A lightweight and efficient two-stage video flame detection algorithm was designed to address issues of high false positive rates, poor adaptability, and low efficiency in complex scenes. In the first stage, an improved adaptive Gaussian mixture model (AGMM) was employed for rapid background modeling of video image sequences. Suspicious candidate regions were extracted from the sequences by leveraging the flickering and surging characteristics of flames. In the second stage, a residual deep normalization and convolutional neural network (ResDN) was used to discriminate these suspicious candidate regions. A simplified residual block was introduced to replace the original convolutional layers for a lightweight design, enabling accurate flame detection and localization. Compared with traditional classification algorithms, the proposed two-stage video flame detection algorithm effectively overcomes environmental interference in complex scenes, rapidly and accurately identifies flames, and demonstrates higher detection rates and adaptability.

Understanding the failure mechanism of cracked rock mass under the general stress state is essential for underground engineering construction safety. A series of true triaxial fracture tests on the sandstone with single pre-existing flaw were conducted. The failure modes of the cracked sandstone were analysed, and the multi-scale fracture characteristics and mechanisms of the basic types of crack were identified. Moreover, the influences of the stress state and the pre-existing flaw on the rock failure mechanism were summarized. The results indicate that the rock failure mode is controlled by the true triaxial stress and the pre-existing crack. Based on the multi-scale fracture characteristics, the fracture mechanism of the crack. The rise of minimum principal stress σ₃ can significantly reduce the percentage of the shear crack, while the rise of intermediate principal stress σ₂ conduces to the increase of the percentage of the tensile crack. The pre-existing flaw has a certain promoting effect on the initiation of the tensile crack, however, the true triaxial stress is the decisive factor controlling the rock failure mechanism.

In order to analyze the influence of evolution of the dominant order of wheel polygonal wear on the vibration response of the train-bridge coupling system, the key influencing factors and evolution patterns of the dominant order of polygon wear were summarized first. Meanwhile, the coupled dynamic model of the train-bridge system was established by utilizing a combined simulation approach with ANSYS and SIMPACK. Subsequently, the impact of evolution of the dominant order of wheel polygonal wear on the vibration response of the train-bridge coupled system under different operational mileages, train operating speeds, vertical stiffness of fasteners, and variations in wheel diameter, was explored. The research results indicate that the evolution of the dominant order of wheel polygonal wear significantly affects the dynamic response of the train-bridge coupled system. In general, when the wheels experience high-order polygonal wear, the lateral and vertical accelerations at the mid-span of the bridge increase significantly. Moreover, the wheel-rail force and derailment coefficient also increase significantly, with the train wheels experiencing momentary bouncing. This has an impact on both the quality of high-speed train operation on the bridge and the safe operation of the bridge structure, necessitating timely wheel re-profiling.

In order to speed up the engineering progress, early strength additives are usually added to improve the early strength of cement grout. Calcium chloride, sodium sulfate, triethanolamine, synthetic calcium formate, HR-SA1 and other early strength additives were selected, the flowability, shrinkage rate, and compressive strength of cement slurry under the action of different early strength agents were explored through indoor experiments. In this way, the influence of different types of early strength agents on the early physical and mechanical properties of cement slurry were revealed. The results show that all early strength agents can meet the needs of on-site grouting requirements, ensuring that the fluidity of the cement slurry can be stable for a long time. The flowability of the synthesized calcium formate-based cement slurry significantly increases within 60 minutes, indicating a notable retarding effect. The fluidity of the other early strength agents cement slurry slightly increases within 60 minutes, but the amplitude is not significant. The compressive strength of (HR-SA1)-cement slurry specimens at all ages is significantly higher than that of ordinary cement slurry specimens, while the other four early strength agents have no significant effect on improving the compressive strength of cement slurry. The average shrinkage and shrinkage rate of (HR-SA1)-cement slurry specimens after final setting are very low, far lower than the average shrinkage and shrinkage rate of other early strength agent cement slurry specimens. It is verified by the construction site of prestressed anchor cable of a subway station in Qingdao City. The test values of the physical and mechanical properties of cement slurry are basically consistent with the results of laboratory test, which lays a foundation for the popularization and application of HR-SA1 early strength agent in practical engineering.

