Ground Shock Research Articles

Study on the safe distance of spatial intersecting tunnel cavern under ground shock

The vertical distance of intersection area is an important factor dominating the service performance of spatial intersecting cavern. To obtain the influence of vertical distance on the dynamic response of orthogonal spatial intersecting caverns under ground shock, the plastic region and peak particle velocity (PPV) distribution are investigated by numerical simulation. A finite-dynamic model is established to simulate the mechanical response of the deeply bureid structure subjected to coupled static and dynamic load, with an artifical boundary condition setting method. The results indicate that as the vertical distance decreases, the plastic region in the intersection area gradually merges, while the bolt support at the lower cavern vault effectively suppresses the destruction of the intersection area. The free surface of the lower cavern vault weakens the bottom support conditions of the upper cavern floor structure, resulting in higher PPV when vertical distance is smaller. Conversely, as vertical distance increases, isolation effect of upper cavern on ground shock weakens, leading to an increase and followed by a decrease in PPV at the lower cavern vault and straight wall. Morever, when vertical distance exceeds than 3 times the cavern characteristic size, the lower cavern exhibits dynamic response characteristics of deeply buried single-cavern. when vertical distance within 3 times, there is significant interaction between caverns with inverse relationship between dynamic axial stress on bolts in intersection area and PPV at lower cavern vault. It is recommended to use comprehensive criteria involving PPV and plastic region distribution to evaluate safety performance for spatial intersecting cavern.

Research on the Shock Wave Overpressure Peak Measurement Method Based on Equilateral Ternary Array.

The measurement process of ground shock wave overpressure is influenced by complex field conditions, leading to notable errors in peak measurements. This study introduces a novel pressure measurement model that utilizes the Rankine-Hugoniot relation and an equilateral ternary array. The research delves into examining the influence of three key parameters (array size, shock wave incidence angle, and velocity) on the precision of pressure measurement through detailed simulations. The accuracy is compared with that of a dual-sensor array under the same conditions. Static explosion tests were conducted using bare charges of 0.3 kg and 3 kg TNT to verify the numerical simulation results. The findings indicate that the equilateral ternary array shock wave pressure measurement method demonstrates a strong anti-interference capability. It effectively reduces the peak overpressure error measured directly by the shock wave pressure sensor from 17.73% to 1.25% in the test environment. Furthermore, this method allows for velocity-based measurement of shock wave overpressure peaks in all propagation direction, with a maximum measurement error of 3.59% for shock wave overpressure peaks ≤ 9.08 MPa.

Ground deformation and blast wave propagation in dry sand subjected to buried explosion: A centrifuge modelling study

A series of centrifuge model tests of buried explosions in dry sand were designed and performed to investigate the blast effects in diverse underground explosion (UE) scenarios. The typical ground deformation pattern and blast wave propagation in different types of UE events were modelled. The excavated cratering was observed in shallow-buried excavation explosion tests. Surface collapse and subsidence craters were formed in the partially contained explosion tests, in which the initial ground motion direction turned from upward to downward with the increase of burial depth. The scaling law for centrifuge modelling of blast wave propagation was derived and examined. The critical burial depth for complete coupling of ground shock energy is within the range of 0.4 m/kg1/3 and 0.8 m/kg1/3, and the gravity effect on blast wave propagation can be disregarded under centrifugal accelerations of 62 g and 106 g (g is the Earth's gravity). The elastic blast wave velocity in dry sand was determined in the model test, and it increased with the burial depth. The attenuation laws for peak pressure and peak scaled acceleration in dry sand were calibrated, and the scaling coefficient for peak pressure estimation increased with the medium's acoustic impedance, while the attenuation coefficient showed a contrasting trend.

