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Based on the comprehensive analyses of many risk factors leading to accidents in immersed tunnel engineering, it is concluded that the risk factors leading to accidents in immersed tunnel engineering are very large and must be paid attention to in all aspects at all stages of the project. This paper classifies and identifies the risk factors in immersed tunnel engineering by investigating and visiting the relevant investigation, design and construction units of immersed tunnel, and then puts forward prevention and control measures to provide theoretical basis for the prevention of risk factors in Immersed Tunnel Engineering in the future and the risk management of the whole project.

The use of superfine particles has been found to be a promising method for accelerating cement hydration. Amorphous aluminum hydroxide (AH3) is a key hydration product in sulfoaluminate cements and our preliminary research work indicated that the ultrafine amorphous AH3 accelerates the hydration rate of sulfoaluminate cement-based grouting materials (SAGMs). However, the ultrafine AH3 tends to agglomerate easily, which affects its effectiveness. In this study, aluminum hydroxide-polycarboxylic acid superplasticizer (AH3-PCE) ultrafine composites were prepared using the sol–gel method, and their effect on the hydration and hardening process of SAGMs was investigated. The results showed that the particle size of the AH3-PCE ultrafine composites decreased and then increased with increasing amount of PCE and there was a strong interaction of AH3 with PCE through the oxygen atoms of C–O–C. AH3-PCE ultrafine composites provided nucleation for the growth of bayerite and ettringite (AFt). Moreover, the AH3-PCE ultrafine composites released aluminum ions and PCE in an alkaline solution at pH 12.5. The AH3-PCE ultrafine composites promoted cement hydration, adjusted the pore structure of the hardened paste, and improved the compressive strength at all ages owing to the synergistic effect of nucleation, aluminum ions, and PCE released from the AH3-PCE ultrafine composite. [ABSTRACT FROM AUTHOR]

Featured Application: These research results can be applied in forest fire suppression. This paper focuses on improving fire suppression performance through the use of compressed-air launching technology. A launch dynamics calculation model of a compressed-air launcher is presented, developed using VC++ programming, to simulate the acceleration process of a fire-extinguishing bomb in a barrel. By analyzing the influences of various structural and initial parameters on interior ballistics variations, the effectiveness of the calculation model and program in accurately simulating the launching process is demonstrated. The calculation results indicate that the bore pressure follows a similar trend to that of traditional gunpowder launching. Additionally, it is found that specific structural parameters, such as nozzle diameter and gas cylinder volume, have a direct impact on interior ballistics variations. Notably, the nozzle diameter positively affects the peak pressure, muzzle velocity, gas transfer efficiency, and launch efficiency. To ensure an optimal launch effect and efficiency, the nozzle diameter should be selected to be more than half of the launcher caliber. Similarly, the gas cylinder volume positively influences the peak pressure and muzzle velocity while negatively affecting the gas transfer efficiency and launch efficiency. Furthermore, the initial pressure in the gas cylinder exhibits a positive linear relationship with both the peak pressure and muzzle velocity but a negative linear relationship with the gas transfer efficiency and launch efficiency. The loading position minimally impacts the peak pressure and muzzle velocity but slightly enhances the gas transfer efficiency and launch efficiency. Finally, it is observed that launch angles do not affect the interior ballistic process. The research findings provide valuable theoretical guidance for determining the working parameters of compressed-air accelerated fire-extinguishing bombs. [ABSTRACT FROM AUTHOR]

For high value-added utilization of carbide slag and sequestration of CO2, spherical vaterite was prepared at atmospheric pressure using carbide slag as raw material and various additives. The effects of additive types, reaction temperature, impurities in carbide slag and reaction system on vaterite in calcium carbonate synthesis were investigated by X-ray diffraction, scanning electron microscope and fourier transform infrared spectroscopy. The results show that glycine and serine have significant effect on the formation of vaterite. The increase of reaction temperature is not conducive to the formation of vaterite. The impurities Al2 O3 and SiO2 in carbide slag induce Ca(OH)2 mineralization CO2 system to form calcite. Different reaction systems affect the crystal size of prepared vaterite, and the crystal size prepared by carbide slag-CO2 system is the smallest. In the carbide slag-CO2 reaction system at 15 °C, monodisperse vaterite type CaCO3 with rough protrusions on the surface can be prepared by adding glycine. The above results provide a simple method for preparing high value-added vaterite from alkaline industrial wastes such as carbide slag, and safely and effectively storing a large amount of CO2 greenhouse gases. [ABSTRACT FROM AUTHOR]