Search Results (1,041)

It is essential to elucidate the shear mechanical behavior of structural planes to assess the risk to rock masses and protect them from shear failure. Current research on shear mechanical behavior is focused on isotropic structural planes with the same lithology on both sides. However, anisotropic structural planes, commonly found in nature, may exhibit unique mechanical behavior that differs from isotropic structural planes. Therefore, it is necessary to study the factors affecting the shear strength of the anisotropic structural planes. In this paper, the direct shear numerical tests on anisotropic structural planes were carried out using the three-dimensional distinct element code (3DEC) based on the laboratory test. The numerical test results illustrate that the error between the peak shear strength of the numerical test and the laboratory test is basically within 10%. The shear stress-displacement curves of the numerical and laboratory tests are similar, which verifies the accuracy of the numerical test. According to the Barton standard sections, anisotropic structural plane models with different roughness and size were established, and the direct shear numerical tests with different normal stresses were carried out. To predict the peak shear strength of the anisotropic structural planes, one hundred and eighty-one sets of direct shear numerical test data were selected. Normal stress, roughness, compressive strength of soft and hard rock masses, basic friction angle of soft and hard rock masses, and structural plane size were used as input parameters to establish a back propagation (BP) neural network model. The research results show that, under identical conditions, the shear strength of the anisotropic structural planes decreases as the structural plane size increases. On the contrary, the shear strength increases with the increasing structural plane roughness and normal stress. For the BP neural network prediction model, the root mean square error (RMSE) and coefficient of determination (R²) of the training set are 0.441 and 0.957. For the test set, the RMSE is 0.489, and R² is 0.947, which indicates that the predicted values are in good agreement with the actual values. Full article

This study explores the water inrush phenomenon and its control measures during tunnel construction in enclosed karst geological conditions through a real case study. Using numerical simulation methods, the study investigates the variations in water level drawdown, drainage volume, and the changes in principal stress and displacement at four locations (arch waist, left arch waist, left arch foot, and arch bottom) during tunnel construction under three excavation methods (full-face excavation method (FFEM,), bench excavation method (BEM), and reserved core soil excavation method (RCSEM)), six water head heights (122 m, 162 m, 202 m, 242 m, 282 m, 322 m), and five excavation advances (0.5 m, 1.0 m, 1.5 m, 2.0 m, 2.5 m). The results show that, compared to controlling excavation advance, water level drawdown and drainage volume are more sensitive to increases in initial water head height. The reserved core soil method results in the smallest drainage volume and water level drawdown, effectively controlling stress increase and significantly mitigating arch bottom uplift. The RCSEM has the smallest drainage volume, making it an ideal choice for ecological protection. Full article

The inhomogeneous distribution of temperature in bridges causes stresses and strains inside the structure, thus affecting the safety and durability of bridges. Therefore, the study of temperature action in bridge structures is crucial; boundary conditions of the temperature field are critical to study them. In this study, the calculation method of the boundary conditions for the three-dimensional temperature field of box girders in the natural environment is investigated by taking box girders as the object, which integrates the solar radiation, environmental radiation, structural shading effect, and convective heat transfer between the inner and outer surfaces of box girders. The effects of the atmospheric transparency coefficient and concrete short-wave absorptivity on the temperature field distribution of box girders were also investigated. It is shown that the calculation results obtained by the method in this study are in good agreement with the measured results, and the method can effectively simulate the three-dimensional temperature field of the box girder. The atmospheric transparency coefficient and the short-wave absorptivity of concrete have a significant effect on the temperature field distribution of box girders, and materials with lower short-wave absorptivity can be used in the design of box girders to reduce the structural temperature. Full article

In order to advocate for green and environmentally friendly travel modes, enhance the attractiveness of rail transit, and promote the sustainable development of rail transport, we focus on the transportation organization problem under limited-resource conditions. This paper studies the formulation of a train plan under the condition of through operation between intercity and high-speed railway, constructing a multi-objective nonlinear optimization model with train frequency, a stop plan, and turn-back station locations as decision variables. Given the high dimensionality of model variables and complex constraints, an improved multi-population genetic algorithm (IMGA) is designed. Through an actual case study of the through operation between the Chengdu–Mianyang–Leshan Intercity Railway and the Chengdu–Chongqing High-Speed Railway, a staged solution method is adopted for analysis. The results indicate that the through-operation mode can save operational costs for enterprises and travel costs for passengers, while also better adapting to changes in passenger flow. Additionally, the IMGA demonstrates better solution quality and higher efficiency compared to the classical genetic algorithm. The main contribution of this paper is to propose a novel approach to solve the train plan problem. It also contributes to creating a high-quality, high-efficiency, and high-comfort integrated transportation service network, promoting the sustainable development of rail transit. Full article