Experimental and numerical study on explosion cratering and coupled ground shock in clay

The ground shock induced by underground explosion poses a serious threat to underground projects. Currently, a unified calculation method for ground shock effects coupled with cratering effect has not been established owing to limited test data. This study adopted the ground shock effective crater volume as the energy source of the underground explosion. An equivalent calculation method for ground shock effects in cratering explosion was proposed. A theoretical conversion method between the three the coupling coefficient of equivalent yield, the coupling coefficient of ground shock energy, and the coupling coefficient of ground shock parameter has been developed. Through explosion simulation tests with varying burial depths in clay media, the changing patterns between the size of visible craters, ground shock effective craters and coupled ground shock energy were revealed. A numerical calculation model was established to investigate the relationship between the ground shock effective crater size and energy coupling of the ground shock in detail. By comparing and analyzing the theoretical, experimental, and numerical simulation results, the relationship between the explosive coupling coefficient of ground shock energy and the scaled depth of burial (SDOB) of clay was presented. The research results indicated that there was a linear relationship between the underground explosion compression crater volume (or fragmentation zone volume) and the ground shock energy. The test and numerical simulation analysis results validated the correctness of the coupling coefficient of ground shock conversion calculation method. The obtained clay coupling coefficient of equivalent yield function expression can accurately and rapidly predict the ground shock effect of underground explosions, providing a calculation basis for the anti-explosion design of underground engineering under clay geological conditions.

Ground shock attenuation performances of wire-rope-based meta-isolators

In this research, two types of novel meta-isolators were designed based on traditional wire-rope isolators and made by embedding mass-spring resonators into the wire-rope isolator. Measurement methods to reveal attenuation abilities of these meta-isolators were suggested through quasi-static cyclic loading tests, shaking table tests, and in-field explosion experiments. In the quasi-static tests, meta-isolators have greater hysteresis area under the same excitation displacement, which represents much greater energy consumption. Using shaking table tests and measurement, the vibration attenuation ability of the meta-isolators is improved in the designed resonant frequency, and the response amplitudes are significantly reduced compared with the conventional wire-rope isolators. Blast-induced ground shock experiments reveal that the meta-isolators indeed have an advantage over the conventional isolators in the aspect of shock resistance and the attenuation efficiency exceeds 98 %, providing a new idea and reference for protective engineering.

Blast wave attenuation of nonlinear meta-isolation system: Theoretical analysis and experimental validation

In the field of protective engineering, wire rope isolators are usually applied in the isolation floor to mitigate the impact and vibration induced by explosive blast. In this paper, two kinds of meta-isolation systems were proposed and designed based on the local resonance, and investigated by means of theoretical analysis, numerical calculation and experimental research. First, the force-displacement hysteresis loops of the selected wire rope isolators are obtained by the cyclic loading tests, and identified by a mathematical model to make preparations for numerical calculation. Then, in order to discuss the influence of mass ratio, stiffness ratio and damping ratio on the shock isolation, the two-degree-of-freedom (TDOF) linear and nonlinear models are studied based on the mode superposition method and fourth-order Rugga-Kutta method respectively. Finally, the blast-induced ground shock experiments were conducted to evaluate the isolation efficiencies of conventional isolation systems and meta-isolation systems. The experiment results reveal that the isolation efficiency of meta-isolation system can increase by 10% points vertically and 16% points horizontally compared to conventional systems, which indicates that the meta-isolation system has great potential to be adopted in the engineering structures and provides a new idea and reference for protective engineering.

Dynamic Response Analysis of Segmental Lining under Ground Shock: A Simplified Calculation Method

The tunnel lining segments are assumed to be rigid, and the tensile, compression, shear, and bending properties of the joints are considered. A simplified calculation method for the dynamic response of the structure under the ground shock is proposed, and its correctness is verified by comparing it with results from the finite element method. Using this method, the dynamic response of a subway tunnel lining is calculated, the change in joint force is studied, and the influence of the angle between the load and the center of the minimum segment and the wavelength–diameter ratio on the peak joint force is examined. The results indicate that under the ground shock, shallow tunnel lining is in the impulsive regime, and the force of segment joints is mainly compressed. As the wavelength–diameter ratio increases, the peak values of the lining top displacement and vertical deformation increase significantly, and the proportion of displacement and deformation caused by the inertial force gradually decreases. Sine and cosine functions can be used to preliminarily judge if the bending moment and radial force of the joint are too large or too small, so that the resistance of the lining to ground shock can be improved to a certain extent by setting the positions of lining joints reasonably.

