Abstract:In order to study the shear performance of T-shaped reinforced concrete (RC) beams reinforced by Basalt Fiber Reinforced Polymer (BFRP) grid-Engineered Cementitious Composite (ECC) (hereinafter referred to as BFRP grid-ECC reinforced T-shaped RC beams), the influence of single branch cross-sectional area and ECC thickness on the shear performance of BFRP grid-ECC reinforced T-shaped RC beams was studied by using the finite element analysis software ABAQUS. The results showed that increasing the cross-sectional area of BFRP grid could effectively improve the shear capa-city of beams. In practical engineering, it is recommended to use the BFRP grid with a single branch cross-sectional area of 30 mm², which can make the structure have good bearing capacity and save more materials. Increasing the thickness of ECC could also significantly improve the shear capacity of beams. Finally, based on the truss-arch model, a formula for calculating the shear capacity of BFRP grid-ECC reinforced T-shaped RC beams was established. The deviation between the experimental and calculated values is less than 8%, and the calculated results are in good agreement with the simulated values.

Abstract:Considering three concrete strength grades (C30, C40 and C50) and three GFRP bar dia-meters (8, 12 and 16 mm), 18 GFRP anchors with pre-drilled holes and concrete pull-out specimens were fabricated based on the Embedded Through-Section (ETS) strengthening technique for Fibre Reinforced Plastic (FRP). The central pull-out test was used to study the influence of bar diameter and concrete strength grade on the interface bonding performance of GFRP anchor rods and concrete. Compared with the traditional drilling anchor rod method, this method is easier to operate and avoids the local damage to the concrete caused by drilling. The results show that the bar diameter and concrete strength have significant effects on the bond failure mode, load-slip curve and bond strength. When the interface is debonded, the bond slip curve presents three stages: rising, falling and stable. In case of concrete splitting failure or FRP bar fracture, the bond-slip curve has only an ascending segment. As the concrete strength grade increased from C30 to C50, the bond strength of specimens with diameters of 8 mm and 16 mm is increased by 37.35% and 13.23%, respectively. However, when the bar diameter is 12 mm, with the increase of concrete strength, the failure mode of the specimen changes from GFRP bar fracture to concrete splitting, and the lack of the concrete confinement leads to a significant decrease in the bond strength. With the increase of bar diameter from 8 mm to 16 mm, the increase of bond length leads to the enhancement of the non-uniform distribution of interfacial bond stresses, and the bond strength of C30, C40 and C50 concrete specimens decreases by 40.76%, 47.82% and 51.16%, respectively.

Abstract:In order to study the self-healing behavior of concrete cracks in a chloride environment and its inhibitory effect on chloride ion transport, the dynamic self-healing process of concrete cracks was simulated. The self-healing behavior of concrete under different crack widths and various sodium chloride solutions was analyzed, as well as the inhibitory effect of crack self-healing on chloride ion transport in concrete. The relationship between crack width and sodium chloride solution concentration on crack healing rate was established. The results show that the healing rates of initial cracks with widths of 50, 150, and 250 μm after 60 days in water were 62.1%, 24.4%, and 15.1%, respectively, with the healing rate decreasing as crack width increased. The promoting effect of water on crack healing was limited, as it only effectively healed smaller cracks, generally with widths within 50 μm. The promotion of self-healing for cracks of different widths varied under chloride concentrations of 500, 1 000, and 2 000 mol/m³. When the chloride concentration was relatively low and the crack size was small, chloride ions exhibited a better promotion effect on crack self-healing. After healing for 12 hours in a 400 mol/m³ sodium chloride solution, the initial cracks with a width of 250 μm were completely healed, and the average chloride ion concentration at 5 mm around the cracks decreased by 2.6~5.0 mol/m³.

Abstract:To investigate the mechanical behavior evolution of the reinforced Gabion retaining wall at different heights on slope foundation in the rainy area under the condition of rainfall infiltration during the construction period, a study on the stress and deformation evolution of a reinforced gabion retaining wall with varying height was conducted using field tests and numerical simulations, relying on an actual engineering of the EMU Maintenance Station in the Yichang North Railway Station of the Shanghai-Chongqing-Chengdu High-speed Railway. The research results show that the vertical stress at the base of each level of the double-level and single-level reinforced gabion retaining walls distributes non-linearly along the direction of the geogrid laying during the filling process, but the vertical stress at the base of the upper wall of the double-level retaining wall is less than that of the single-level retaining wall; as the filling height increases, the horizontal earth pressure on the back of each layer of the double-level and single-level retaining walls increases, but the growth rate decreases with the increase in filling height; the strain of the geogrid in each layer of the double-level and single-level retaining walls increases with the increase in filling height, and it is distributed non-linearly along its laying direction, and the strain distribution curve shows a significant peak phenomenon, mainly in the form of single peak and double peaks. The numerical simulation analysis of the deformation of the post-construction double-level and single-level reinforced gabion retaining walls shows that the difference in settlement at the top of the two retaining walls is very small, only 4.24 mm; the overall horizontal deformation of the wall surface is in an outward-inclined form, and the maximum horizontal displacement is 5.42 mm, 2.55 mm, and 5.69 mm respectively, accounting for 0.068%, 0.059%, and 0.071% of the height of this layer of the wall. The horizontal deformation form and size of the wall surface of the upper wall of the double-level retaining wall are relatively consistent with those of the single-level retaining wall.

