Protection Of Underground Structures Research Articles

Study on the Protective Effect of Viscous Buffering Device under Explosive Load

In recent years, with the complex and changeable international situation, local wars and conflicts abroad have occurred frequently, which seriously threaten the safety of human life and property. Against this background, high-precision and high-intensity strikes against key targets such as enemy command posts and ordnance reserves have become the norm in modern warfare. As the undercard of national security, the security and protection capabilities of underground military facilities are of great importance. Underground structures not only play the role of emergency evacuation of personnel to avoid air and missile attacks, but also the core of the combat command system, where key facilities such as military underground factories and warehouses are located. The security of these facilities has a direct bearing on the outcome of a war and even the fate of a country. In view of this, taking effective measures to improve the explosion resistance, durability and survivability of underground protective structures has become an important research topic in the field of military engineering in various countries. Under the action of the explosion of conventional weapons at a certain distance, the underground protective structures can be damaged due to insufficient resistance. The powerful shock wave generated by the explosion, with its huge kinetic energy and impact force, will cause a large vibration acceleration ring inside the structure, which is very easy to cause casualties and equipment damage within the structure, thus posing a serious threat to the safety of underground engineering. In order to improve the anti-explosion performance of the protective structure under the action of blast impact load, the underground protection engineering structure has been continuously upgraded and optimized, among which the layered protective structure has been widely used because of its relatively excellent protection effect. The layered protective structure realizes a relatively effective protection system through a well-designed camouflage layer, a bullet shielding layer, a dispersed layer and a main structure. However, although significant progress has been made in the optimization of three-layer materials, the defects such as the unstable state of the dispersed layer and the possibility of reducing the overall protection performance with time or external conditions are still an urgent problem to be solved. This system is designed to replace or partially replace the traditional dispersed layer, which is not only designed to effectively absorb and dissipate the blast wave energy transmitted by the bomb shielding layer, but also fundamentally solve the problem of the reduction of protection effect caused by the change of the state of the dispersed layer. In this study, the simulation technology will be used to deeply explore the structural dynamic response of the protective structure after the addition of buffer energy dissipation device under the blast impact load, and the key factors affecting the protection effect will be systematically analyzed, the simulation parameters will be accurately set, and the protection effect under different parameter combinations will be simulated, so as to find an optimal parameter configuration scheme. This study not only helps to deepen the understanding of the anti-explosion performance of underground protection structures, but also provides valuable theoretical basis and practical guidance for the design and construction of underground protection projects in the future.

Numerical Integration Study of Penetration and Blasting Damage for Composite Underground Protective Structure with Reinforcement Layers

In response to the increasing threat of powerful earth-penetrating weapons, underground protective structures typically employ composite structural systems with reinforced steel layers. However, current numerical studies often simplify the entire structural system to plain concrete when assessing damage effects, and penetration and blasting processes are treated separately using a restart method. In this paper, we adopt an integrated simulation approach to analyze the resistance performance of composite protective structures with reinforcement layers. The results reveal significant differences in failure modes between plain concrete and reinforced concrete protective structures. The diameter of the steel bars and the spacing between mesh layers notably impact the penetration and blasting damage. Based on the results of a parameter analysis, we propose a method for optimizing the design of reinforcements in composite underground protective structures. The results of the study show the following: (1) The penetration and blast damage patterns of EPWs on plain concrete and composite protective structures with reinforcing mesh are significantly different. Compared to the plain concrete layer, the composite protection structure can effectively resist the damage of EPWs. (2) With the increase in reinforcement diameter, the decrease in reinforcement mesh spacing, and the increase in reinforcement dosage, the penetration depth gradually decreases; the amount and range of the blast damage also decrease accordingly. (3) Under the condition of the same reinforcement ratio, reducing the number of layers of reinforcement mesh, increasing the diameter of reinforcement, and configuring the reinforcement on the top of the protective structure as much as possible can improve the performance of the protective layer against penetration. At the same time, the reasonable arrangement of the reinforcement mesh can also enhance the ability of the protective structure to resist blasting damage.