Experimental and numerical study on ground shock propagation in calcareous sand

Surface explosion tests were conducted on calcareous sands to study the ground shock propagation in this medium. In the tests, ground shock at scaled distances between 0.33 m/kg1/3 and 1.46 m/kg1/3 was measured. After each explosion, the surface craters were observed and measured. The propagation and attenuation law of the peak pressure was derived according to the experimental measurement. The shock wave velocity and rise time were derived based on the pressure time-history curves. The empirical formula for pressure time-history curve of direct ground shock in calcareous sand induced by surface explosion was derived, and the predicted impulses showed good agreement with the experimental impulses. The indirect ground shock induced by air shock compression effect on the soil was discussed. Based on the field blast test results, validated numerical models were established to investigate the propagation of direct and indirect ground shock in calcareous sand. The attenuation law of peak pressure of indirect ground shock was then derived according to the numerical simulation results. Besides the surface explosion scenario, the contained burst cases were also modelled. The critical scaled depth of burial was derived as 1.3 m/kg1/3 in calcareous sand based on the surface crater and shock impulse.

Enhancement of explosive effect of thermobaric explosive by metal reactive material

AbstractReactive materials have mechanical properties comparable to metal materials and also have the reaction‐release energy characteristics of energetic materials. The calorific value of reactive materials is even higher than that of explosives. They can react under high pressure/high temperature and release a large amount of chemical energy. Therefore, reactive materials have a wide range of potential applications in aviation and national defense fields. This study examines the energy release characteristics of the metal reactive material casing (MRMC) under thermobaric explosives and compares them to traditional steel casing. The test specimens had the same casing‐charge mass ratio and size, with the only difference being the casing material: reactive material (with reactive elements Zr and Al) and AISI 1020 steel. The physical and chemical properties of the reactive materials were tested and analyzed using ICP‐MS, oxygen bomb calorimeter, and SHPB. Through explosion tests, the characteristic parameters of explosion fireball and ground shock wave overpressure were measured. And the reactive fragments recovered from the experiment were subjected to XRD testing. The results show that MRMC can significantly increase the diameter, duration, and temperature of the explosion fireball compared to steel casing data. The maximum fireball diameter of the MRMC specimen increased by 31.9 %, while the duration before attenuation increased by 47.3 %. MRMC can increase the area ratio of high‐temperature areas (greater than 1300 °C) in the fireball. MRMC increases the overall temperature of the fireball, not just in specific local areas. Additionally, MRMC significantly enhances far‐field shock waves. At a scaled distance of 2.54, the peak overpressure and positive impulse of the MRMC specimen were 50 % and 52 % higher than those of the steel specimen, respectively. This study provides new insights into the application, design, and energy release research of MRMC.

Wave structuring viscosity in the shock compaction of solid matter

The response of geologic matter to large scale impact or explosion is dependent on the time history of the encompassing shock wave. The kinetics of localized physical and chemical transitions brought about by the shock wave are responsive to this time history. Solid state viscosity of the media is responsible for establishing the time history of a shock wave. Melosh [2003] recognized need for the understanding of viscosity on the petrologic and lithologic scale, and accordingly, undertook the assessment and analysis of available nuclear ground shock measurements. Fundamental observations were achieved. The present report furthers the epic efforts of Melosh. Pursuing both the nuclear ground shock data and supporting laboratory test data, methods for, and calculations of, the viscosity of solid materials on the respective scales are undertaken. Recognition of the applicability of viscoelasticity in modelling the shock response is demonstrated and applied. The report closes with discussion of universal features of the shock wave viscous time-history in solid materials. Solid viscosity as an adiabatic invariant is posed and commonalties are noted of the solid shock wave with the nonlinear dynamics of ocean waves.

