1. Introduction
In recent years, the international environment and security situation have deteriorated. At the same time, wars, terrorist attacks, and unintentional explosions occur daily. A review of the world’s development pattern reveals that global wars are less likely to occur than local wars. With the advancement of international integration, any country is more likely to be assaulted by international terrorist organizations, posing a serious threat to people’s lives and property, as well as a significant menace to the world’s economic development and social stability. As a result, worldwide interest in research on anti-blast and detonation protection of engineering structures has grown.
Currently, research on anti-explosion performance, failure mechanism, and damage characteristics of structures subjected to blast load is primarily focused on civil building structures, ships, and military facilities [
1,
2]. Several studies on the impact of explosions on structures (dynamic damage constitutive model of concrete, efficient numerical simulation theory and method, anti-explosion safety, and performance evaluation method) were conducted by research teams and relevant research institutions, yielding some results that may be useful in analyzing anti-bang safety problems in dam engineering [
3,
4,
5,
6,
7]. The structural form, geographical location, protection standards, and requirements of high dam construction, on the other hand, differ from those of civil structures, ships, and military projects.
Arch dams are becoming increasingly popular around the world due to their economic, reasonable, safe, and dependable characteristics. Warfare, terrorist attacks, and unintentional explosions are happening all over the world right now. The study of anti-detonation safety of structures has received a lot of attention in the field of structural protection. The anti-blast fortification of strategic targets such as critical economic, military, and civil infrastructure has posed urgent requirements and challenges to engineering and research institutions. However, as dam engineering technology has advanced, a large number of 100 to 300 m high concrete arch dams have entered the stage of explosive growth. Because of their significant political and economic benefits, high concrete arch dams have undoubtedly become a top focus of local wars or terrorist attacks. If the dam fails, it will cause massive disasters and losses for the nation and its citizens, with inconceivable consequences. The anti-seismic and anti-explosion performance of the dam has become the center of attention during the dam construction and maintenance process. Anti-terrorism has become the top priority of dam safety protection, particularly since the 11 September 2001, terrorist attack. Therefore, taking the bang load as an extreme load and studying the dynamic response, failure mechanism, and anti-burst performance of the high concrete arch dam under the action of blast load can provide a theoretical basis and support for the dam’s anti-bang safety evaluation and anti-detonation fortification so that the dam can better play to its economic and military benefits in normal operation, wartime, or terrorist attacks, which have significant military implications.
The dam may be subjected to air explosions from rockets and missiles or underwater explosions from torpedoes, detonators, deep-water bombs, and missiles in terrorist attacks or accidental explosions. However, due to the different physical properties of water and air, as well as the different interface effects with explosion products, the propagation characteristics of an explosion shock wave in water and air differ significantly. As a result, the dam’s dynamic response and failure characteristics under underwater and air explosion shock wave loads fluctuate considerably. Therefore, the dynamic response and failure process of the structure under the impact load of underwater and air explosions should be concerned. A dam collapse may cause more damage than a nuclear bomb, and the loss cannot be recovered in a short period.
During World War II, the British Royal Air Force carried out large-scale bombing raids on three dams on the upper Ruhr River in Germany. The explosion blew a large hole in the dams. The induced dam failure caused nearly 400 million tons of floodwater to flow out instantly, resulting in 30,000 deaths or missing people and destroying nearly 200 factories. The entire Ruhr Industrial Zone was razed to the ground, and the nearby arsenal was completely paralyzed, greatly accelerating Germany’s defeat and reducing the allies’ losses [
8]. In 2014, Russian troops demolished a concrete dam in Ukraine’s Kherson region to cut off water to Crimea. Before Moscow annexed Crimea, the dam was linked to a canal that supplied 85% of the peninsula’s needs [
9]. According to Ukraine’s infrastructure ministry, on 26 February 2022, at 3:50 a.m., the Ukrainian air defense shot down a Russian missile aimed at the dam of the Kyiv Reservoir. If the dam had been destroyed, the floods could have caused catastrophic casualties and damage, including flooding of residential areas in Kyiv and the suburbs, according to Ukraine’s waterways state enterprise. The collapse of the Kyiv Dam could result in the collapse of the Kaniv, Kremenchuk, and other cascade dams, as well as an accident at the Zaporizhzhya Nuclear Power Plant [
10].A dam strike has incalculable strategic significance in war.
