Subsurface Explosions Research Articles

Deflecting asteroid Itokawa by subsurface explosion: Effect of explosion position on asteroid angular velocity change

Explosion deflection has recently become an important topic in hazardous asteroid deflection. Changes in asteroid velocity and angular velocity, as well as the degree of structural damage, should be fully considered in the explosion deflection scheme. This study investigates the effect of explosion position on the deflection of the asteroid 25143 Itokawa. First, we propose a mathematical model to quickly determine the changes in the angular velocity of Itokawa with explosions at different positions, and verified its reliability through numerical simulations. Mathematical model indicated a maximum 349-fold difference in Itokawa's angular velocity change under explosions at different positions, and revealed that the decisive factor is the force arm (maximum 850-fold difference), not the moment of inertia (maximum 4.01-fold difference). Then, to demonstrate the effect of porosity on shock wave propagation, we established a mesoscopic model based on the porosities of Itokawa's head and body. We used the single-material arbitrary Lagrangian-Eulerian (ALE) and finite element-smoothed particle hydrodynamics (FE-SPH) adaptive methods to simulate the deflection of the asteroid with a 300-kt TNT-equivalent explosion at different positions 10 m underground. The simulated changes in asteroid velocity and angular velocity were consistent with the predictions of the mathematical model. Finally, we investigated the effects of the asteroid geometry and material composition on the shock wave propagation and asteroid damage evolution (material response and structural response).

Cover Picture: Characterization and response of three TNT equivalent materials in subsurface explosions (Prop., Explos., Pyrotech. 10/2023)

Cover Picture: Characterization and response of three TNT equivalent materials in subsurface explosions (Prop., Explos., Pyrotech. 10/2023)

Characterization and response of three TNT equivalent materials in subsurface explosions

AbstractEnergetic compositions utilized for inducing seismic responses are often referred to in terms of their TNT equivalent, a metric which is often misused because observations of interest are not often understood with respect to explosive characteristics. In this investigation, we characterize three energetic compositions used to elicit seismic responses in a highly instrumented testbed to further our understanding of subsurface TNT equivalence. Three different energetic sources are prepared and studied for their fidelity to thermochemically predicted detonation behavior. We present effects of subsurface detonation on subsurface rock and seismic emission as a function of energetic source material within the testbed. Field experiments were conducted using a single thermochemical yield of 5 kg using diverse sources consisting of nitromethane, ammonal, and PBXN‐5 (an HMX based plastic bonded explosive) mixtures at the Energetic Materials Research and Testing Center in Socorro, New Mexico. Relative performance of energy density‐related detonation parameters, such as detonation velocity and pressure, affect the observed response in the subsurface. Most notable, equal thermochemical yields described in terms of TNT equivalence do not correlate to equal thermochemical effects in the subsurface.

Love-type wave propagation in a coated fluid-saturated fractured poro-viscoelastic layer with sliding contacts and point source effect

The present paper studies Love-type wave propagation in a fluid-saturated fractured poro-viscoelastic layer sandwich between a coated elastic layer and a non-homogeneous anisotropic Voigt-type viscoelastic half-space. The interfaces between the layers and the half-space are considered as sliding contacts with two different sliding parameters. An impulsive point source is located at a varying depth in the intermediate poro-viscoelastic layer in the form of the Dirac-delta function. The vertical non-homogeneity in the half-space is assumed to be a combination of linear and exponential functions that vary with depth in the medium. Using the Fourier transforms and Green's functions, the equations of motion, in the form of partial differential equations, are solved analytically. An appropriate boundary condition is used to accomplish this. The closed form of the complex dispersion equation has been obtained by assuming that the wavenumber is in the form of a complex quantity. The validity of our model has been examined using several specific cases and compared to the classical Love wave equation. Numerical and graphical analyses of dispersion and displacement were performed using MATLAB software. It has been found that a single porous medium has a higher Love-type phase velocity than a double porous medium. Additionally, the sliding parameters increase the range of wavenumber when there is no phase velocity. An inverse relationship was found between the depth of the point source and the particle displacement in the coated layer. In addition to contributing to our understanding of geophysical phenomena and subsurface explosions, these findings may provide insight into the inner structure of the planet.