A practical method for predicting and analyzing the consequences of ammonium nitrate explosion accidents adjacent to densely populated areas

Several catastrophic ammonium nitrate (AN) explosion accidents have been reported during the last decades. Previous studies have been mainly focused on investigating adverse effects caused by the AN explosion, while only a few systematically analyzed the consequences and impacts of AN explosions. This study collects data from three typical AN explosions (accidental explosion of the US fertilizer plant in 2013; an accidental explosion of China's Tianjin port in 2015, and a recent explosion (2020) of the Beirut port in Lebanon). The consequences of accidental explosions were analyzed by mathematical equations that further provide scientific explanations for AN explosions. Based on the explosives' properties on-site, these accidental explosions were caused by condensed phase explosives. Comparison with the conditions at the explosion site indicated that blast overpressure was the primary factor in the loss of life and damage to the building, while ground shock was a secondary factor. The severity of loss of life and building damage from explosions decreased with increasing distance. These distances could be calculated by the scaling law, which was replaced by the equivalent TNT mass of the explosive and the damage scale's overpressure boundary value. In addition, mapping the damaged area on a map helped in the visual presentation of the consequence assessment. The long-term environmental and ecological impact due to the explosions was also an important issue that could not be ignored. Overall, this study establishes a simple and easy-to-use method to rapidly predict and assess the consequences of an explosion, and provides technical guidance for future emergency response to similar large-scale accidents.

On the dynamic response of rectangular liquid storage structure subjected to blast-induced ground shock

The paper aims to investigate the dynamic response of the rectangular liquid storage structure (LSS) under blast-induced ground shock. A two-way fluid–structure interaction (FSI) finite-element model was established, and its effectiveness was verified using a laboratory experiment conducted on an explosion shock and vibration simulation platform (ESVSP). The relationship between the mode shape and frequency was explored using modal analysis. Higher-order modes are characterised by more half-waves preferentially forming in the short sidewall and adjacent sidewalls vibrating in the same direction. The sensitivities of the deflection, hydrodynamic pressure, and equivalent strain in relation to the peak, duration, and loading direction of ground acceleration (i.e. PGA, TGA, and DGA) were highlighted. The results showed that the LSS response magnitude increases linearly as the PGA increases, whereas it first increases and then decreases as the TGA is extended. Furthermore, a feasible method for building a standard shock response spectrum (SRS) was proposed, in which the ground-shock effects were divided into mitigation, enhancement, and equality regions. It is beneficial to evaluate the extreme value of the LSS response to ground shock. The LSS vibration is dominated by different modes as the DGA is varied. The deformation mechanism was revealed by considering the boundary conditions and force characteristics. The conclusion indicates that the bottom middle of the sidewall, as a weak link, needs to be protected.

Numerical simulation of buried steel pipelines subjected to ground surface blast loading

Steel gas pipelines are important component in energy sector. Due to its easy accessibility and importance, shallow-buried pipelines are becoming targets of intentional attack. Therefore, it is urgent to investigate the failure mechanism of buried pipelines subjected to ground surface blast loadings and carry out quantitative damage assessment of pipelines. The present study performs numerical simulation on the resistance of buried pipelines subjected to ground surface explosion. The simulated ground shock propagation in the soil medium was validated with technical manual TM5-855-1 as well as experimental data. The effects of charge weight, stand-off distance, explosive position offset, pipe diameter, pipe wall thickness, buried depth, and steel grade as well as different soil types were investigated. It was found that for the grade X70 pipe with the same buried depth 760 mm, the cross-sectional flattening ratio under charge weight 227 kg (typical sedan bomb) was nearly 544 times greater than the case in 2.3 kg charge weight (typical pipe bomb). The flattening ratio decreased 99.9% because of the buried depth increased from 300 mm to 1800 mm. The decrease in pipe diameter from 860 mm to 350 mm caused 89.6% reduction in flattening ratio. The increase in wall thickness from 4.80 mm to 12.7 mm caused 99.7% decline in flattening ratio. Similarly, it showed the flattening ratio decreased 29.3% when the steel grade increased from X42 (yield strength 290 MPa) to X80 (yield strength 580 MPa). The blast resistance was the worst when the pipeline was buried in clay soil, in which the flattening ratio was 74.8% and 40.3% greater as compared with sandy loam and soil medium. An analytical formula was derived to predict the flattening ratio of pipelines against surface explosion.