The arch dam’s stress characteristic is that the load is transmitted to the rock mass and foundation on both banks through the arch [
11,
12]. The arch structure’s characteristics can save a lot of building materials. Its integrity has also improved. The thickness ratio from the dam bottom to the dam crest is much smaller than that of gravity dams, as is the thickness height ratio. Because of these characteristics, the thickness of the dam body corresponding to the detonation point is not large when the arch dam is subjected to an explosion impact at any point. When compared to the gravity dam, its anti-detonation safety performance will be significantly reduced [
13,
14]. To summarize, the impact of the burst load on the arch dam’s overall shell structure may cause it to collapse in a large area. A high-arch dam has a total storage capacity of nearly 20 billion cubic meters. When the overall regulation fails, a large amount of reservoir water is released instantly, causing unimaginable consequences [
11,
12] As a result, research on the safety performance of arch dams under extreme detonation impact loads is an important topic. The structure’s response to an explosion load is a complex physical process that includes the explosion of explosive materials, the propagation of a blast shock wave, the dynamic interaction of the shock wave and the structure, and the resulting structural response. The key to determining the mode and magnitude of the bang load in the damage analysis of the dam subjected to the blast impact load is how to determine the mode and magnitude of the detonation load. As a result, a coupling model that fully considers each physical process of an explosion and proposes a calculation method suitable for large scale and high non-linearity is required. At the moment, experimental research and numerical simulation are the major approaches for studying the dynamic response and failure mechanisms of structures subjected to blast impact loads. However, when the test method is used to study the dynamic response and failure mechanism of the dam under an explosion impact load, there are still few test research data and limited test data on the response and failure mechanism of the dam under an explosion load due to limitations in test conditions and test funds, as well as insurmountable disadvantages such as difficult data acquisition, data error, and environmental impact. With the gradual improvement of computer hardware and calculation methods, it is now possible to use a numerical simulation method to simulate the response of an explosion load to a structure.
When using a numerical method to simulate the energy propagation of a blast shock wave, the calculation results are greatly affected by the finite element mesh size. This is because if the mesh is too large, it will have a filtering effect on the shock wave generated by the explosion, resulting in a significant loss of shock energy. Therefore, a smaller mesh size is typically used in the research process. Some researchers believe that, while a mesh size of 500 mm cannot accurately capture the peak pressure generated by the detonation shock wave, the impulse value can [
15]. According to research, a mesh size of 200 m can effectively simulate the impact energy of explosion shock waves. When the detonation distance is long, the mesh size can be increased to meet the requirements of maintaining calculation accuracy while also improving calculation efficiency.
An arch dam is a massive water-retaining structure. The world’s highest arch dam currently stands at ≤300 m. The dynamic interaction process of the entire arch dam body, reservoir water, air, and foundation system under a bang load is relatively complex and difficult to realize. If a fine mesh size of 200 mm is used for division, the final mesh number will be enormous, and the calculation model will take up a large amount of computer memory. The calculation time will be extremely long, and the calculation result will be enormous, both of which are difficult for ordinary computers to achieve. The dam model is scaled by dimensional analysis. That is, the explosion similarity law is used to simulate the dynamic response and failure characteristics of the arch dam after detonation. It is a feasible scheme to apply the scaling model results to the actual arch dam structure. Experimenting under the influence of a blast is costly, dangerous, and difficult to collect data from. As a result, numerical methods are used to simulate structural damage and failure caused by an explosion. If a simulation of equal size is used for research on the dynamic response and failure mode of tall buildings under discharge load, the number of meshes will be enormous and the calculation will be impossible to perform. Therefore, the detonation similarity law is required, the dimensional analysis method is used to establish the proportional relationship between various parameters in the blast process, and the numerical simulation analysis of buildings is carried out using the scale model. The law of explosion similarity clearly describes the regular relationship between bang energy and structure damage results, and large structural damage results can be obtained from failure parameters of small structures, and large structure explosion parameters can be converted from the blast phenomenon of small charges.
Because of the serious consequences, the dam’s safety and protection from strong explosion impacts are important considerations. Consequently, a fully coupled model of a concrete arch dam under an explosion impact is established in this research paper using Lagrangian and Eulerian coupling methods. Taking into account complex issues such as the high strain rate effect of concrete under the action of an explosion, the dynamic interaction between shock wave and structure, and the dynamic response of the structure, the reliability of the coupling model is validated by comparing it to previous research results. The effects of underwater and air blast shock waves on dam dynamic response, damage degree, damage mechanism, and anti-explosion performance are investigated. The effect of explosive initiation distance, explosive amount, initiation depth, and reservoir water level on the dam’s anti-explosion performance is discussed. Simultaneously, based on the damage and failure level proposed in this paper, the most influential factors on the dam’s failure state are identified; the typical damage and failure modes and characteristics are obtained for various failure states; the dam damage prediction model under an underwater explosion impact is established, and the dam damage prediction key curve is divided into different failure levels; the dam’s safe initiation distance under the impact load of an underwater explosion is determined, and a damage prediction flow chart is provided, which can serve as a foundation and reference for damage prediction of other dam types. Furthermore, the protective effect of foamed aluminum material on the dam body’s anti-explosion performance is being studied, which has the potential to significantly reduce the dynamic response and damage of concrete arch dams while also improving their anti-explosion capability. Overall, the results of this study have important theoretical and engineering implications for improving the anti-explosion safety of concrete arch dam structures.