Symmetric elastic wave cloak design for underground protective structures based on multi-center coordinate transformation

Symmetric elastic wave cloak design for underground protective structures based on multi-center coordinate transformation

Explosion Behaviors of Scaled Shallow-Buried Concrete–Rubber-Laminated Annular Metastructures: Evaluation of Shock Wave Attenuation

The attenuation of impact inducer vibration is critical to the safety of underground protection structure, equipment and personnel. Metamaterials and metastructures show great potential in terms of sound and impact attenuation. To effectively attenuate ground shock-induced vibration of underground protective structures, scaled shallow-buried annular metastructures with concrete–rubber layered structures were proposed and constructed. Underground explosion experiments were performed to investigate the vibration attenuation effect of annular metastructures with different layered structures. It is clear in this research only annular metastructures with concrete–rubber–concrete structures like annular metastructure model B6 have the most excellent wave attenuation performances, whose rubber layer thickness must be over 6[Formula: see text]mm and hardness is 20[Formula: see text]HA. Other layered structures with rubber layer thickness of 0.3[Formula: see text]cm or with more layers cannot effectively attenuate the shock wave in this research.

Field test and theoretical analysis of a large underground arch structure subjected to buried explosion

Underground arch structures play a crucial role in protective engineering. However, with the advancement of military technology, buried explosions caused by earth penetrators have emerged as a significant threat to these structures. To investigate the dynamic response of underground arch structures subjected to buried explosions, a large arch structure was designed and constructed in a weathered basalt mountain, followed by field explosion tests. During these tests, various parameters such as pressure, velocity, acceleration, and displacement of the structure were recorded and analyzed. The test results demonstrate that conducting field explosion tests on a large arch structure facilitates the acquisition of detailed and comprehensive insights into the dynamic response of underground arch structures. When subjected to overhead explosions, the structure exhibited an overall response, with a noticeable local effect. The dynamic response of the arch was found to be significantly larger than that of the floor slab. Additionally, as TNT mass increased, the response of the structure became more intense, while its rebound ability weakened. The acceleration frequencies of the structure were primarily concentrated in the low-frequency ranges. Furthermore, the dynamic response of the structure was analyzed using a simplified load model and modified governing equations. The proposed theoretical analysis model effectively predicted the peak displacement of the arch. These research findings can serve as a valuable reference for the design of anti-explosion in large underground protective structures.

Close-in explosion behaviors of scaled concrete–rubber layered circular meta-tunnels

Attenuating shock-induced vibration is crucial for the safety of underground protective structures, equipment, and personnel. Metamaterials and metastructures demonstrate great potential for sound and shock attenuation. However, to further enhance protection against blast shock waves, more rational metamaterials and metastructures need to be proposed and designed. Additionally, more experimental and theoretical studies are required to explore the vibration attenuation mechanisms and effects of these metastructures. To this end, this study proposes layered meta-structures consisting of stiff concrete layers and thin, soft rubber layers. Scaled meta-tunnel models were constructed, and close-in explosion experiments were carried out to investigate their vibration mitigation performance. The impacts of critical parameters, including layer materials, layer thickness, and scaled distance, on the vibration attenuation effects were investigated through comparing displacements, strains, acceleration data, and failure characteristics. The results reveal that under close-in field explosions with small TNT mass all these scaled models have greater displacement and more cracks, for laminated structure weakens the integral rigidity of the metastructure. Under great TNT mass, the difference gets much smaller. But all these structures have excellent vibration attenuation. The acceleration attenuation rate exceeds 98% for two-concrete-layered models with rubber layer thickness of 0.6 cm under explosion with TNT mass of 0.1 kg and stand-off distance of 1.0 m. When the TNT mass increases, the acceleration attenuation ability will be weakened. In this research, more layers will improve vibration attenuation only under high equivalent explosions as fracture of each layer will dissipate more energy. Overall, this study sheds light on the efficacy of meta-structures in attenuating vibration induced by explosive blasts and lays the groundwork for more sophisticated and advanced protective engineering designs.

The Attenuation Ability of Saturated Joints Filled with Granular Materials under High-Amplitude Stress Wave Loading

Existing experimental evidence shows that the propagation of explosive waves in the free fields of soils is remarkably affected by the degree of saturation. In the surrounding rocks of underground protective structures, the underground water is normally unavoidable, which is supposed to reduce the isolation efficiency of a passive antiblast barrier. To investigate the effect of water saturation on the stress wave attenuation ability of infilled joints, impact tests were carried out on artificial joints filled with dry and saturated granular materials using a split Hopkinson pressure bar (SHPB). The test results revealed that under the same conditions, the stress and energy transmission coefficients of the waves crossing saturated sand-filled joints were about 3.16–4.13 times and 9.75–11.4 times those of joints filled with dry sand, respectively. The dynamic stress-strain relationship of the filling layer during the impact process and the crushing index of the infill were analyzed. The results showed that the compressibility and the granular crushing index of the dry sand were much greater than that of the saturated sand, and the dynamic stress-strain relationship of the dry sand exhibited three-stage nonlinear characteristics. The experimental results quantitatively uncovered the serious adverse effect of water on the wave absorption properties and markedly diminished the potential of the filled joints as a wave elimination barrier, which should be a matter of great concern in the design of underground protective structures.

