 48 h, 72 h and 1 w after blast exposure. The differential protein expression was identified by bioinformatics analysis and verified by western blotting. Results: The results demonstrated that thoracic blast exposure induced reactive oxygen species generation and lipid peroxidation in the lungs. Analysis of global proteins and oxidative-related proteomes showed that 62, 59, 73, 69, 27 proteins (accounted for 204 distinct proteins) were identified to be associated with oxidative stress at 12 h, 24 h, 48 h, 72 h, and 1 week after blast exposure, respectively. These 204 distinct proteins were mainly enriched in response to oxidative stress, oxidation-reduction process and lipid metabolic process. We also validated these results by western blotting. Conclusions: These findings provided new perspectives on blast-induced oxidative injury in lung, which may potentially benefit the development of future treatment of BLI.

A novel resilience modeling method for community system considering natural gas leakage evolution

With rising natural gas demand, the issue of emergency management of gas leaks in communities is becoming more prominent. Resilience engineering is a successful approach to improving the system's ability in dealing with emergencies. In contrast to natural disasters such as floods and tornadoes, the consequences of a gas leak are closely related to the accident's evolutionary path. However, few reported works have taken the evolution of disasters into account in the assessment of resilience. Conventional methods fail to quantify the public safety performance of a disturbance caused by a natural gas leak. This work presents a novel dynamic approach to assessing resilience that incorporates the evolution of an incident and its interaction with emergency measures. A network structuring model of accident evolution is developed by the Functional Resonance Analysis Method (FRAM) to analyze the potential accident propagation. The explosion consequence of gas leakage escalation is simulated based on Computational Fluid Dynamics (CFD), and the personnel injury criterion is adopted to quantify the temporal and spatial variation characteristics of the system degradation. Then, the dynamic Bayesian network (DBN) is then used to track the interactions between accidents and emergency measures. Taking a real accident case (Shiyan underground gas explosion) as an example, the case study indicates that the proposed method can identify and prioritize emergency measures, as well as provide strong support for decision-making and arrangements in emergency management.

Assessment of gas explosion risk in underground spaces adjacent to a gas pipeline

With the increased number and scale of gas pipelines, gas explosions in underground spaces adjacent to pipelines occur occasionally. A method was proposed in this study for evaluating the explosion risk in underground spaces adjacent to gas pipelines. The method was established on the basis of a full-scale independent underground space (IUS) explosion experiment and the whole-chain accident evolution model of “leak-diffused aggregation-ignition-explosion,” which consists of the possibility, consequence, and correction factors of an underground space explosion was proposed. Explosion possibility assessment included pipeline leakage, diffusion aggregation, and ignition probabilities. In particular, the diffusion aggregation probability assessment method, as the focus here for explosion possibility assessment, was proposed based on the method of micro-elements and behavior of gas diffusion in soil. A manhole explosion experiment was carried out for IUS explosion consequence assessment, including the extent and intensity of explosion flame, overpressure, and debris effects. The experiment also confirmed the conclusion that the explosion overpressure of the manhole was not sufficient to cause harm to people. Flame and fragmentation damage should be paid attention to, especially for an underground space with deep depth(hL ≥ 2 m), large volume, no hinge and light quality manhole cover. The risk assessment method proposed here was applied in H city, and 24,830 underground spaces with high explosion risk were assessed from 510,835 underground spaces. Over the past three years, more than 200 dangerous cases of natural gas leaks and accumulations have been identified.

A laboratory method to simulate seismic waves induced by underground explosions

The seismic waves induced by underground explosions generate geological hazards affecting deep buried tunnels such as rockbursts and engineering-induced earthquakes. This issue is difficult to study through full-scale testing due to the expense and unpredictable danger. To solve this problem, the authors developed experimental apparatus and presented a laboratory method to simulate seismic waves induced by underground explosions. In this apparatus, a combined structure of a diffusive-shaped water capsule and a special-shaped oil capsule was designed. This structure can provide an applied confining stress and freely transmit the stress wave generated by external impact. Therefore, the coupled loading of in situ stress and seismic waves induced by underground explosions in the deep rock mass was simulated. The positive pressure time and peak value of the stress wave could be adjusted by changing the pulse-shaper and the initial impact energy. The obtained stress waves in the experiments correspond to that generated by 0.15–120 kt of TNT equivalent explosion at a scaled distance of 89.9–207.44 m/kt 1/3 .

Evaluation on Underground Refuge Alternatives and Explosion Survivability: a Review

Evaluation on Underground Refuge Alternatives and Explosion Survivability: a Review

Yield estimate for the January 2016 DPRK nuclear test based on InSAR and numerical modelling with mechanical heterogeneity

SUMMARY Interferometric Synthetic Aperture Radar (InSAR) provides a way of measuring ground deformation caused by underground nuclear testing via a satellite remote sensing platform. We present a finite-element model (FEM) of the nuclear test site in the Democratic People's Republic of Korea (DPRK, formerly North Korea) constrained by InSAR data. The model simulates elastic deformation caused by an underground explosion and includes high-resolution topography and mechanical heterogeneity. To the best of our knowledge, we are the first to investigate the effect of mechanical heterogeneity (a layered structure in our case) on deformation modelling at the DPRK test site. Sensitivity testing shows that inclusion of topography, mechanical layering and the combined effect results in 48.2, 22.6 and 91.5 per cent increase in the maximum predicted deformation, respectively. This suggests that previous models that do not account for these complexities may overestimate the nuclear yield and/or underestimate the depth of burial (DoB). We performed a parameter search to solve for the cavity size and DoB that best reproduce ground deformation observed in ALOS-2 InSAR data covering the DPRK's 4th nuclear test (DPRK4). Using these best-fit values with a cavity-yield scaling law, we estimate the yield of DPRK4 to be 10–20 kt at a DoB of 542–826 m. Our method provides an estimate that is independent from and complementary to traditional seismic methods, which is useful for a location that is data-limited.

On the seismic source function of an underwater explosion

SUMMARYThe seismic source function of an underwater explosion (UWE) is studied based on characteristics of the shock wave and the secondary bubble pulses. A mathematic representation for the full pressure history including overpressure and underpressure caused by both shock wave and bubble pulses is presented. Based on the full pressure model, UWEs’ reduced displacement/velocity potentials both in time and frequency domain are obtained. The new seismic source model overcomes the theoretical inconsistency with the UWE seismic source model presented by Savage & Helmberger taking account of the shock wave overpressure only, and the steady-state reduced displacement potential predicted by the full pressure model is much larger than that predicted by the shock wave model by a factor that would exceed 100 for shallow UWEs. Relative seismic effect between underwater and underground explosions is modelled and the result by the full pressure model is consistent with observations that seismic magnitude of an UWE commonly is much larger than magnitude of an underground explosion of the same yield. And to further validate the full pressure model, Pn spectra of a 10 000lbs UWE off the east coast of Florida detonated on 2016 June 10 are modelled for six regional stations, and the results predicted by the full pressure model agree well with corresponding observations.