Abstract:To study the water-salt migration patterns in soil, using sandy loess as the research object, we conducted freeze-thaw, freeze-thaw-evaporation, and freeze-thaw-evaporation-rainfall three types of cycle tests under the conditions of unpressurized supplementation of 0.8% and 1.5% concentration sodium sulfate solution. We explored the water-salt migration patterns of the soil during freeze-thaw, evapo-ration, and rainfall processes, and analyzed the changes in temperature, moisture, and conductivity of the test soil column with respect to the working conditions. The results show that there is a lag phenomenon in the temperature changes of the soil during freeze-thaw cycles, and the amplitude of temperature changes decreases with the increase of soil depth. In all three working conditions, the moisture content and conductivity of the soil show periodic changes. After the freeze-thaw cycle, the water and salt contents of the soil increase. Under evaporation conditions, the salt is transported upward with water and causes oversaturation precipitation at the top of the soil column. Under rainfall conditions, the salt in the upper part of the soil column moves downward with water. Under the same working conditions, a higher concentration of the replenishing solution is more conducive to the accumulation of salt in the upper soil layer. When the unpressurized replenishing solution is 0.8% concentration, the increase in conductivity of the upper part of the soil column in the three working conditions is 0.12, 0.31, and 0.45 dS/m respectively. When the unpressurized replenishing solution is 1.5% concentration, the increase in conductivity of the upper part of the soil column in the three working conditions increases successively to 0.27, 0.36, and 0.52 dS/m. The changes in soil salt content are influenced by the combined effects of temperature, concentration gradient, and action time. Under the freeze-thaw-evaporation-rainfall cycle, the increase in conductivity of the upper soil layer is the greatest.

Abstract:To explore the cumulative damage evolution law and stability characteristics of the surroun-ding rock during the blasting excavation of large-span tunnels, this study used a rock acoustic wave tester and pressure sensors to conduct on-site measurements of the damage characteristics of the surrounding rock and the stress of the initial support structure during the blasting excavation process. Based on the measured results of the surrounding rock damage, the numerical simulation method was used to analyze the stability of the tunnel when there is damage to the surrounding rock. The research results show that the influence depth range of the cyclic blasting excavation on the surrounding rock damage is 3.4 to 3.6 meters; as the test depth increases, the rock wave velocity curve shows an "S" shape distribution, while the cumulative damage curve of the surrounding rock shows an "inverted S" shape distribution; considering the blasting cumulative damage of the tunnel surrounding rock, the rock state in different depth ranges of the test holes varies, that is, the 0.0 to 2.0 meter depth is the loosening zone, the 2.0 to 3.4 meter depth is the moderately damaged zone, and the 3.4 to 4.8 meter depth is the mild damage zone. The numerical simulation results show that compared with the condition without considering the surrounding rock damage, the distribution area of the plastic zone of the surrounding rock under consi-deration of damage is significantly larger; considering the surrounding rock damage, the maximum arch top settlement after tunnel excavation is 24.01 mm (the average value measured on site is 25.8 mm), and the maximum horizontal convergence is 14.39 mm (the average value measured on site is 15.19 mm), while without considering the damage, the maximum arch top settlement is 20.43 mm and the maximum horizontal convergence is 13.85 mm. This indicates that the simulation results considering the surrounding rock damage have a higher degree of consistency with the actual monitoring data.