Blast resisting responses and upgrading technology for an underground structure subjected to external explosions

Underground structures are widely constructed as the key parts of lifeline system with synthetic functions in modern society. Simultaneously, the integration of blast-resisting infrastructures and civil underground structures has attracted increasing attention. Therefore, this study investigated the blast-resisting mechanism of underground structures under conditions of surface and subsurface explosion. Then, a series of upgrading approaches for underground structures subjected to external explosion are compared and investigated through the isolation technology, Strain-Hardening Cementitious Composites (SHCC) technology, and partially encased composite structures technology. The obtained results showed that the developed blast-resisting evaluation framework can effectively quantify the multi-performance of the entire underground structure subjected to the external explosions, given the formation of an evaluation database of comparative performances between variant explosion cases to distinguish the component vulnerable to blast locations. Dealing with any possible top-surface explosion and penetrating blast, the proposed isolated column, SHCC column, and partially encased composite column-based methods can effectively protect the vulnerable column, at the same time reducing the dynamic responses near the explosion center. Considering the stochastic property of the explosion, the integration upgrading approach using the SHCC isolated column is suggested for the underground structure subjected to both explosion and earthquake in practice.

Dynamic Response of Underground Tunnel in Soft Soil under Surface and Subsurface Explosion

Dynamic Response of Underground Tunnel in Soft Soil under Surface and Subsurface Explosion

Coseismic Stability Assessment of a Damaged Underground Ammunition Storage Chamber Through Ambient Vibration Recordings and Numerical Modelling

In the past decade, ambient vibration measurements found numerous applications on unstable rock slopes and developed into a powerful tool for site characterization of slope instabilities. In this study, for the first time ambient vibration measurements were applied to a rock mass strongly disturbed and damaged by subsurface explosions. The site above the ammunition storage chamber at Mitholz (Switzerland) is especially interesting because the subsurface geology below the seismic array is well known, including the location of the caverns, and the degree of degradation caused by the subsurface explosions in 1947 of around 40 t TNT of ammunition. Measurement data were analyzed using current state-of-the-art seismic single-station and array methods, focusing on surface-wave dispersion analysis, wave field polarization, wave amplification using site-to-reference spectral ratios and analysis of normal mode behavior. The results allow for calibrating the elastic properties of a 2D numerical rock mechanical model which was used to simulate the stability of the disturbed rock mass during seismic loading. Therefore, ambient vibration measurements can contribute not only to a better understanding of the subsurface, but also for the assessment of earthquake risk.

Modeling Subsurface Explosions Recorded on a Distributed Fiber Optic Sensor

AbstractFiber optic distributed acoustic sensors (DAS) are becoming a widely used tool for seismic sensing. Here we examine recordings of two subsurface chemical explosions, DAG‐1 and DAG‐3, each of which was about one metric ton (TNT equivalent), that were recorded from a helical fiber installed in two boreholes 80 m away from the source location. Several clear phases including the initial P wave, a weak S wave, and a surface reflected P wave are observed on the helical DAS data. We estimate a velocity model using arrival times measured from the fiber. The DAS waveform data were compared with colocated accelerometers at specific depths in both frequency and time domains. The spectra of the DAS data matched spectra estimated from the accelerometer records. Comparisons of observed waveform shape between the accelerometer records and the fiber measurements (strain‐rate) show reasonable agreement except for the data near the event depth. The DAS data and the accelerometer agreed in relative amplitudes but we had difficulties in matching absolute amplitudes, possibly due to errors in metadata. Synthetic strain‐rate waveforms were calculated using a 2D wavenumber algorithm and matched the waveform shape and relative amplitudes. In general, DAS is effective at recording strong ground motions at high spatial density. Comparison of the synthetic seismograms with observed data indicate that the waveforms are not consistent with a pure isotropic explosion source and that the observed S waves originate from very near the source region.

