Abstract:

Current studies on the thermal effect on the full-range debonding process of Carbon Fiber Reinforced Polymer (CFRP)-steel interfaces are rare and fail to account for residual interfacial friction stress. Therefore, this paper proposes an analytical approach to evaluate the debonding response of CFRP-strengthened steel interfaces under combined thermal and mechanical loads, accounting for interfacial friction stress. Based on the trilinear interfacial bond-slip constitutive model, the full-range debonding process for CFRP-steel interfaces was analyzed and the analytical expressions for the interfacial load-slip response, interfacial shear stress distribution, CFRP normal stress and the interfacial debonding ultimate bearing capacity were derived and verified through experiments. The results show that the proposed method can model the interfacial debonding process of CFRP-steel interfaces under the influence of temperature variation with reasonable accuracy, and that the thermal effects on the debon-ding behavior are significant and the degree of influence depends on the temperature difference and bond length.

Abstract:

In order to improve the utilization rate of coal gangue and reduce the harm caused by coal gangue accumulation, the feasibility of using coal gangue as filler in reinforced soil retaining wall projects and the influence of different reinforcement parameters on retaining walls were explored. Through model tests, the stress and deformation laws of retaining walls under different reinforcement lengths (0.66H, 0.99H, 1.31H, where H is the wall height) and different reinforcement strengths (10 kN/m, 20 kN/m, 30 kN/m) were studied. The results show that when the retaining wall is subjected to a load, the deformation of wall surface increases gradually from bottom to top, while the vertical additional stress and the reinforcement strain show a unimodal distribution, with the peak point located directly below the load. Increasing the reinforcement length has a significant effect on limiting the lateral displacement of wall surface and the settlement at the top of the wall. Increasing the reinforcement strength is conducive to enhancing the diffusion effect of the vertical stress. Overall, under a vertical load of 70 kPa, the maximum displacement of wall surface of the geogrid-reinforced coal gangue retaining wall is 0.1%H, the settlement at the top of the wall is 0.27%H to 0.45%H, and the reinforcement strain is less than 0.12%, where the geogrid and the coal gangue achieves a good interaction, and the whole wall is in a stable state. In practical engineering, it is recommended that the length of the reinforcement be no less than 0.5H.

Abstract:

To clarify the influence of sand incorporation on the evaporation cracking behavior of clayey soils, indoor experiments were conducted to simulate arid environments to induce the development of desiccation cracks in clay samples. Quantitative analysis of the formed cracks was performed using digi-tal image processing techniques. Based on the staged morphological characteristics of crack evolution, a classification nomenclature system for soil desiccation cracks was established. The present study investigated the effects of temperature (40 to 60 ℃), sand content (0% to 30%), and sand particle size (0 to 2.0 mm) on clay desiccation cracks. The experimental results demonstrate that: (1) Desiccation crack development in sandy clay progresses through three distinct stages: formation, development, and stabilization. Sand particles reduce the rate of moisture evaporation in clay, thereby diminishing fluctuations in the surface stress field and decelerating the crack initiation and development. Sand particles exhibit inferior water-holding capacity compared to clay particles, leading to the preferential formation of cracks at the interfaces between sand particles and clay particles. (2) Incorporating sand into the clay matrix significantly suppresses crack development, with this effect strengthening as the sand content increases. The crack-suppressing efficacy of sand particles exhibits a first increasing then decreasing trend as the particle size increases, with an optimal particle size range (0.5 to 1.0 mm) determined under the experimental conditions. Furthermore, the crack-suppressing effect of sand particles amplifies with rising temperatures.

Abstract:

To mitigate the threat of permafrost slope hazards to transportation engineering in high-altitude regions, and reveal the slope instability mechanisms under freeze-thaw cycles, six covered slopes in western Sichuan are taken as research objects. Based on the hydrothermal coupling theory, freeze-thaw cycle simulation considering diurnal temperature variation in winter is carried out for the six slopes using COMSOL Multiphysics numerical simulation software, and the spatio-temporal variation of hydrothermal field is analyzed. The failure modes of slope are summarized, and the positional relationship between the freeze-thaw interface and the sliding surface is found. The results show that the freeze-thaw cycles mainly affect the soil in the shallow layer of frozen soil slopes. After the slopes are subjected to several freeze-thaw cycles, the moisture content of the soil in a certain depth range is higher than those in other depths, and a water-gathering zone is formed in the slope. Five kinds of slope failure modes are identified from the six covered slopes, which are slope shallow melt soil collapse, slope shallow melt soil creep, slope shallow melt soil extrusion, convex slope shallow melt soil collapse and concave slope shallow melt soil collapse. Under freeze-thaw cycles, the freeze-thaw interface of covered slope is located deeper than the sliding surface.