Effects of EPS density on blast mitigation performance in underground protective structures

Explosions due to terrorist attacks or accidents can cause severe damage to critical infrastructure. To protect important facilities from blast damage, they can be constructed belowground. Further, an explosion mitigation layer consisting of soil and foam material can be used to provide additional protection. In this study, the effects of expanded polystyrene foam (EPS) density on blast mitigation system effectiveness were investigated experimentally. From the test results, an equation that estimates the optimum EPS density to most effectively reduce peak blast pressure is proposed. Moreover, equations for estimating the peak pressure and scaled impulse at the bottom of a mitigation system, which account for the effects of EPS density, have also been proposed.

Effects of a protective metal sheet of an EPS plate on blast mitigation performance in underground protective structures with blast mitigation layer

Effects of a protective metal sheet of an EPS plate on blast mitigation performance in underground protective structures with blast mitigation layer

Methodological and scientific approach into the process of calculation a multilayer underground protective structure

During the Joint Forces (anti-terrorist operation) operation in Donetsk and Luhansk oblasts, civilians and the Armed Forces suffered significanted losses.
 As a result, we have needed to study impact various weapons on structure roof of buildings which built of different materials to improve protective properties is becoming relevant.
 Therefore, in modern conditions, design of structures and their elements is not possible without taking into account impact of shells. When designing and constructing structures, it is always necessary to take into account resistance of structural elements to impact of damaging factors, both explosion in general and destructive explosion in particular, which will help avoid future possible human losses.
 The article presents model of calculation shell penetration into soil thickness covered shelter, consisting of scattering, mattress, distribution layer, load-bearing structure and impact of shells, mines and air bombs to penetrate the thickness of closed structures.
 The purpose article is to highlight main provisions scientific and methodological approach to calculation multilayer underground protective structures and studies impact of projectiles on multilayer underground protective structure.
 Our research shows that to determine protective thickness mattress of structure, during penetration of ammunition, first of all, should take into account resistance to scattering, and to determine thickness distribution layer resistance of mattress.
 Depth of penetration projectile into thickness floor structure will depend on: mass, diameter, shape of main part projectile, as well speed and angle at meeting of projectile with the floor structure.

Numerical simulation of surface blast reduction using composite backfill

Underground protective structures are usually made of reinforced concrete at a certain depth below the surface that is covered with soil. Materials, layering and geometry of the composite backfill play important roles in damping the stresses caused by surface blasts. The current study used 3D modelling to investigate the characteristics of the composite backfill subjected to surface blast load. The results indicated that the application of geofoam as a geosynthetic isolator layer increased the percentage of pressure decay (PD) up to 61%. Comparison of the different materials used for pressure mitigation revealed that a 0.75 m thick layer of geofoam performed similarly to a 1.1 m thick layer of unreinforced concrete, a 0.75 m thick layer of reinforced concrete with a steel equivalent height of 0.06 m and a 0.37 m thick steel layer. The combined use of reinforced concrete and geofoam considerably increased the PD.

On Stress–Strain Function of Geomaterials Subjected to Blast-Loads

An appropriate stress–strain relationship of geomaterials subjected to blast loading is essential for the design of underground protective structures. Previous experimental and theoretical research efforts indicate that the constitutive behavior of geomaterials under blast loading depends upon strain rate, stress level, and interaction among the three phases (solid, liquid, and gases). In current state-of-the-art, various advanced constitutive models are available to model the stress–strain behavior of geomaterials under blast-loads. However, considering the cost of computation associated with such models, a functional form is discussed to model the loading and unloading branches of stress–strain curve of geomaterials subjected to blast load based on the three parameters: weight factor, initial modulus ratio, and strain recovery ratio. It is observed that the new functional form reasonably captures the mean trend of the experimentally obtained or simulated stress–strain data. This paper further investigates the applicability of this functional form and provides a catalog of the model parameters for direct use by practicing engineers. The dependence of function parameters on strain rate, lateral confinement, degree of saturation, initial compaction, and locking initiation stress is investigated, and some simple rules are proposed for reasonable estimation of the three parameters. The proposed functional form would be quite useful in practical design problems specially where cost of computation associated with advanced constitutive models is too high. In addition to this, the proposed simple parametrization of complex nonlinear stress–strain behavior also provides an opportunity to investigate the effect of uncertainties in soil parameters in a computationally efficient manner.