Lateral migration of explosive hazards during maar eruptions constrained from crater shapes

Maar volcanoes are produced by subsurface phreatomagmatic explosions that can move vertically and laterally during an eruption. Constraining the distances that maar-forming explosions move laterally, and the number of relocations common to these eruptions, is vital for informing hazard scenarios and numerical simulations. This study uses 241 intact Quaternary maar crater shapes to establish global trends in size and spacing of explosion position relocations. Maar craters are sorted into shape classes based on the presence of uniquely identifiable combinations of overlapping circular components in their geometry. These components are used to recognize the minimum number of explosion locations responsible for observed crater shapes. Craters with unique solutions are then used to measure the size and spacing of the explosion footprints, the circular area of the largest crater produced by a single explosion of a given energy, that produce the crater shape. Thus, even in the absence of abundant observations of maar-type eruptions, the typical range, size and spacing of explosion positions are derived from maar crater shapes. This analysis indicates that most Quaternary maar eruptions involved at least three different explosion locations spanning distances of 200–600 m that did not always follow the trend of the dike feeding the eruption. Additional evaluation of larger maars, consistent with stratigraphic studies, indicates that centers of explosive activity, and thus the origin of ballistic and density current hazards, can move as many as twenty times during a maar-forming eruption. These results provide the first quantitative constraints on the scale and frequency of lateral migration in maar eruptions and these values can directly contribute to hazard models and eruption event trees in advance of future maar-type eruptions.

Dynamic performance prediction and influencing factors analysis of buried polyethylene pipelines under subsurface localized explosion

Although polyethylene (PE) pipelines have been extensively used in engineering fields, very little effort has been devoted to their abilities against blast loads. In the present study, numerical method is used to predict the dynamic performance of buried small-diameter PE pipelines under subsurface localized explosion. The effectiveness of a numerical model was firstly evaluated to entirely replicate the experimental damage process of PE pipelines. Then, parametric studies are performed to show the dynamic response of PE pipelines under subsurface localized explosion. Finally, the main influencing factors are analyzed according to the grey system theory. The results show that the front and back faces, top and bottom of the pipelines, where facing explosive charge are the main failure positions of PE pipelines due to the local effect of blast load. The peak pressure, resultant displacement, peak effective strains, and peak vibration velocities of the PE pipelines increase with the explosive mass increasing. The peak pressures and peak vibration velocities decrease with the pipe size decreasing. Reducing the pipe size could increase the maximum effective strain of the pipe facing the explosive center, and reduce the vibration velocity of the pipe near the explosive center. The change law of peak pressure of PE pipelines caused by changing explosive mass and pipe size is different from that of peak vibration velocity of PE pipelines. As a sequence, the three influencing factors (explosive mass, pipe size and blasting distance) should also be considered to analyze the influence of subsurface explosion on the buried small-diameter PE pipelines.

The effect of GFRP on reinforcing the buried and internally pressurized steel pipes against terrorist attacks

In recent years, the occurrence of numerous intentional and accidental explosions in buried pipelines, especially in oil and gas pipelines, has been turned to a proper subject of research. The present research, for the first time, studies the utilization of GFRP for reducing the deformation of buried and internally pressurized steel pipes against explosions through the non-linear three-dimensional finite element method. The Combined Eulerian-Lagrangian (CEL) algorithm is used for modeling simulation. It means that the pipe and GFRP are modeled using the Lagrangian algorithm and air, soil and explosives are modeled using the Eulerian algorithm. The studied pipe is API-X65 with an outside diameter of 914.4 mm and the burial depth of 2.5 m. The explosive material is TNT with 10 kg of weight and in the 1 m height below the ground. The results of the model were compared to the results of field tests and the experimental equations presented by previous researchers, and good compatibility was observed. Utilization of GFRP decreases maximum equivalent strain, transverse deformation, longitudinal strain and explosion energy imposed on the pressurized pipeline for about 35.3, 29.6, 13 and 63%; respectively. The internally pressurized pipeline of API-X65 with the wall thickness of 15.88 mm and with the GFRP reinforcement with 7 mm of thickness has acceptable resistance against explosion, in a way that transverse deformation of it is in the acceptable limit and its longitudinal strain is lower than the yield strain. Using the results of this research, we can protect the under-construction or operation buried pipelines against the sub-surface explosions.