Weakly supervised crack segmentation aims to create pixel-level crack masks with minimal human annotation, which often only differentiate between crack and normal no-crack patches. This task is crucial for assessing structural integrity and safety in real-world industrial applications, where manually labeling the location of cracks at the pixel level is both labor-intensive and impractical. Addressing the challenges of labeling uncertainty, this paper presents CrackCLIP, a novel approach that leverages language prompts to augment the semantic context and employs the Contrastive Language–Image Pre-Training (CLIP) model to enhance weakly supervised crack segmentation. Initially, a gradient-based class activation map is used to generate pixel-level coarse pseudo-labels from a trained crack patch classifier. The estimated coarse pseudo-labels are utilized to fine-tune additional linear adapters, which are integrated into the frozen image encoders of CLIP to adapt the CLIP model to the specialized task of crack segmentation. Moreover, specific textual prompts are crafted for crack characteristics, which are input into the frozen text encoder of CLIP to extract features encapsulating the semantic essence of the cracks. The final crack segmentation is determined by comparing the similarity between text prompt features and visual patch token features. Comparative experiments on the Crack500, CFD, and DeepCrack datasets demonstrate that the proposed framework outperforms existing weakly supervised crack segmentation methods, and the pre-trained vision-language model exhibits strong potential for crack feature learning, thereby enhancing the overall performance and generalization capabilities of the proposed framework. Full article

Cement–asphalt (CA) mortar voids in earth’s structure are prone to inducing abnormal vibrations in vehicle and track systems and are more difficult to recognize. In this paper, a vehicle–ballastless track coupling model considering cement–asphalt mortar voids is established and the accuracy of the model is verified. There are two main novel results: (1) The displacement of the track slab in the ballastless track structure is more sensitive to the void length. Voids can lead to blocked vibration transmission between the ballastless track slab and concrete base. (2) The wheel–rail vibration acceleration is particularly sensitive to voids in cement–asphalt mortar, making the bogie pendant acceleration a key indicator for detecting such voids through amplitude changes. Additionally, the train body pendant acceleration provides valuable feedback on the cyclic characteristics associated with single-point damage in the cement–asphalt mortar, thereby enhancing the accuracy of dynamic inspections for vehicles. In the sensitivity ordering of the identification indexes of voids, the bogie’s vertical acceleration in high-speed trains > the nodding acceleration of the bogie > the vehicle’s vertical acceleration. Adaptive suspension parameters can be designed to accommodate changes in track stiffness. Full article

The unit slab track structure in high-speed railways exhibits multiple periodic characteristics, which result in bandgaps of elastic wave propagation within the track structure. Moreover, local defects inevitably occur in the ballastless track structure, disrupting its periodicity and leading to the generation of defect states. An analytical model for infinite periodic slab track structure was established using the Floquet transform and supercell method, accounting for local defects, to clarify the propagation of flexural waves in slab tracks. The formation mechanism of elastic wave bandgaps in periodic slab tracks can be explained by Bragg scattering and local resonance. In the low-frequency below 200 Hz, the local resonances of the slab interact with the flexural waves in the rail, forming an approximately broad coupling bandgap. The bandgaps expand significantly with the increasing fastening stiffness. Besides, when the stiffness of the isolating layer beneath the slab is within the range of 0.9 to 1.0 × 10⁹ N/m³, a broad coupled bandgap is generated in the frequency range of 180–230 Hz. Local damage caused by contact loss between the composite slab and baseplate leads to defect states, and the frequencies of the defect states correspond to unique wave modes, demonstrating the localization of elastic waves near the defect location. The formation mechanism of defect states can be elucidated by the local resonance of the structure at the defect. The frequency of the first-order defect state is significantly affected by the defect size, the second-order defect state exhibits unidirectional propagation characteristics, and the third-order defect state shows localized vibration characteristics, which can provide a reference for defect identification. Full article

A 27.5 kV cable is one of the important infrastructures of a high-speed railway traction power supply system, and the reliability of the cable directly affects the stability and safety of the high-speed railway power supply. The cable runs in the complex environment of the laying site and will inevitably face the influence of electrical stress and thermal stress, resulting in air gap and insulation deterioration, which poses a threat to the safety of a high-speed railway traction power supply system. In this paper, an electric–thermal coupling model is built and simulated under normal operating conditions and different cable damage conditions. The distributions of the electric field and thermal field under different conditions of cables are explored. The weak points of a cable with poor heat resistance and easily produced air gaps are found. The influence of various temperature differences on a damaged air gap inside the cable is studied. Finally, the damage mechanism of a further increase in the cable’s air gap caused by partial discharge of the air gap is proven. This study provides a theoretical basis for inhibiting cable degradation and prolonging cable life. Full article