Abstract:

To further investigate the reinforcement effects of high-strength geotextiles in high-fill steep slopes, model tests were conducted to compare high-strength geotextiles with other different geosynthetic materials including common geotextiles and geogrids. The results indicated that high-strength geotextile-reinforced steep slopes showed better performance in reducing slope body settlement, lateral displacement, and additional vertical stress compared with those reinforced with common geotextiles and geogrids. At the same time, the influence of different laying methods of high-strength geotextile on the stress and deformation characteristics of the slope body was studied. The results showed that changing the laying methods of high-strength geotextiles could enhance the safety and stability of high-fill loess steep slopes. Among the five different laying methods, the reinforced laying method of digging two grooves downwards and laying geotextiles (concave×2) can effectively reduce the crest settlement and additional vertical stress of the reinforced steep slopes. The research results can provide a reference for the engineering application of high-strength geotextile-reinforced steep slopes.

Abstract:

To solve the aerodynamic effects of road tunnel caused by high-speed trains passing through tunnels, this paper proposes a new type of discontinuous buffer structure. In the current research on buffer structures, no research has been conducted on the length ratio of buffer sections and the discontinuous buffer structure. Based on the ^κ-ε two-equation turbulence model, the dynamic mesh technology provided by Ansys Fluent software is used to simulate the entire process of high-speed trains passing through buffer structures and tunnels at a speed of 350 km/h. By optimizing variables such as the discontinuity distance a of the buffer structure, the length L_i of each buffer section, the cross-sectional area A_i, and the number of buffer sections n, a discontinuous buffer structure that can effectively mitigate pressure gradient peaks is designed. The calculation results show that when these variables are set as a=0.50 m, L₁∶L₂∶L₃=1∶1∶1, A₁=A₂=A₃=150 m² and n=3, the pressure gradient reduction effect is the best, reaching 44.04%.

Abstract:

In order to study the influence of a rectangular tunnel undercrossing construction on the deformation of the existing tunnel, a semi-analytical solution for the rectangular tunnel undercrossing the existing tunnel is proposed. Firstly, based on the characteristics of the convergence deformation of the section after the excavation of the rectangular tunnel, the law of the ground deformation induced is derived by using the random medium theory. The existing tunnel is regarded as an Euler-Bernoulli beam on the Kerr foundation model. Consequently, the differential equation of longitudinal force equilibrium of the existing tunnel is obtained, and the finite difference method is used to obtain the calculation method of the stress and deformation of the existing tunnel caused by the undercrossing rectangular tunnel excavation. By comparing with the experimental values of the indoor model, the accuracy of the calculation results in this paper is verified. Finally, the influence of key parameters such as rectangular tunnel width, tunnel depth, internal friction angle of soil, bending stiffness of the existing tunnel and ground loss rate is analyzed. The results show that the increase of half-width and ground loss rate of the rectangular tunnel leads to the linear increase of vertical deformation of the existing tunnel. The decrease of the tunnel depth leads to a significant increase in the vertical peak deformation of the existing tunnel, but narrows the influence range on the tunnel settlement. The increase of the internal friction angle of soil leads to a significant increase in the vertical deformation of the existing tunnel and a slight decrease in the tunnel deformation trough. With the increase of the bending stiffness of the existing tunnel, the vertical deformation of tunnel is significantly reduced.

Abstract:

In order to study the relaxation law of the contact stress of sealing gaskets under long-term compression, the thermal-oxidative aging tests of the sealing gasket at different temperatures were carried out. ABAQUS software was used to establish a three-dimensional compression numerical model of the sealing gasket, so as to analyze the stress distribution inside the sealing gasket and predict the ser-vice life of the sealing gasket based on the test data and the time-temperature superposition principle. The research shows that the performance retention rate of the sealing gasket gradually decreases and tends to be stable with increasing aging time, while decreases with increasing aging temperature. With the increase of compression, holes tend to form at both ends of the sealing gasket due to warping, and the greater the compression, the larger the holes. Therefore, on the premise of meeting the waterproof requirements, the appropriate reduction of compression is conducive to improving the waterproof performance of the sealing gasket. The contact stress between the sealing groove and the sealing gasket is overall higher than that between the sealing gaskets. According to the calculations based on the time-temperature superposition principle, the compression of sealing gasket by 9 mm can meets the 100-year waterproof requirement of a certain subway Line 1. The present research is of great significance for improving the operational capacity of a certain subway Line 1.