Mechanical Damage and Response of a Buried Steel Pipeline Under Subsurface Explosion Load

Abstract Subsurface explosions seriously threaten the safety and reliability of buried oil and gas pipeline. In order to investigate the mechanical responses of buried steel pipeline under subsurface explosion load, a numerical model of pipeline–soil coupling under explosion load was developed. Stress, displacement, plastic deformation, and local buckling of the buried pipeline were investigated. The effects of trinitrotoluene (TNT) magnitude, pipeline diameter-thickness ratio, pipeline's buried depth, explosive depth, and explosive offset on the mechanical response of pipeline were studied. The results show that the response time of buried pipeline is very short under the explosion load. There is a dent appearing on the pipeline section toward the exploding location. Cross-sectional area of the pipeline decreases along the time during the explosion, but it gradually increases for the elastic recovery. Pipeline's deformation and total energy increase gradually with the increasing of trinitrotoluene magnitude or diameter-thickness ratio, but they decrease with the increasing of the buried depth or explosive offset. With the explosive depth increases, the pipeline's plastic deformation first increases and then decreases. The pipeline's energy curve can be used to determine the buckling state under explosion load. The empirical formulas of the maximum strain and dent rate for buried pipelines have been obtained and can be used for the pipeline safety assessment.

Explosions recorded underwater offshore of southern California

Sounds from explosions can travel long distances underwater due to their high sound pressure levels, potentially impacting marine life. We evaluated and characterized explosion sounds from underwater recordings to better understand the signature of these sounds, how they propagate in the ocean, and how they may be differentiated for different source types. A controlled experiment using small (∼2 g) “seal bomb” sources at various source-receiver ranges was conducted offshore of southern California to characterize their waveform signature, including bubble pulses due to subsurface explosions ∼4 m depth and peak source level estimate of 234 dB re 1 µPa at 1 m. Opportunistic recordings of missile explosions during military exercises offshore of southern California were made by autonomous hydrophone recorders ∼1000 m deep. The military explosions were presumably at or near the sea surface and did not exhibit bubble pulses, allowing them to be differentiated from fisheries seal bomb sources for manual or automatic signal classification in underwater acoustic recordings.

Insights into the dynamics of mafic magmatic-hydromagmatic eruptions from volatile degassing behaviour: The Hverfjall Fires, Iceland

The style and intensity of hydromagmatic activity is governed by a complex interplay between the relative volumes of magma and water that interact, their relative viscosities, the depth of subsurface explosions, the substrate properties, and the vent geometry. Fundamental questions remain, however, regarding the role of magmatic vesiculation in determining the dynamics of magma-water interaction (MWI). Petrological reconstructions of magmatic degassing histories are commonly employed to interpret the pre- and syn-eruptive conditions during ‘dry’ magmatic eruptions, but the application of similar techniques to hydromagmatic activity has not yet been fully explored. In this study, we integrate glass volatile measurements (S, Cl, H2O and CO2) with field observations and microtextural measurements to examine the relationship between degassing and eruptive style during the Hverfjall Fires fissure eruption, Iceland. Here, coeval fissure vents produced both ‘dry’ magmatic (Jarðbaðshólar scoria cone complex) and variably wet hydromagmatic (Hverfjall tuff ring) activity, generating physically distinct pyroclastic deposits with contrasting volatile signatures. Matrix glass volatile concentrations in hydromagmatic ash (883 ± 172 [1σ] ppm S; 0.45 ± 0.03 [1σ] wt% H2O; ≤20 ppm CO2) are consistently elevated relative to magmatic ash and scoria lapilli (418 ± 93 [1σ] ppm S; 0.12 ± 0.48 [1σ] wt% H2O; CO2 below detection) and overlap with the range for co-erupted phenocryst-hosted melt inclusions (1522 ± 127 [1σ] ppm S; 165 ± 27 [1σ] ppm Cl). Measurements of hydromagmatic glasses indicate that the magma has degassed between 17 and 70% of its initial sulfur prior to premature quenching at variably elevated confining pressures.By comparing volatile saturation pressures for both magmatic and hydromagmatic glasses, and how these vary through the eruptive stratigraphy, we place constraints on the conditions of MWI. Crucially, our data demonstrate that the magma was already vesiculating when it encountered groundwater at depths of 100–200 m, and that the external water supply was sufficient to maintain MWI throughout the eruption with no significant vertical or lateral migration of the fragmentation surface. We propose that development of an in-vent water-sediment slurry provides a mechanism through which the elevated confining pressures of ~1.6–2.6 MPa (or up to 6 MPa accounting for uncertainty in CO2 below analytical detection) could be maintained and buffered throughout the eruption, whilst enabling vertical mixing and ejection of fragmented juvenile and lithic material from a range of depths. Importantly, these results demonstrate that the volatile contents of hydromagmatic deposits provide valuable records of (1) the environment of MWI (e.g., groundwater versus surface water, vertical migration of the fragmentation level) and (2) the state of the magma at the time of fragmentation and quenching. We further suggest that the volatile content of tephra glasses provides a reliable alternative (or additional) indicator of a hydromagmatic origin, particularly for reduced Ocean Island Basalts where late-stage volatile saturation and degassing (S, H2O) occurs over a pressure range relevant to typical MWI environments.