Geopolymer, as a promising inorganic binding material, holds potential for use in constructing base layers for highway pavements. This study aims to evaluate the mechanical properties of geopolymer-stabilized macadam (GSM) at both the micro- and macro-scale by a series of tests, demonstrating that high-Ca GSM is a high-quality material for pavement base layers. The results demonstrated that GSM exhibits outstanding mechanical and fatigue properties, significantly surpassing those of cement-stabilized macadam (CSM). Performance improvements were particularly notable with higher binder-to-aggregate ratios. GSM derived from a high-Ca precursor achieved a relatively higher fatigue life and resistance to permanent deformation under cyclic loading, outperforming CSM. Furthermore, relationship models developed from the indirect tensile fatigue test results provide a valuable framework for evaluating GSM’s long-term road performance. Microstructural analyses revealed that geopolymer features a reticulated gel structure and a denser, more continuous internal matrix, which contribute to its superior properties. The interface products of GSM, including C–A–S–H gel and C(N)–A–S–H gel, enhance mechanical interlocking and promote early strength development, accounting for its exceptional mechanical strength and fatigue resistance. These findings offer valuable insights and technical guidance for employing geopolymer as a sustainable and effective alternative to cement-stabilized macadam in base layer construction. Full article

High-speed rail (HSR) environments present unique challenges due to their high mobility and dense passenger traffic, resulting in dynamic and unpredictable task generation patterns. Mobile Edge Computing (MEC) has emerged as a transformative paradigm to address these challenges by deploying computation resources closer to end-users. However, the limited resources of MEC servers necessitate efficient task partitioning, wherein a single task is divided into multiple sub-tasks for parallel processing across MEC servers. In the context of HSR environments, the task partitioning ratio is pivotal in ensuring quality of service (QoS) and optimizing resource utilization, particularly under dynamic and high-demand conditions. This paper proposes a deep reinforcement learning (DRL)-based task partitioning mechanism using Twin Delayed Deep Deterministic Policy Gradient (TD3) for HSR environments with MEC servers (MECSs). The proposed method dynamically adjusts task partitioning ratios by leveraging real-time information about task characteristics and server load conditions. The experimental results show that when the task arrival rate is 20, the delay is improved by about 5% compared to random and about 13% compared to no_partition. When it is 50, there is no significant difference from random and about 2% improvement compared to no_partition. The task throughput is almost the same when it is 20. However, when it is 50, random is much better. We also looked at the performance change according to the number of serving MECSs. In this process, we can also note the research direction of finding an appropriate number of serving MECSs K. The results highlight the efficacy of DRL-based approaches in dynamically adapting to the unique characteristics of HSR environments, achieving optimal resource allocation and maintaining high QoS. This paper contributes to advancing task partitioning strategies for HSR systems and lays the groundwork for future research in MEC-based HSR systems. Full article

Train-induced environmental vibrations are a common issue in urban rail transit systems, particularly in suburban railways operating at high speeds, where the impact of these vibrations is more pronounced. This presents significant challenges for urban planners and engineers. Existing research has mainly focused on the impact of single tunnel structures on ground vibrations, with limited understanding of the vibration propagation characteristics of adjacent bidirectional tunnels. To address this gap in knowledge, this study investigates the ground vibration attenuation characteristics induced by train operations in the underground sections of suburban railways, with a focus on the amplification effects of adjacent tunnels on ground vibrations. The results show that the vibrations induced by the trains are concentrated in the 20–50 Hz frequency range and exhibit similar characteristics in all directions. The maximum vertical vibration acceleration and peak acceleration occur directly above the train tunnel. Additionally, adjacent tunnels significantly amplify the maximum peak acceleration at measurement points in directions perpendicular to the track, including both horizontal and vertical directions. Furthermore, the soil within the adjacent tunnels also exhibits amplification of the vertical power spectral amplitude in the 40–100 Hz frequency range. The findings of this study provide new insights into the influence of adjacent bidirectional tunnels on environmental vibrations in suburban railway operations. These results are of significant importance for optimizing railway design and vibration mitigation measures. Full article

