Search Results (31)

The artificial ground freezing method (AGF) is widely used in underground construction to reinforce the ground and ensure construction safety. This study systematically evaluates the implementation of the artificial ground freezing method in the construction of a metro tunnel cross-passage, with a focus on analyzing the soil’s thermo-mechanical behavior and assessing safety performance throughout the construction process. A combined approach integrating field monitoring and refined three-dimensional numerical simulation using FLAC3D is adopted, considering critical factors, such as freezing pipe inclination, thermo-mechanical coupling, and ice–water phase transitions. Both field data and simulation results demonstrate that increasing the density of freezing pipes accelerates temperature reduction and intensifies frost heave-induced displacements near the pipes. After 45 days of active freezing, the freezing curtain reaches a thickness of 3.7 m with an average temperature below −10 °C. Extending the freezing duration beyond this period yields negligible improvement in curtain performance. Frost heave deformation develops rapidly during the initial phase and stabilizes after approximately 25 days, with maximum vertical displacements reaching 12 cm. Significant stress concentrations occur in the soil adjacent to the freezing pipes, with shield tunnel segments experiencing up to 5 MPa of stress. Thaw settlement is primarily concentrated in areas previously affected by frost heave, with a maximum settlement of 3 cm. Even after 45 days of natural thawing, a frozen curtain approximately 3.3 m thick remains intact, maintaining sufficient structural strength. The refined numerical model accurately captures the mechanical response of soil during the freezing and thawing processes under realistic engineering conditions, with field monitoring data validating its effectiveness. This research provides valuable guidance for managing construction risks and ensuring safety in similar cross-passage and cross-river tunnel projects, with broader implications for underground engineering requiring precise control of frost heave and thaw settlement. Full article

When the shield machines are constructed in soft soil, excavation may be impeded by the accumulation of cutter head mud. Geological conditions and shield construction are identified as the main factors for cutter head mud formation, based on analysis of its mechanism. In addition to traditional metrics, the imperforation area in the cutter head center is incorporated into the analysis of shield construction factors. The Analytic Hierarchy Process (AHP) is utilized to establish a risk assessment model for shield cutter head mud cake, determining the weight of each sub-factor and enabling a preliminary risk assessment of mud cake occurrence. This study applies Analytic Hierarchy Process (AHP) to classify the factors affecting shield mud by using the Mawan cross-sea channel construction project (Moon Bay Avenue along the Yangtze River) as a case study. Each factor is scored and weighted according to established scoring criteria and evaluation formulas, and then the results of the risk of shield mud cake in the Mawan tunnel are obtained. Moreover, field observations validate the proposed risk model, with the derived risk index demonstrating strong alignment with actual data. Full article

During the construction of a large immersed tunnel crossing an ultra-wide inland river, the long drying time after the excavation of the foundation trench and changes in river flow velocity result in the river carrying a large amount of sediment into the foundation trench and the slope, increasing installation difficulties and threatening construction safety. This study investigates the back-silting characteristics and their impacts on foundation trench slope stability during an ultra-wide immersed tunnel excavation at LunGui Road in Foshan City, China. Numerical simulations reveal the spatiotemporal distribution patterns of deposited sediments at the trench bottom and side slopes, with distinct behaviors identified between the flood season and dry season. Siltation predominantly occurs at the trench bottom, with deposition thickness decreasing almost linearly from the bottom to the slope crest. Hydroperiod variations considerably influence the spatiotemporal distribution of back-silting. Then, the Morgenstern–Price method was employed to analyze slope stability under varying back-silting and dredging conditions, quantifying the relationship between safety factor and sediment thickness. Furthermore, the evolution of critical failure surfaces and the safety factor under different dredging strategies was systematically examined. The critical values of back-silting thickness corresponding to different dredging slope ratios are provided. The research findings provide valuable insights for formulating engineering strategies for trench excavation of extra-wide immersed tube tunnels in inland waterways. Full article