Abstract:To investigate the vibration effect of the drainage tunnel blasting on the lining structure of the adjacent existing tunnel, the drainage tunnel construction of Beishan No.2 Tunnel in Hao-Ji Railway was considered as the research background. Field monitoring and of dynamic finite element methods were used to analyze the variation laws of peak vibration velocity and stress of the exiting tunnel lining due to the drainage tunnel blasting. The results showed that under the existing blasting scheme, both on-site monitoring and numerical simulation indicated that almost all the peak vibration velocities of tunnel lining were much greater than the allowed vibration velocity of 5 cm/s. The maximum tensile stress was larger than the ultimate tensile strength of the lining concrete, resulting in cracks in the lining; and the blasting of the drainage tunnel has the greatest impact on the side wall of the tunnel facing the vibration source, with a maximum peak vibration velocity of 17.98 cm/s, significantly exceeding the allowed vibration velocity. Based on the Sadovsky's formula fitted from field monitoring data, the maximum charge amount per delay was calculated, and an optimized blasting scheme for the drainage tunnel was proposed. Numerical simulations and on-site monitoring confirmed that the peak vibration velocity of the optimized blasting scheme did not exceed the allowed vibration velocity, thereby ensuring the safety of the tunnel's main lining structure.

Abstract:A regression model was established through orthogonal experimental design and multiple li-near regression methods to analyze the sensitivity of different support stiffness influencing factors and their advantages and disadvantages in terms of supporting stiffness. A first-order regression equation regarding the supporting stiffness was obtained. By adjusting the supporting parameters, the tunnel supporting stiffness was calculated and optimized. Regarding the influence of sprayed concrete thickness, sprayed concrete strength, long anchor rod length, anchor rod circumferential spacing, anchor rod longitudinal spacing, and steel frame longitudinal spacing on supporting stiffness, a first-order orthogonal regression experiment was conducted using the L25(56) orthogonal table, and the constant values of each parameter and the partial correlation coefficients were obtained. A multiple linear regression equation was constructed. Through range analysis and variance analysis, the test results were analyzed using SPSS software, and the remaining influencing factors of supporting stiffness were substituted into the regression equation for verification and analysis. The research results show that the prediction accuracy of this multiple linear regression analysis model is high, with an average relative error of 1.14%. The significant parameters F values of factors such as sprayed concrete strength and sprayed concrete thickness level are greater than F0.001, which play a decisive role in supporting stiffness; the F value of the longitudinal spacing of the steel arch frame is greater than F0.025, and its influence on supporting stiffness is relatively significant; the F values of the circumferential spacing and longitudinal spacing of the anchor rod are greater than F0.1, and these two factors have a generally significant impact on supporting stiffness; the length of the long anchor rod has no significant influence on the value of supporting stiffness.

Abstract:To address the multi-objective optimization problem of construction time, carbon emission and cost in prefabricated building construction, the construction activity process and resource allocation of the standard floor main structure of prefabricated buildings were systematically reviewed. The carbon emission sources and categories in the construction process were identified, and a carbon emission accounting model was constructed by combining the process evaluation method and emission factor method. A carbon emission accounting list was established, and the economic impact of carbon emission was analyzed, providing a basis for construction carbon emission accounting. Considering various resource combination modes of construction activities, the uncertainty of activity time and carbon cost, a discrete multi-objective multi-mode combination optimization model was constructed based on the construction time, carbon emission and cost of each activity under different modes. In response to the characteristics of this optimization model, the non-dominated sorting whale optimization algorithm was discretized. The Pareto solution set of the construction mode combination scheme was obtained through algorithm solution, and the non-dominated schemes were comprehensively ranked using the Analytic Hierarchy Process-improved entropy weight method combined weighted Technique for Order Preference by Similarity to Ideal Solution. This provided a comprehensive ranking for non-dominated schemes, enabling ma-nagers to select the best solution. The application results of engineering examples show that the construction time, carbon emission and cost have been effectively controlled, meeting the expected goals of managers, and verifying the scientific nature of the optimization model and the practicality of the solution method.

Abstract:In order to explore the influence of wind field on the residence time of Gangnan Reservoir, a hydrodynamic and water exchange model of Gangnan Reservoir was established. Set five working conditions of different wind direction , established connectivity matrices for each partition. The results show that the wind field increases the water flow velocity in the whole reservoir area. Under the condition of east, west and north wind, two circulations with different sizes and directions are formed in the reservoir area, and one circulation is mainly in areas II,III,IV and VII, and the other one circulation is mainly in areas IV and X. Under the condition of south wind, four circulations with different sizes and directions are formed in areas II,III and IV. The overall residence time of the reservoir area under windy conditions is larger than that under windless conditions, but the overall residence time is not much different. Furthermore, The influence of wind field on the residence time of main reservoir area and bay area is different. The residence time of main reservoir area increases slightly under the action of wind field, but the residence time of bay area is significantly shortened. The wind field has little effect on the diffusion of Ⅰ to Ⅳ pollutants in the main reservoir area. Wind field has great influence on the diffusion of pollutants in the bay area, which accelerates the diffusion of pollutants in the bay area. The results show that the water diversion under the condition of wind can not only increase the flow velocity, but also increase the connectivity between the water bodies in the reservoir area, especially in the bay area, improve the water exchange capacity and help to improve the water quality.