High-speed railways are critical infrastructure in many countries, but their construction generates substantial spoil, particularly in mountainous regions dominated by tunnels and slopes, necessitating the establishment and monitoring of spoil disposal areas. Inadequate monitoring of spoil disposal areas can lead to significant environmental issues, including soil erosion and geological hazards such as landslides and debris flows, while also hindering the recycling and reuse of construction spoil, thereby impeding the achievement of circular economy and sustainable development goals for high-speed railways. Although the potential of geographic information systems, remote sensing, and global positioning systems in waste monitoring is increasingly recognized, there remains a critical research gap in their application to spoil disposal areas monitoring within high-speed railway projects. This study proposes an innovative framework integrating geographic information systems, remote sensing, and global positioning systems for monitoring spoil disposal areas during high-speed railway construction across three key scenarios: identification of disturbance boundaries (scenario 1), extraction of soil and water conservation measures (scenario 2), and estimation of spoil volume changes (scenario 3). In scenario 1, disturbance boundaries were identified using Gaofen-1 satellite data through processes such as imagery fusion, unsupervised classification, and spatial analysis. In scenario 2, unmanned aerial vehicle data were employed to extract soil and water conservation measures via visual interpretation and overlay analysis. In scenario 3, Sentinel-1 data were used to analyze elevation changes through the differential interferometric synthetic aperture radar method, followed by the estimation of spoil volume changes. The effectiveness of this integrated framework was validated through a case study. The results demonstrate that the framework can accurately delineate disturbance boundaries, efficiently extract soil and water conservation measures, and estimate dynamic changes in spoil volume with an acceptable error margin (15.5%). These findings highlight the framework’s capability to enhance monitoring accuracy and efficiency. By integrating multi-source data, this framework provides robust support for sustainable resource management, reduces the environmental impact, and advances circular economy practices. This study contributes to the efficient utilization of construction spoil and the sustainable development of high-speed railway projects. Full article

The subgrade structure of high-speed railways is an important foundation for the safe and smooth operation of high-speed trains, and the scientific design of the subgrade structure provides a fundamental guarantee of its durability and technical economy. As, in the development of high-speed railways in China, higher speeds are being pursued, more requirements have been put forward for the dynamic stability of subgrade structures. To address this issue, this article focuses on the control requirements for the long-term stability of subgrade deformation, and various design methods for high-speed railway subgrade structures are presented. Considering the energy dissipation and dynamic stability characteristics of subgrade filling materials, the dynamic performance of coarse-grained soil filling materials in the bottom layer and graded crushed stones in the surface layer are revealed. The methods for determining the values of dynamic parameters such as the dynamic modulus and damping ratio are provided. Based on the dynamic shakedown theory, the stress–strain hysteresis characteristics of fillers and the variation law of dissipated energy are revealed. The correlation between unit volume dissipated energy and shakedown state under cyclic loading conditions is identified. A criterion for determining the critical shakedown state of high-speed railway subgrade structures based on equivalent unit volume dissipated energy is proposed, and a method for determining the design threshold of dynamic stress and dynamic strain is also proposed. The results show that the shakedown design critical values of equivalent unit volume dissipated energy in the bottom and surface layers of the foundation were between 0.0103~0.0133 kJ/m³ and 0.0121~0.0149 kJ/m³, respectively. The critical dynamic strain range was 0.8 × 10⁻³~1.3 × 10⁻³. On this basis, a high-speed railway subgrade design method based on energy dissipation and dynamic shakedown characteristics was developed. The results can provide theoretical support for the design of high-speed railway subgrade structures with different filling material alternatives and control standards. Full article

The effects of high-temperature modified phosphogypsum (HPG), incorporated at contents of 40%, 50%, and 60%, on the compressive strength and elastic modulus of mortar and concrete were investigated. Additionally, the influence of graded granulated blast furnace slag powder (GGBS), quicklime, and silica fume on the mechanical properties of HPG-based mortar (HPGM) and HPG-based concrete (HPGC) was discussed. Moreover, the microstructure of HPGM was analyzed using scanning electron microscopy (SEM). A two-dimensional mesoscale model of HPGC was developed to predict how variations in HPG content, coarse aggregate characteristics, and interfacial transition zone (ITZ) characteristics influence the compressive strength and elastic modulus of HPGC. The experimental results showed that high volumes of HPG weakened the mechanical properties of HPGM and HPGC, while appropriate amounts of mineral admixtures offset the negative effects caused by calcium hydroxide (Ca(OH)₂) crystals and impurities within the system. The simulation results indicated that the maximum deviation between the mesoscale model prediction and experimental data was only 8.38%, which verified the accuracy of the mesoscale model prediction. The compressive strength of HPGC initially decreased and subsequently increased with the rise in the modulus and content of coarse aggregate, whereas it declined with higher HPG dosage and increased ITZ thickness. In contrast, the elastic modulus of HPGC showed a gradual increase with rising coarse aggregate content and improved ITZ mechanical properties, while it decreased as HPG content and ITZ thickness increased. Full article