Development prospects of creating armo-bearing shells theory

Abstract. In the article, the prospects for the use of load-bearing armored shells are discussed, which create the possibility of their application in the arising zones of stress concentrators, increased fracturing or zonal disintegration (ZDI) for the formation of objects of special-purpose or with special characteristics. This increases the resistance of the rock mass due to the use of special materials with certain properties (hydrophobic additives, etc.), which in total makes it possible to create formations for various purposes and with specified parameters. Technical problems in the construction of underground structures are mainly caused by the need for the creation and subsequent operation of the internal space. For example, in relation to solving the problems of underground construction of special structures, construction of underground gas storage facilities (UGS), underground construction of protective structures (bomb shelters), construction of earthquake-resisting structures and buildings. The main problems of underground construction, its technical capabilities and solutions are considered. The possibility of using the worked-out underground space of mines is shown in connection with the problems of construction of underground protective structures (bomb shelters), underground gas storages. The possibility of using the phenomenon of zonal disintegration (ZDI) as the main economic prerequisite for the construction of earthquake-resisting buildings and structures in regions with earthquake-resisting mining and geological conditions is proposed, and schematic diagrams of technological solutions are given. The tasks are considered, the solution of which is of paramount importance for the problems listed above. The prospects for the application of technologies for the formation of load-bearing armored shells (LBAS) in conditions of zonal disintegration (ZDI) are shown, namely: control and forecasting of the occurrence of the phenomenon of the rocks ZDI in the course of various underground construction works; control of the state of the massif in which the LBAS are constructed to ensure the specified operating parameters; the use of the fracture zone between the rings of disintegration for filling with materials with certain properties (hydrophobic impurities, etc.), which ultimately makes it possible to create formations for various purposes and with specified parameters.

Concrete protective arches reinforced with BFRP bars: Construction and quasi-static structural performances

To construct corrosion resistant protective underground arches in waterfront structural engineering, steel bars are replaced by basalt fiber reinforced polymer (BFRP) bars and hybrid BFRP-steel bars. Eight semi-circular arches reinforced with steel bars, BFRP bars and BFRP-steel bars were casted. Quasi-static compression experiments were performed to evaluate the structural performances of the arches, including the deformation types, the failure modes and the ultimate loading capacities. Although the composite bars are linear elasticity, the concrete arches reinforced with composite bars behave as elastic-plastic deformation. The arches have typical flexural failure mode when the failure is determined by the crushing of the compressed concrete. Meanwhile, some of them exhibit brittle failure when the vault of the arch is sheared to fracture. Compared with the steel bars reinforced arches (SBRAs), the BFRP bars reinforced arches (BBRAs) have comparable ductility and ultimate loading capacity. An analytical method of the structure, including the coupling effects of bending moment, axial force, and shear force, was proposed to predict the load capacity of the SBRAs and BBRAs. The results show that the new proposed analytical method can capture the experimental results with acceptable errors. According to the experiments and analytical results, the BBRAs with excellent corrosion resistance can be treated as a replacement of SBRAs in waterfront underground protective structures.

Performance and evaluation of an EPS plate to mitigate blast on underground protective structures

Explosions due to terrorist attacks or accidents can cause severe damage to critical infrastructure. To protect important facilities from explosion damage, they can be constructed belowground. Further, an explosion mitigation layer can be used to provide additional protection. In this study, an expanded polystyrene (EPS) plate has been incorporated into the soil layer for blast mitigation, and the performance of the system has been investigated experimentally. The results indicate that there is an optimum ratio of sand layer thickness and EPS plate thickness for decreasing and dispersing blast pressures. Formulas describing the peak pressure and scaled impulse on the bottom of the mitigation system as functions of a scaled distance from directly under the explosion source and scaled layer thickness have been derived.