In response to the shortcomings in the construction of temporary support for tunnels, a assembly of temporary support was proposed, and the new structure was studied from the aspects of temporary support shape, assembly structure, and stress deformation. Taking the Shaojiatang Tunnel as the background, on-site monitoring data was collected and compared with traditional temporary support structures using finite element software. It can be concluded that excavation of the tunnel’s rear tunnel will have adverse effects on the deformation of the previous tunnel. Vertical temporary support has better control over the left and right arch waists, surface settlement, and total convergence deformation of the tunnel. Compared with traditional curved structures, it decreases by 16%, 20%, 55%, and 14%, respectively. Moreover, vertical temporary support can restore stability faster and shorten the dismantling distance. By using vertical temporary support, the initial support force of the tunnel is smaller and safer compared to the curved support, and the maximum vertical and lateral stresses are reduced by 58% and 73%, respectively. The mechanical characteristics of temporary support local structures were simulated using ABAQUS software. The results show that the forces and deformations of both prefabricated vertical and traditional temporary support structures can meet the requirements of the specifications. However, prefabricated temporary support structures have more advantages in construction efficiency and economic benefits, and choosing prefabricated temporary support is more suitable.

In order to improve the traffic efficiency of aircraft routes in areas affected by strong convective weather and optimize the diversion path of aircraft under the influence of strong convective weather, a multi-objective diversion path planning method based on the non-dominated sorting genetic algorithm III(NSGA-III) was proposed. By constructing a flight environment model and delineating flight restricted areas according to airspace conditions, and on this basis, focusing on the impact of strong convective weather in the area where the aircraft was diverted, the aircraft operation cost was the lowest, the diversion angle was the smallest, and the non-linear coefficient was the smallest, with the goal of minimizing the impact of weather, using NSGA-III to comprehensively considered factors such as safety and economy and other factors, a multi-target diversion plan for a certain airspace route under severe convective weather was carried out, and simulation analysis was conducted. The research results show that NSGA-III can comprehensively consider the four proposed goals and calculate multiple effective alternative diversion paths. Under the conditions of selecting two diversion points and taking into account the economy and rationality of the operation while ensuring the safe operation of the aircraft, a total of 91 alternative routes are available.

In order to cope with the rapid recovery and growth of air passenger flow and the uncertainty of passenger group structure and consumption behavior, and to give full play to the role of aircraft parking stands resources in improving non-aeronautical revenue, an optimal allocation model for aircraft parking stands based on the maximization of flight route commercial value was established. Firstly, the game theory combinatorial weighting method was used to correct the influence of subjective factors on the evaluation results. Then, the commercial value of aircraft parking stands and flight routes was quantitatively ranked by the VlseKriterijumska optimizacija I kompromisno resenje(VIKOR) algorithm, which could eliminate the mutual influence of multiple indicators. Finally, a trunk airport in northern China was used as an example to verify the feasibility of the method. The results show that three evaluation indicators of commercial value of flight routes are significantly correlated with the per customer transaction at boarding gate and commercial concentration zone, including departure time, dwell time and daily average passenger volume. By reasonably matching flight routes and parking stands based on commercial value, the commercial value of boarding gate and commercial concentration zone can be increased by 9.4% and 6.2% respectively. Therefore, introducing the commercial value of flight routes into the traditional aircraft parking stands allocation model has important practical application value for increasing airports non-aeronautical revenue.