Study on the ground impact vibration intensity model of high energy warhead explosion

Introduction: In the warhead explosion process, the ground impact vibration intensity will directly affect the target buildings and instruments safety, and it is also of great significance to accurately evaluate the ammunition explosion damage power.Methods: In this study, the finite element numerical simulation method was used to analyze the explosion shock wave pressure and ground shock vibration velocity of TNT explosive with a mass of 100 kg∼1000 kg, and the ground transmission medium of sandy soil, C35 and C140 concrete, and the shock wave pressure and ground shock vibration velocity propagation and distribution law was clarified. Based on the explosion similarity law and dimensional analysis method, a ground impact vibration velocity theoretical calculation model with clear physical significance is established by introducing the property ground propagation medium parameters, taking into account the factors affecting the ground impact vibration velocity.Results: The model calculation accuracy is verified by the measured data. The verification results show that the model calculation accuracy is higher than 91.8%, which improves the calculation accuracy of the explosion site ground impact vibration velocity.Discussion: This research provides more accurate and scientific theory and data support for the ammunition explosion damage power evaluation, and provides a reference for the shock and vibration resistance performance design of instruments, equipment and buildings. It has strong engineering application value.

A geotechnical seismic isolation system based on marine sand cushion for attenuating ground shock effect: Experimental investigation

In this paper, an experimental study is introduced on the feasibility of applying a geotechnical seismic isolation system based on marine sand cushion (GSI-MSC) to resist explosion-induced ground shocks. The isolation system is characterised by low cost, easy availability, and slippage limitations, and it is particularly suitable in the protection of engineering structures during emergencies. Laboratory experiments on a steel tank structure were performed using a self-developed explosion shock and vibration simulation platform. The attenuation effects of the isolation system on ground motion, superstructural vibration and structural deformation were analysed. The results showed that GSI-MSC can reduce the intensity of ground shock, decrease the amplification effect of structural vibration, and weaken structural deformation. The attenuation effects were significantly enhanced with an increase in sand cushion thickness. The isolation mechanism was revealed from the perspective of spectrum analysis. The decreased lateral stiffness and reduced damping ratio improved the soft layer effect and internal energy dissipation of the sand cushion. This in turn led the GSI-MSC to exhibit a better harmonic attenuation effect over a wider range of high frequencies, beginning at a lower threshold. After isolation, the principal frequency of the ground motion decreased while the amplitude of high-frequency harmonics decreased, resulting in the weakening of the superstructural dynamic response. This indicated that the isolation system has a more stable attenuation effect on the low-period structures.

Event-Triggered Sliding Mode Impulsive Control for Lower Limb Rehabilitation Exoskeleton Robot Gait Tracking

Lower limb rehabilitation exoskeleton robots (LLRERs) play an important role in lower limb rehabilitation training and assistance walking for patients with lower limb movement disorders. In order to reduce and eliminate adverse effects on the accuracy of human motion gait tracking during walking with an LLRER, which is caused by the gravity and friction, the periodic ground shock force, and the human–exoskeleton interaction force, this paper proposes a feedforward–feedback hybrid control strategy of sliding mode impulsive control with gravity and friction compensation, based on the event-triggered mechanism of Lyapunov function. Firstly, to realize high-precision gait tracking with bounded error, some constraints on controller parameters are deduced by analyzing the Lyapunov-based stability. Secondly, the Zeno behavior of impulsive event triggers is excluded by the analysis of three different cases of the triggering time sequence. Finally, the effectiveness of the proposed hybrid controller is verified by the numerical simulation of the LLRER human–exoskeleton integrated system based on a three-link simplified model. It shows that an event-triggered sliding mode impulsive control strategy with gravity and friction compensation can achieve complete gait tracking with bounded error and has excellent dynamic performance under the constraints.