Abstract:

Spatial narrative theory is widely used in industrial heritage renewal, but there are fewer researches on the development of spatial narrative strategies using quantitative evaluation methods. For this reason, taking Tianjin No.1 Machine Tool Works as an example, based on the two analytical methods of AHP-entropy method and GIS suitability evaluation, the suitability evaluation system of spatial narrative is studied, and on this basis, the narrative strategies are developed. The narrative elements of the Machine Tool Works are divided into 4 guideline-level indicators and 12 factor-level indicators, and all these indicators are classified into 5 grades. The weights for indicators are calculated by AHP-entropy method, and the spatial narrative suitability of the factor-level indicators is quantitatively analyzed using GIS. Based on the suitability analysis results of the factor-level indicators and the weights calculated by the AHP-entropy method, the distribution characteristics of spatial narrative suitability of the Machine Tool Works are obtained through GIS multi-criteria overlay analysis. The results show that there are 8 zones most suitable for narrative development in the Machine Tool Works in total, which are mainly concentrated on the south side of the Machine Tool Works, accounting for 13.9% of the total area. Based on the analysis results, a renewed method for the Machine Tool Works is proposed in terms of narrative themes and sequences, including five themes: beginning, construction, innovation, prosperity, and transformation. According to the themes and the locations of suitable narrative zones, 1 narrative core, 2 narrative clusters, and 13 narrative points are set up, and an elevated industrial corridor is utilized to connect all the most suitable narrative zones.

Abstract:

To improve low-amplitude structural reservoir trap identification and reservoir prediction accuracy, a new method of constructing low-frequency model combining constrained relative acoustic impedance with geostatistics is put forward. In this method, relative acoustic impedance information is extracted from seismic data and used as a constraint for the low-frequency model. By employing geostatistical methods such as Kriging interpolation and sequential Gaussian simulation interpolation optimization is performed based on the spatial correlation and variation characteristics of geological parameters. A low-frequency model is subsequently constructed and used for inversion research. The effectiveness of this method is demonstrated through its application in an actual work area. The results show that, compared with traditional methods, the low-frequency model constructed in this study has significant advantages in matching well logging data, depicting structural morphology, and predicting reservoir development. Its agreement with the actual geological conditions is over 85%. Moreover, the present study also reveals the limitations of this method. For example, due to the influence of seismic data resolution, the prediction accuracy for thin layers needs to be improved.

Abstract:

Taking the northern slope of the Tianshan Mountains in Xinjiang as the study area, high-precision snow cover data at specific time benchmarks were generated based on the Landsat time-series sa-tellite images and the SNOMAP snow mapping algorithm. These data were used as "ground truth" to evaluate the data accuracy of three MODIS snow products: MODIS daily cloud-free snow cover 500 m product for China, MODIS daily cloud-free snow product for Northern Hemisphere, and MODIS snow cover index and phenology product for High Mountain Asia. Based on the evaluation results, the MODIS snow product with the highest accuracy was selected to analyze the snow cover frequency and its spatiotemporal variation characteristics in the region from 2001 to 2020. The results showed that: (1) The MODIS snow cover index and phenology product for High Mountain Asia had the highest accuracy, outperforming the other two products in terms of overall accuracy, underestimation error, snow classification accuracy, and Kappa coefficient; (2) The Intra-annual snow cover fraction in the northern slope of the Tianshan Mountains showed periodic changes, with peaks occurring from December to January of the following year and troughs occurring from June to August. The snow cover rate in areas above 4 500 meters above sea level was almost 100% in every month of the year; (3) The spatial distribution of the multi-year average snow cover frequency showed significant differences, with obvious east-west variations, which increased with rising altitude. The snow end date was significantly advanced in the eastern plains and near the Tianshan Mountains, highlighting the impact of climate warming on snow phenology.

Abstract:

Aiming at the problem of weak fault signals of magnetic coupler bearings and the difficulty of feature extraction, which leads to the low accuracy of fault classification, a rolling bearing fault diagnosis method is proposed, which uses improved beluga whale optimization (IBWO) to optimize variational mode decomposition (VMD), and combines the hybrid model of convolutional neural network (CNN) and bidirectional long short-term memory (BiLSTM). Firstly, the IBWO algorithm is used to optimize the two key parameters of VMD (mode number K and penalty factor α). Then, the two optimized parameters are substituted into VMD to obtain K intrinsic mode functions (IMFs). Next, the IMF component with the minimum envelope entropy is selected as the effective IMF component, which is finally input into the CNN-BiLSTM model for fault diagnosis. Experiments are conducted using the public datasets from the Case Western Reserve University and the University of Ottawa, respectively. The results show that the fault identification accuracy of the proposed model can reach more than 95%, which proves that the present diagnosis method has a significant advantage in identification accuracy. The research results can provide a reference for the fault diagnosis of magnetic coupler bearings.