In order to investigate the durability of fibergypsum-based cementation material, a composite material was prepared byincorporating polypropylene and ramie fibers into high-strength gypsum,fly ash, and slag in a ratio of 44:34:22. Sodium methylsilicate wasutilized for waterproofing the fiber gypsum-based cementitious material,and the effects of freeze-thaw cycles on its softening property, waterabsorption, and mass loss were studied after 5,15,25,45, and 90 daysunder the combined action of ${\mathrm{H}}_{2}{\mathrm{{SO}}}_{4}$ or $\mathrm{{NaOH}}$ corrosion andfreeze-thaw. Freeze-thaw strain testing, flexural and compressivestrength testing, as well as industrial computed tomography(CT) scanningwere conducted. The results indicate that fibers can mitigate bothelastic and plastic deformation of the gypsum-based cementitiousmaterial during freeze-thaw cycles. Furthermore, under the combinedeffect of acid-base corrosion and freeze-thaw cycles, NaOH causesgreater damage than ${\mathrm{H}}_{2}{\mathrm{{SO}}}_{4}$ does.After undergoing 90 days of freeze-thaw cycling with sodiummethylsilicate treatment applied to it, the flexural and compressivesoftening coefficients increase by 0.28 and 0.13 respectively comparedto specimens without waterproofing; meanwhile water absorption ratesdecrease by 1.56% while mass loss rates decreased by 9.52%. Asfreezing-and thawing times increase, pore development in specimens isstill dominated by small holes, and crack diameters are mainly between ${0.1}\sim 2\mathrm{\;{mm}}$ .

In order to investigate the feasibility of applying solidified shield muck in road construction, the shield muck from Nanjing Metro was taken as the research object, and the green polymer composite curing agent developed independently was used to solidify the shield muck. The impact of the curing agent dosage and maintenance age on the road performance indicators of the shield muck was analysed using various tests-unconfined compressive strength, direct shear test, California bearing ratio (CBR), resilient modules, and freeze-thaw cycle test. In addition, the micro-characteristics and solidification mechanism of the solidified soil were investigated by scanning electron microscope and X-ray diffraction. The results indicate that the composite curing agent can effectively improve the strength of solidified muck, and with the increase of curing agent dosage and maintenance age, the strength of solidified muck also increases. The CBR and resilient modulus of solidified shield muck substantially improve as the dosage of the curing agent elevates, and the solidified soil can well meet the requirements of the Specifications for Design of Highway Subgrades (JTG D30—2015) and Specifications for Design of Highway Asphalt Pavement (JTG D50—2017). The freeze-thaw resistance of shield muck is poor, while it can be effectively improved after curing treatment. The strength loss and mass loss of solidified soil are less than 20% and 1% respectively. The anti-freezing performance indicators meet the requirements of the specification. After the curing agent has been added to the soil body, the polymer components will absorb water and dissolve, creating a static chelating effect with the mineral ions in the soil, initially reducing the water content of soil and promoting the agglomeration between the soil particles. Meanwhile, the other components of the curing agent generate hydration reaction to form hydrated calcium silicate gel, ettringite and other substances to fill the internal pores of soil, making the soil structure denser and greatly improving the strength.

Predicting the emission reduction potential and cost of sustainable aviation fuel (SAF) that aligns with China’s national conditions is essential for advancing the SAF industry and achieving carbon neutrality goals. Based on the principles of international comparability and independent controllability, a lifecycle carbon emission reduction model was developed for two technological pathways: hydroprocessed esters and fatty acids (HEFA) and Fischer-Tropsch (FT). This model forecasted the emission reduction and cost associated with SAF in China’s civil aviation sector from 2025 to 2060.The results indicate that the HEFA pathway, which is suitable for implementation between 2025 and 2030 using waste oils as feedstock, achieves a carbon emissions reduction of 61.3 kgCO_2e/GJ, contributing to an overall reduction of 84.4%. This associated cost ranges from 0 to 1 025.9 CNY/tCO_2e when compared to traditional aviation kerosene. In contrast, the FT pathway-primarily developed between 2030 and 2060 utilizing municipal solid waste as raw material yields the highest carbon emissions reduction at 68.4 kgCO_2e/GJ. Furthermore, routes employing agricultural or municipal solid waste exhibit lower abatement costs than those utilizing forestry waste. Considering China’s specific national conditions, it is determined the FT route utilizing agricultural waste as feedstock is more appropriate for development as the main SAF production technology after 2030 due to its abundant raw materials and comparatively lower abatement costs. Projections suggest that by 2060, reductions in China’s civil aviation SAF could reach approximately 17 177 million tons to 19 819 million tons. From a possible scenario spanning from 2025 to 2060, it is estimated that cumulative carbon abatement costs will amount to between 11 063 to 45 828 billion CNY, this corresponds with a marginal carbon abatement cost ranging from 220 to 697 CNY/tCO_2e.