Zelin Zhou

Understanding the long-term creep behavior of sandstone after high-temperature treatment is crucial for the stability control of underground engineering subjected to thermal effects, such as deep geothermal development and nuclear waste storage. In this study, uniaxial and triaxial creep experiments were conducted on sandstone samples heat-treated at 800 °C, during which acoustic emission (AE) signals were continuously monitored. Based on the AE count evolution, a nonlinear creep damage constitutive model was developed. The finite difference form of the model was derived and implemented into FLAC ^3D via a user-defined constitutive routine. The proposed model was validated against experimental creep curves, demonstrating superior fitting accuracy compared with the improved Nishihara model. Using the established numerical approach, the instantaneous deformation of surrounding rock during tunnel excavation and the time-dependent creep behavior after excavation were systematically investigated. The damage and deformation evolution of the surrounding rock under unsupported and supported conditions were compared. Results indicate that applying shotcrete and anchor rod support reduces roof displacement by 76.4%, floor displacement by 34.2%, and sidewall displacement by 35.7% compared with the unsupported case. Moreover, the maximum principal stress increases and the stress concentration zone shifts closer to the tunnel surface under supported conditions. The proposed model effectively captures the accelerated creep stage and provides a reliable tool for evaluating long-term stability of tunnels in high-temperature rock masses.

Water inrush disasters in karst tunnels pose a significant threat to construction safety, project timelines, and the long-term sustainability of infrastructure. Effective risk assessment is crucial for mitigating these hazards and ensuring the resilient development of underground transportation networks. This study proposes a quantitative risk assessment model that integrates the entropy weight method with attribute interval recognition theory to address the uncertainties inherent in complex geological environments. First, a hierarchical evaluation index system is established based on four primary controlling factors: stratigraphy, geological structure, topography, and hydrogeology. Subsequently, the entropy weight method is employed to objectively determine the weight of each index, thereby minimizing human bias. The attribute interval recognition model is applied to calculate the comprehensive attribute measure for each tunnel segment, effectively managing the fuzziness of risk classification boundaries. The risk grade is ultimately determined using the confidence criterion. The proposed model is applied to the Qigan Mountain karst tunnel in Chongqing, China, which is divided into 56 segments for detailed analysis. Results show 41.32% (4088 m) high-risk, 40.14% (3971 m) medium-risk and 18.55% (1835 m) low-risk sections, which are highly consistent with the theoretical water inflow calculation results. The model realizes accurate and quantitative water inrush risk assessment, providing a scientific basis for disaster prevention and control in karst tunnel construction, and further promoting the sustainability and safety of underground engineering in karst areas.

The construction of intersection tunnels in urban induces multiple stress redistribution in the surrounding rock, leading to engineering disasters such as instability in rock strata during excavation, disturbance of supporting structures in existing tunnels, and subsidence of ground adjacent buildings. Employing an appropriate construction method is crucial in circumventing excessive stress concentrations and large-scale rock strata subsidence, making it a key aspect of urban intersection tunnel engineering. In this paper, a numerical model for an urban intersection tunnel is developed based on an underground circular road project in a central business district. We conduct numerical simulations of the excavation processes using the full-section method, step method, and center cross diagram (CRD) method, respectively. The findings indicate that while different construction methods do not change the variation trends of surrounding rock stress and displacement, adjacent ground building deformation, and existing tunnel convergence, they affect the variation degrees. The maximum compressive and tensile stresses in the surrounding rock caused by the CRD method are the smallest, which are 3.56 MPa and 0.76 MPa, respectively. The maximum arch subsidence affected the amount, and horizontal convergence affected the amount of branch tunnel #1 caused by the CRD method are the smallest too, which respectively are 1.428 mm and 0.931 mm. The foundation subsidence and overall inclination of the ground building resulting from the three methods are identical. Then, we discuss the construction safety of the three methods and obtain the influence order on construction stability, which is as follows: full-section method > step method > CRD method. It is concluded that the CRD method is the most suitable for urban intersection tunnel engineering in terms of safety. This study could offer valuable insights for selecting construction methods in urban intersection tunnel engineering and provide a foundation for evaluating the safety and stability of tunnel construction.