Trends in maar crater size and shape using the global Maar Volcano Location and Shape (MaarVLS) database

A maar crater is the top of a much larger subsurface diatreme structure produced by phreatomagmatic explosions and the size and shape of the crater reflects the growth history of that structure during an eruption. Recent experimental and geophysical research has shown that crater complexity can reflect subsurface complexity. Morphometry provides a means of characterizing a global population of maar craters in order to establish the typical size and shape of features. A global database of Quaternary maar crater planform morphometry indicates that maar craters are typically not circular and frequently have compound shapes resembling overlapping circles. Maar craters occur in volcanic fields that contain both small volume and complex volcanoes. The global perspective provided by the database shows that maars are common in many volcanic and tectonic settings producing a similar diversity of size and shape within and between volcanic fields. A few exceptional populations of maars were revealed by the database, highlighting directions of future research to improve our understanding on the geometry and spacing of subsurface explosions that produce maars. These outlying populations, such as anomalously large craters (>3000m), chains of maars, and volcanic fields composed of mostly maar craters each represent a small portion of the database, but provide opportunities to reinvestigate fundamental questions on maar formation. Maar crater morphometry can be integrated with structural, hydrological studies to investigate lateral migration of phreatomagmatic explosion location in the subsurface. A comprehensive database of intact maar morphometry is also beneficial for the hunt for maar-diatremes on other planets.

Mechanism and structure of subsurface explosions in granular media

Subsurface explosions for ejecting low-density regolith from the surface of asteroids and comets are studied by solving two sets of coupled Euler equations. Formation and propagation of a granular shock is explored. The granular-shock radius exhibits a power-law relation with explosion time.

Updates to Concepts on Phreatomagmatic Maar-Diatremes and Their Pyroclastic Deposits

Recent work is changing our understanding of phreatomagmatic maar-diatreme eruptions and resulting deposits. In previous models, explosions were often inferred to take place only at the base of a diatreme, with progressive downward migration due to a cone of depression in the host aquifer. However, diatremes themselves contain much water that is heterogeneously distributed, and field evidence supports the existence of explosion sites at many vertical and lateral locations within them. Crater sizes have been used to estimate explosion energies, but this only works for single-explosion craters where the depth of explosion is independently known, and has limited value for multi-explosion maar-diatremes. Deep-seated lithic clasts in tephra ring beds have been taken to indicate the depth of the explosion that produced that bed. However, only relatively shallow explosions actually vent to the surface, and deep-seated lithics are gradually brought to shallow depths through step-wise mixing of multiple subsurface explosions. Grain-size of tephra-ring deposits is often inferred to indicate fragmentation efficiency. However, other factors strongly influence deposit grain size, including the scaled depth of an explosion and the interaction of an erupting jet with topography around a vent (e.g., crater), along with long recognized effects of mechanical properties of host rocks and recycling within the vent/diatreme. These insights provide a foundation for future research into this important volcano type.

Diatreme evolution during the phreatomagmatic eruption of the Songaksan tuff ring, Jeju Island, Korea

