Search Results (6)

The stress distribution after excavation becomes highly complex in large-span bifurcated tunnel sections commonly found in urban underground interchanges. This study investigates the stress evolution induced by the excavation of large-span and bifurcated tunnel, focusing on the 32.17 m maximum-span section of the Shenzhen Baopeng–Shahe Underground Interchange. The results show that stress concentration near the tunnel walls of large-span sections is greater than that in sections with bifurcated tunnels. Adjusting the burial depth of the large-span tunnel, the influence of stiff layer thickness on the redistribution of surrounding rock stress was analyzed. When the tunnel is buried at a shallow depth and the stiff layer thickness is small, the maximum tangential stress of the surrounding rock occurs at the stiff layer boundary, and the surrounding rock remains entirely elastic. In large-span tunnels, as the thickness of the stiff layer increases from 5 m to 20 m, the stress relaxation zone grows from 0 m to 8 m, and the stress-bearing zone expands from 10 m to 27 m. As the burial depth increases and the stiff layer thickness grows, the maximum tangential stress shifts to within the stiff layer. In this case, the tangential stress distribution at the stiff layer boundary becomes non-smooth. Therefore, an appropriate stiff layer thickness must be selected to prevent the surrounding rock from entering a plastic state. The findings provide theoretical guidance and technical support for the design of large-scale underground interchange bifurcated tunnels, advancing the intelligent and scientific development of urban underground transportation facilities and offering significant practical and social benefits. Full article

Accurate cost estimation during the conceptual and feasibility phase of highway projects is essential for informed decision making by public contracting authorities. Existing approaches often rely on pavement cross-section descriptors, general project classifications, or quantity estimates of major work categories that are not reliably available at the early planning stage, while focusing on one or more key asset categories such as roadworks, bridges or tunnels. This study makes a novel contribution to both scientific literature and practice by proposing the first early-stage highway construction cost estimation model that explicitly incorporates roadworks, interchanges, tunnels and bridges, using only readily available or easily derived geometric characteristics. A comprehensive and practical approach was adopted by developing and comparing models across multiple machine learning (ML) methods, including Multilayer Perceptron-Artificial Neural Network (MLP-ANN), Radial Basis Function-Artificial Neural Network (RBF-ANN), Multiple Linear Regression (MLR), Random Forests (RF), Support Vector Regression (SVR), XGBoost Technique, and K-Nearest Neighbors (KNN). Results demonstrate that the MLR model based on six independent variables—mainline length, service road length, number of interchanges, total area of structures, tunnel length, and number of culverts—consistently outperformed more complex alternatives. The full MLR model, including its coefficients and standardized parameters, is provided, enabling direct replication and immediate use by contracting authorities, hence supporting more informed decisions on project funding and procurement. Full article

Middle rock pillars (MRPs) play a crucial role in the stability of bifurcated small clear-distance tunnels. Assessing the stability of the MRP is a key challenge in design and construction. This study focuses on the bifurcated small clear-distance section of the Xiamen Haicang Shugang evacuation channel underground interchange tunnels. The stability criteria for the MRP during both the early design and later construction stages were analyzed by using the strength reduction method (SRM) via numerical simulations. In the design stage, the SRM was applied to determine the stability limit state of the MRP. Relationships between rock mass density, cohesion, and elastic modulus were identified, and these parameters were combined with basic cohesion values for an initial stability assessment. During the construction stage, the full excavation process was analyzed by examining the distribution and changes in the plastic zone of the rock mass. Two key construction stages, a 10 m excavation on the main line upper step and a 10 m excavation on the ramp upper step, were identified as points where the plastic zone of the MRP began to form on the sidewall and the center, respectively. Multiple linear regression was used to determine the displacement, stress, and plasticity criteria for MRP stability. A comprehensive criteria formula incorporating the width–span ratio, tunnel vault settlement, and horizontal clearance convergence was developed, providing technical guidance and a scientific basis for similar projects. Full article

Tunnel-interchange sections are characterized by complex driving tasks and frequent traffic conflicts, posing substantial challenges to overall safety and efficiency. Enhancing safety in these areas is crucial for the sustainability of traffic systems. This study applies behavior adaptation theory as an integrated framework to examine the impact of environmental stimuli on driving behavior and conflict risk in small-spaced sections. Through driving simulation, 19 observation indicators are collected, covering eye-tracking, heart rate, subjective workload, driving performance, and conflict risk. The analysis, using single-factor ranking (Shapley Additive Explanation), interaction effects (dependence plots), and multi-factor analysis (Structural Equation Modeling), demonstrates that driving workload and performance dominate the fully mediating effects between external factors and conflict risk. High-load environmental stimuli, such as narrow spacing (≤500 m) and overloaded signage information (>6 units), significantly elevate drivers’ stress responses and impair visual acuity, thereby increasing task difficulty and conflict risk. Critical factors like saccade size, heart rate variability, lane deviation, and headway distance emerge as vital indicators for monitoring and supporting driving decisions. These findings provide valuable insights for the operational management of small-spacing sections and enhance the understanding of driving safety in these areas from a human factor perspective. Full article

Tunnel–interchange connecting sections pose significant safety challenges on mountainous expressways due to their high incidence of accidents. Improving road safety necessitates a comprehensive understanding of driver behavior in such areas. This study explores the influences of road characteristics, signage information volume, and traffic conditions on drivers’ car-following and lane-changing behavior in tunnel–interchange diverging areas. Utilizing driving data from 25 subjects of 72 simulated road models, driving performance is assessed using the Friedman rank test and multivariate variance analysis. The results highlight the significant influence of both connection distance and signage information load on driving behavior. In tunnel–interchange scenarios, the reduction in velocity increased by 62.61%, and speed variability surged by 61.11%, indicating potential adverse effects on driving stability due to the environmental transitions. Decreased connection distances are associated with reduced lane-changing durations, larger steering angles, and increased failure rates. Furthermore, every two units of increase in signage information leads to a 13.16% rise in maximum deceleration and a 5% increase in time headway. Notably, the signage information volume shows a significant interaction with connection distance (F > 1.60, p < 0.045) for most car-following indicators. Hence, the study recommends a maximum connection distance of 700 m and signage information not exceeding nine units for optimal safety and stability. Full article

Close excavation section spacing, the mutual influence and interpenetration of various processes, and the multiple disturbances of the middle rock pillar in a small clear-distance tunnel pose great difficulty to construction. This study adopted the small clear-distance tunnel of Xiamen Haicang Evacuate Channel as the research object. The tunnel belonged to a small clear-distance tunnel in an urban super large and complex underground interchange hub where complex adjacent small clear-distance tunnels were adopted. ABAQUS was used to analyze the influence of different excavation schemes, lithological grades, and footage lengths for tunnel stability. The deformation and stress characteristics of the tunnel’s surrounding rock and lining structure in different excavation schemes (full section method, bench method, center diaphragm (CD) method, and double wall heading method), lithological grades (III, IV and V), and footage lengths (3 m, 4 m and 5 m) were introduced. The results showed that the double wall heading method could effectively control the horizontal displacement of the hance, and the overall stress state of the lining in the CD and double wall heading methods were reasonable. The vertical displacement of the surface and vault was positively correlated with the elastic modulus of the rock mass. When no temporary support was present in the grade V rock mass, the area from the hance to the arch foot was prone to large deformation. Reducing the footage was beneficial to controlling the deformation of the vault and hance. This study can provide a reference for the on-site construction of small clear-distance tunnels. Full article