The surrounding rock and high water pressure in weak watery strata have adverse effects on the mechanical properties of tunnel support structures. In order to optimize the anti-drainage design of tunnels in weak watery strata and evaluate their structural safety, this paper relies on the Taidacun Tunnel of the China–Laos Railway to carry out field monitoring research. A dual-field fluid–solid coupling calculation model is established to optimize the tunnel’s waterproof and drainage design, combined with a bending moment curvature model to evaluate structural safety. The main conclusions are as follows: Under the action of high water and soil pressure, the structural safety margin of the water-rich fine sand section of the Taidacun Tunnel is small, and waterproof and drainage design optimization is required. Combined with the proposed average pressure reduction coefficient, the influence of the water level and annular blind pipe spacing on the water pressure of the lining is proved, and then the optimal annular blind pipe spacing in the water-rich area of the tunnel is determined. A structural safety evaluation method based on the bending moment curvature model is proposed. Two models of elastic beam and moment–curvature beam are used to analyze the mechanical characteristics and optimization effects of the structure under optimal annular blind pipe spacing.

A geostress field continuously evolves with long-term tectonic activity. A fault, as a general product of tectonic movements, has a great influence on the geostress field in the vicinity. To analyze the geostress field characteristics and influencing factors near the fault fracture zone in high-altitude areas, this study takes the Dianda-Piru fault on the Qinghai–Tibet Plateau as its research object. Based on the geological conditions and in situ stress measurement data in the study area, a refined numerical model was established using numerical simulation to invert the geostress field in the vicinity of the fault fracture zone, and a quantitative analysis of the factors influencing the geostress distribution was carried out. The results show that the overall relationship between large horizontal principal stress σ_H, vertical stress σ_v, and small horizontal principal stress σ_h is σ_H > σ_v > σ_h, and the surrounding rock stress is dominated by horizontal stress. Geostress is released within the fault fracture zone to a certain extent, and there is a certain degree of stress concentration within the intact rock mass on the upper plate of the fault. The elastic modulus has a greater influence on the geostress field near the fracture structure area than Poisson’s ratio, and the range of the stress-weakening zone increases with the decrease in the elastic modulus. The maximum principal stress inside the fault increases with the increase in the angle between the fault strike and regional principal stress, while the deflection angle of the surrounding principal stress direction decreases with the increase in this angle. The study of the distribution law of geostress fields with developed fracture structures can provide theoretical guidance for the sustainable development of engineering construction in tectonically active areas.

As an important part of road transportation, bridge engineering plays a pivotal role in infrastructure construction. The wind field characteristics of the bridge site area have an essential influence on both the construction and operation period of the bridge, especially in mountainous canyon terrain. In this paper, a numerical simulation using computational fluid dynamics software was conducted to examine the intricate wind field characteristics in mountainous regions. The study focused on ideal V-shaped and U-shaped canyons, aiming to investigate the influence of various parameters. These parameters included three distinct heights, seven angles, and seven widths of the canyon. The findings indicate that in both ideal V-shaped and U-shaped canyons, the canyon acceleration effect weakens as the angles or widths of the canyon increase. The wind speed amplification effect gradually disappears when the V-shaped canyon angle exceeds 160° or when the U-shaped canyon has a width-to-height ratio of approximately 5:1. The wind speed amplification effect strengthens as the canyon height increases. The wind speed acceleration effect exhibits a linear relationship with the angle of the V-shaped canyon, while it demonstrates a logarithmic relationship with the width of the U-shaped canyon. Additionally, the wind speed amplification factor follows a logarithmic distribution along the canyon height. The wind field characteristics observed in this study offer valuable insights for future bridge designs in mountainous regions featuring V-shaped and U-shaped canyons.

This paper is a contribution to analyzing the aerodynamic forces on a streamlined box girder (SBG) with coupled vibration in a potential flow. The key enabling step was to assume that the normal velocity of the airflow at an arbitrary point on the surface of the SBG was equal to the normal velocity of the surface motion. The aerodynamic drag force, lift force, and pitching moment were expressed as functions of the motion state of the SBG and the SBG’s shape-related parameters. To investigate the applicability of this force model, the analytical solution at various angles of attack was compared with a numerical simulation in a viscous flow. The results imply that the amplitude of the analytical lift force and pitching moment agree well with the numerical results under the angles of attack of 0° and ±3°. Furthermore, the analytical drag force effectively predicts the second-order phenomenon resulting from the multiplication of the vertical and torsional vibration velocities. As a consequence, the present analytical solution provides an effective method for analyzing the aerodynamic forces acting on SBGs with coupled vibration.