The Songaksan tuff ring, Jeju Island, Korea, which erupted ca. 3.7 ka BP in a coastal setting, provides an unusual opportunity to study the processes of phreatomagmatic eruption and the formation of a diatreme because of the exceptionally well-preserved ejecta beds and well-known subsurface geology. The tuff sequence can be divided into four units (A to D), which have distinctly different accidental componentry (quartz-rich vs. quartz-poor), grain surface features (abraded and ash-coated vs. unabraded and uncoated), and chemical compositions of juvenile particles. The basal tephra bed of unit A, which probably erupted after the removal of the relatively hard shallow-level ( 120 m deep) accidental grains, suggesting that the early erupted tephra had not yet experienced recycling and pre-eruption mixing in the diatreme. On the other hand, the overlying tephra beds of units A, B, and D contain an abundance of abraded and ash-coated juvenile/accidental grains, suggesting that the tephra comprised significant proportions of “recycled” or “premixed” materials from previous eruptions or subsurface explosions, which participated in the explosion-driven mixing in the diatreme before eventual ejection from the diatreme. Unit C is unusual in that it comprises extremely rare accidental grains and ash-coated juvenile/accidental grains. We interpret that the supply of solid materials, either accidental or juvenile, to the diatreme was greatly reduced because of temporary stabilization of the diatreme and the reduction in magma flux to the diatreme. The diatreme is therefore envisaged to have been filled with a water-saturated slurry, in which particle abrasion and adhesion were inhibited. We also infer that the diatreme fill was temporarily removed by a powerful explosion before eruption of unit C on the basis of the near absence of the tephra grains from earlier eruptions throughout the tephra beds of unit C. The ratio of tachylite to sideromelane grains generally increases up-section of the tuff sequence with two abrupt drops across the tuff unit boundaries. These variations are coincident with the changes in the chemical composition of juvenile particles, suggesting an overall decrease in magma flux punctuated by brief increases in magma flux associated with the arrival of new magma batches. The textural and compositional variations of the Songaksan tuff ring suggest that there can be significant variability in diatreme processes even during a purely phreatomagmatic eruption of a tuff ring, including removal and renewal of the diatreme fill, and that there is still much room for further investigation of the diatreme processes from the ejecta beds in order to make the current diatreme model more robust.

Recycling in debris-filled volcanic vents

Abstract Eruptions through debris-filled vents produce deposits containing magmatic juvenile lithic and recycled clasts. Recycled clasts are exposed to multiple transportation and fragmentation events. We used experiments with multiple subsurface explosions to track clasts and highlight dominant recycling processes in eruptions through analog debris-filled vents. Recycled clasts include those that fall back into and reside in the vent for extended time periods and those that return to the vent through crater growth or collapse. Clasts are recycled by any combination of lofting and fallback of material in the crater by explosion jets, mixing and churning of material at depth in the debris fill, and redistribution of extra-crater deposits by explosion-induced excavation or slumping. We compare experimental processes with natural deposits that preserve recycling signatures from discrete explosions through debris-filled vents such as maar-diatremes, Strombolian vents, and hydrothermal craters. Clasts may not preserve textures diagnostic of their complete recycling histories, but can be used to infer if that history occurred in part in the vent debris or in the eruptive jet. Experiment results and natural deposits suggest that for volcanic craters that undergo multiple explosions, clasts likely undergo some form of recycling before final deposition outside the craters. The underestimation of recycled clast contributions to deposits can lead to inaccurate estimates of thermal budgets and eruption processes.

The application of CFRP to strengthen buried steel pipelines against subsurface explosion

Multiple explosions in the route of oil and gas transmission pipelines during recent years demonstrate that terrorist attacks and sabotages have unfortunately increased. The present investigation is carried out numerically in order to minimize the amount of damages imposed on steel pipelines under close-in explosions. This research presents a novel concept, using CFRP (Carbon Fiber Reinforced Polymer) to strengthen the wall of steel pipelines against these incidents. For this purpose, a full coupled 3D finite element model developed using a combined Eulerian-Lagrangian method. The simplified Johnson-Cook material model, the JWL equation of state, and the ideal gas equation of state were employed for modeling the pipe material behavior, charge detonation, and air, respectively. Mechanical behavior of the composite wrap was simulated using an anisotropic material model and the damage initiation criteria were based on Hashin's theory. In addition, soil mass behavior was modeled applying a Drucker-Prager strength criterion with piecewise hardening and hydro tensile limit accompanied by Mie-Grüneisen equation of state. Several comparisons carried out between the results from present investigation and those from field and empirical studies and good agreements were observed. The results show that using a proper thickness of CFRP wrap for every particular circumstance can significantly improve the performance of steel pipelines under blast loads. For instance, in the current example, maximum equivalent strains developed in the most of the studied pipelines decreased by over 30% (up to 64%) with the application of 4-mm-thickness CFRP wrap. The present study contributes to protective design of steel pipelines.