Determination of Blast Impact Range and Safe Distance for a Reinforced Concrete Pile Under Blast Loading

Piles transfer structural loads to the hard layers of the soil or rock; thus, any damage to the pile foundations could have irreparable consequences. A surface blast can create a ground shock that transmits the blast energy along the surface and at depths. Explosion research necessitates technical design to mitigate the adverse effects on nearby structures and facilities. The blast impact range and the safe distance at which the pile will avoid structural damage are two critical parameters for the design of a pile under blast loading. Therefore, this study used the coupled Eulerian-Lagrangian method to determine the blast impact range and safe distance for reinforced concrete piles (RC piles) subjected to blast loading. The results for clayey and sandy soils revealed that an increase in the explosive depth had no significant effect on the safe distance, despite a decrease in the compressive and tensile damage to the pile. Increasing the mass and depth of the blast decreased the ultimate compressive bearing capacity of the pile and increased the blast impact range. Sandy soil performed better than clayey soil against blast loading. The findings of this study can be applied to various projects, including critical structures near gas transmission lines or vulnerable to terrorist attacks.

A theoretical modelling study on deep buried pipelines subjected to blast-induced ground shock

A theoretical modelling study on deep buried pipelines subjected to blast-induced ground shock

Blast Resistance Capacity of Seismically Designed Building Frames

Because of the inherent uncertainty in the blast loading caused due to terrorist attacks, most buildings are not designed for blast loading, but they are routinely designed for earthquake demand. If the blast resistance capacity of the seismically designed building can be evaluated, the risk of the blast loading caused due to the terrorist attacks can be reduced by upgrading the seismic design of the building. With this background in view, the present paper investigates the blast resistance capacity of a 6 storey building frame designed for extreme peak ground acceleration (PGA) levels of 0.5g, 0.4g, and 0.3g. The 3D model of the 6 storey building is designed according to Indian Standard (IS) codes for the above mentioned extreme level earthquake. Designed buildings are subjected to surface blast of 500 kg of TNT(trinitrotoluene) at different standoff distances ranging from 5m to 30m. The time histories of the blast loading due to air pressure and ground shock are modeled by those existing literature. A nonlinear time history of analysis (NTHA) of the frame is performed in SAP 2000 for surface blast and the simulated earthquakes from the specified response spectrum in IS code. NTHA results for both cases are compared to evaluate the relative performance of the three different seismically designed buildings to the surface blast loading. The response quantities of interest include maximum drift, maximum top displacement, and number of hinges formed. The results of the study indicate that for the near blast conditions the blast resistance capacity of the building increases with the increase in the PGA values for which the building is designed. By upgrading the seismic design by 0.1g, the blast resistance capacity increases manifold for near blast conditions. Thus, by updating the seismic design of a building, the risk of blast loading in the design may be considerably mitigated.

Experimental study of deep-burial underground structures subjected to multiple 45° side–top far-field explosions

A deeply buried straight-walled round-arch structure in a rock medium is taken as the research object in this study. Model tests of the underground structure subjected to multiple 45° side–top far-field explosions, with a scale of 1:20 and a proportional explosion distance of 1.68, are designed and carried out to study the dynamic responses, failure modes and damage mechanisms of the deep-burial underground structure after ground shocks induced by explosions. The macroscopic phenomena and measured data of the tests are reported and analyzed. The results show that after the first explosion and the second explosion, the surface of the surrounding rock model and the reserved charging port are seriously damaged. In contrast, the damage to the underground structure is relatively slight. The overall structure produces downward-bending deformation, and an axial crack occurs on the inner surface of the vault. The peak accelerations of the underground structure after the explosions are significant, with values reaching 2400 g, and the corresponding prototype value can exceed 120 g. After the first explosion, the damage to the upper part of the surrounding rock and the axial crack at the vault lead to a decrease in local stiffness. The crushed areas and cracks of the surrounding rock formed by the first explosion intensify the attenuation and leakage of shock wave energy during the second explosion, resulting in reductions in the ground shock pressure on the structure, the structural strain and the acceleration response. It is also found that on the floor of the prototype structure, the maximum spectral acceleration in the range of the natural vibration period of the human body exceeds 10 g, which poses a safety threat to the usage of underground structures. The research results in this study provide an experimental reference for the anti-explosion design of deeply buried underground structures and provide a basis for the establishment of performance and vulnerability indicators for straight wall round arch underground structures subjected to far-field explosions.