Abstract:To reveal the displacement response mechanism and stability evolution law of the high slopes on both sides of the Lixian Expressway under seismic action, a systematic investigation was conducted by combining model experiments with theoretical analysis. The focus was on quantifying the displacement characteristics of the high slopes under seismic conditions, and a physical model test platform was established to simulate the dynamic responses of the slopes under different seismic wave parameters (frequency ranging from 10 to 100 Hz, amplitude ranging from 0.05g to 0.60g). The finite element numerical simulation was combined for theoretical verification, and the stability coefficient was calculated using the Mohr-Coulomb criterion. The research process strictly followed the technical route of engineering geo-logical investigation-model construction-loading test-data collection-theoretical analysis, with a particu-lar emphasis on monitoring the displacement time history curves at the top, fault zone, and middle areas of the slopes. The research results show that the top of the slope, lacking lateral constraints, exhibits linear growth characteristics in horizontal displacement under the excitation of seismic waves, and signs of fatigue failure appear after more than 2 000 vibration cycles; the upper edge of the fault zone is the most sensitive to the release of seismic energy, and the displacement accumulation rate is exponentially related to the vibration cycle. The frequency of the seismic waves has a significant impact on the displacement response. The amplitude of the low-frequency band (≤40 Hz) has a larger displacement amplitude but a slower growth rate, while the high-frequency band (>40 Hz) is prone to resonance effects, causing a 15% to 30% increase in displacement. The stability coefficient analysis shows that the relationship between the seismic wave amplitude and the required vibration cycle is a logarithmic function.

Abstract:In order to study the performance characteristics of polyimide-coated Fiber Bragg Grating (FBG) hygrometer, the saturated salt solution was used to control the ambient humidity, and the variation of FBG center wavelength with relative humidity was tested. The effect of temperature on the sensitivity coefficient of humidity was studied, and the simultaneous measurement of temperature and humidity by this hygrometer was achieved. The results showed that: (1) Within the humidity range of 34.7% to 93.1% in the experimental design, the polyimide-coated FBG humidity meter had a good response to humidity changes. During the humidification and dehumidification processes, the center wavelength exhibited a clear linear relationship with relative humidity, and the humidity sensitivity coefficient ranged from 5.1 to 15.7 pm/%. (2) The thicker the polyimide coating, the higher the humidity sensitivity, and the linear correlation degree between the center wavelength and relative humidity was also higher. (3) Taking the humidity meters No.2 and No.4 as examples, the relative errors of the humidity sensitivity coefficients of the two humidity meters due to a 20 ℃ temperature change were 4.82% and 3.11% respectively. The influence of temperature on the humidity sensitivity coefficient was very small, and its effect on the humidity sensitivity coefficient can be ignored when the temperature change was not significant in actual measurement. (4) Taking the humidity meters No.2 and No.4 as examples, the tempe-rature sensitivity coefficient and humidity sensitivity coefficient were obtained through indoor experiments, and a mathematical matrix for simultaneously measuring temperature and humidity was established, enabling the FBG humidity meter to achieve simultaneous measurement of environmental temperature and humidity.

Abstract:To address the challenges of strong dependence on large-scale labeled data, insufficient feature representation, and single-granularity segmentation results in retinal fundus image segmentation, an unsupervised multi-granularity segmentation method for retinal images is proposed. A novel fully convolutional encoder-decoder architecture was designed to effectively capture local details and global semantic features of images, achieving efficient reconstruction of multi-level representations. On this basis, a comprehensive loss function was constructed by integrating pixel-level patch contrastive loss, representation-level contrastive learning loss, and global reconstruction loss. This joint optimization constrained the model across multiple feature scales, enhancing the representation capability and aligning the feature space with the structural distribution of the segmentation task. Subsequently, a diffusion-condensation algorithm was applied within the representation space to aggregate multi-scale semantic information, improving boundary precision and structural coherence, and generating segmentation results with hierarchical and multi-granular characteristics. Experiments conducted on publicly available retinal fundus datasets demonstrated that the proposed method achieved a 3.7% improvement in Dice coefficient compared with state-of-the-art unsupervised segmentation approaches, showing superior performance in both detail fidelity and structural consistency. The results indicated that this method enabled accurate and multi-granularity segmentation of retinal fundus images.