Waterproofing material for protection of underground structures

The article deals with the problem of increasing the durability of underground and buried buildings. One of the methods of solving this problem is ensuring the reliable protection of underground structures from the effects of water of different origin. Among the existing waterproofing coatings, mineral-based compositions are the most effective. However, the main disadvantage of such systems is the low crack resistance of hard coatings, which limits their applicability. We have made an attempt to develop a cement-based waterproofing material that would have high elasticity, strength, crack resistance and adhesion to a concrete base. We have conducted studies to justify the possibility of obtaining an effective waterproofing material by including microsilica and ethylene vinyl acetate in the mix. The optimal composition of the material was worked out. On the basis of the experimental data, the main physical and mechanical properties of the material were established. Based on the obtained results, it was found that the resulting material had high physical and mechanical characteristics and could be recommended for the protection of concrete structures used in underground construction.

Blast responses and damage evaluation of CFRP tubular arches

Concrete-filled carbon fiber reinforced polymer (CFRP) tubular arches have been constructed as the load-carrying structure for bridge engineering over the last decade in the US. To investigate the dynamic responses under blast loading, four scaled tubular arches with different CFRP strengthening ratios and concrete strength were researched. The TNT explosive remained 2.0 kg while the standoff distance was set as 0.76 m and 0.4 m, respectively. The damage modes of the tested arches were observed. The dynamic responses including displacement histories and reflected pressures were recorded. According to experimental results, blast-resistance of tubular arches could be enhanced by improving the CFRP strengthening ratios and concrete strength. In addition, residual load capacities of these arches were tested. A factor to evaluate the damage of the arches under explosion is defined. Simplified theoretical models were suggested and discussed, which can be used to predict the ultimate load of the arches. Both the blast test and the subsequent residual load capacity test reveal that this composite tubular arch has the potential to be constructed as underground protective structures.

The influence of the internal microbiome on the materials used for construction of the transmission natural gas pipelines in the Lodz Province

This paper presents investigation results of the influence of gas microbes on the biocorrosion rate of the materials used for gas pipelines construction in the Lodz Province. Samples of two types of carbon steel and cast iron were stored in the laboratory pipeline model reflecting the real conditions of working natural gas pipelines were. In the next step the influence of cathodic protection with parameters recommended for protection of underground structures was tested. Analyses of biological corrosion products generated on the test surface were carried out using a scanning electron microscope with an X-ray analyzer. The level of ATP was measured to confirm presence of the adsorbed microorganisms on the observed structures. Corrosion rates were determined by gravimetric methods. In the course of the study it was revealed that the rate of biocorrosion of steel is lower than that for cast iron. Our results also proved that the weight corrosion rate depends on the number of adhered microorganisms. In addition, it has been found that application of the carbon steel cathodic protection decreases its weight corrosion rate. The information obtained will help to increase the knowledge on the rate of biological corrosion causing losses/pits inside gas pipline.

Air-blast Induced Ground Displacement

Outburst of nuclear explosion produces moving air-overpressure above ground surface. These overpressure fronts move at super-seismic speeds near ground zero and cause ground motion. Hence, determination of air-blast induced ground displacement is the first essential step in design of underground protective structures in super-seismic zone. For simplified analysis, air-blast load is modelled as linearly decaying pressure with time and using one-dimensional elastic wave propagation model, free-field vertical displacement response of elastic half-space can be expressed as a closed-form solution. However, such a simplified solution seems to be of very little practical utility in addressing problems in geotechnical environment. Hence, a new closed-form solution is proposed for displacement time-history which accounts for linear-inelasticity, plastic wave propagation velocity, and geometric stress attenuation. A conceptual pseudo-static procedure which computes vertical displacement as a static problem at each time instant based on dynamic properties of geomaterials is utilized to achieve the proposed solution. Predictions of the proposed model are compared with results of one of the atmospheric nuclear tests conducted at Nevada Proving Grounds and a reasonable agreement is obtained.

Pre-grouting for Leakage Control and Rock Improvement

In underground construction, ground water inflow and rock mass stability has been a challenging problem. Especially the tunnels constructed below ground water table are often exposed to risk of ground water inflow. Protection of underground structures against water ingress and rock mass failure is of paramount importance during construction as well as operation of the tunnel. Risks associated with these hydrogeological issues often pose challenge to tunneling engineers. Mitigation of these risks by means of pragmatic measures such as pre-grouting can improve the rock mass strength and restrict the water ingress to acceptable levels. The primary purpose of pre-grouting is to improve the rock mass strength and establish an impervious zone around the tunnel periphery, thus leading to reduced support system and permeability of rock mass. The aim of this article is to discuss the concept of pre-grouting as an effective mitigation measure for leakage control and rock mass improvement which is being successfully implemented in many countries.