Line 9 of the Barcelona Metro crosses beneath the Llobregat and Besòs Rivers, requiring tunneling through soft deltaic deposits of Holocene age. The excavation was carried out using Earth Pressure Balance (EPB) Tunnel Boring Machines (TBMs), a method commonly employed in urban environments to control ground movements and minimize settlements. This study analyzes the ground response to EPB tunneling, focusing on key factors such as TBM operational parameters (face pressure, shield pressure, etc.), grouting techniques, and the influence of shaft entry/exit points, hyperbaric stops, tool wear, and the learning curve. Additionally, secondary influences, including variations in cover depth and the presence of lightly compacted made ground, were found to exacerbate ground movements. Field data collected from Section 1 of Line 9 provide a detailed assessment of settlement patterns and ground behavior. Results indicate that, while EPB TBMs generally maintain ground stability with minimal settlement (with average volume losses below 0.5%), certain site-specific challenges, such as inconsistent grouting and shaft transitions, led to localized volume losses and settlement. This paper contributes to refining predictive models of ground–structure interaction in soft ground tunneling, offering insights to optimize future EPB operations in similar geological conditions, ensuring more effective control over ground movements and settlement mitigation. Full article

As a long lifeline system of buried structures, the utility tunnel (UT) is vulnerable to earthquake invasion. For utility tunnels with inverted siphon arrangements crossing rivers, the seismic response is more complex due to the basin effect of acceleration in the topography and the influence of fluctuating hydrodynamic pressure, but there is currently a gap in targeted seismic response analyses and references. Based on a UT project in Haikou, this paper studied seismic responses of a cast-in-place UT considering the coupled model of water–soil–tunnel structure on ABAQUS software. Herein, the dynamic fluctuation of hydrodynamic pressure is simulated using an acoustic–solid interaction model. A viscoelastic artificial boundary was used to simulate the soil boundary effect, and seismic loads were equivalent to nodal forces. Considering seismic invading direction and varying water elevation, this paper investigates the dynamic response characteristics and damage mechanisms of river-crossing utility tunnels. This study shows that the basin effect causes the soil acceleration around the UT to show variability in different sections, and the amplification factor of the peak acceleration at the central location is almost doubled. The damage and dynamic water pressure of the UT are intensified under bidirectional seismic excitation, and the damage location is concentrated at the junction of the horizontal section and the vertical section. Bending moments and axial forces are the main mechanical behaviors along the axial direction. Changes in river levels have a certain positive effect on the UT peak MISES, DAMAGEC, and SDEG, and it exhibits a certain degree of energy dissipation and seismic damping effect. For the aseismic design of cross-river cast-in-place utility tunnels, bidirectional seismic calculations should be performed, and the influence of river hydrodynamic pressure should not be neglected. Full article

Artificial objects, particularly tunnels used for water transport under pressure, impact the geological and hydrogeological environment to a greater or lesser extent, and it is vital to assess their contributions to groundwater quality. Although tunnels are typically lined with concrete, their interaction with the hydrogeological environment intensifies over time. In this study, the detailed spatiotemporal monitoring of all hydrogeological features within the potential influence zone of the hydraulic tunnel of the Pirot Hydropower Plant has been conducted in order to determine the degree of interaction between the artificial object and the natural environment in real time, and to assess the correlation between monitored parameters. Natural conditions of the environment were defined, as well as potential changes through the observing groundwater regimes. The monitoring network included observations of groundwater regimes at seven springs located in close proximity to the hydraulic tunnel, within the tunnel, at three piezometers, and along the river, while methods employed were hydrological monitoring, physicochemical monitoring, and groundwater piezometer sensing. Cross-correlation analysis has been applied for assessing the impact of precipitation dynamics on the spring discharge regime. The results indicate a direct influence of the tunnel on the hydrogeological environment, proving the consistency and high correlation between the monitored parameters. Full article

Asymmetrical V-shaped tunnels often appear in tunnels crossing the river or urban underground road tunnels. The smoke flow inside is affected by a lot of factors. A full understanding of the smoke flow in this kind of tunnel is the basis of the smoke control. In this study, the effects of slope composition and fire heat release rate (HRR) on the longitudinal induced airflow velocity, the smoke back-layering length at the small slope side, and the maximum ceiling temperature were studied by the numerical method. The results show that when the fire occurs at the slope change point of the V-shaped tunnel, the maximum ceiling temperature decreases with the increase in the slope of the large-slope side tunnel. The longitudinally induced velocity is primarily related to the slope of the large-slope side tunnel and the fire HRR. When the slope difference between the side tunnels or the slope of the large-slope side tunnel is large, the smoke in the small-slope side tunnel flows back toward the fire source after reaching its maximum dispersion distance and then reaches a quasi-steady state. The smoke back-layering length is mainly affected by the slope and length of the large-slope side tunnel. When the slope of the large-slope side tunnel is 9%, the induced airflow velocity from the small-slope side can prevent the spread of smoke. The empirical models of the smoke back-layering length and the longitudinal induced airflow velocity in the small-slope side tunnel are drawn, respectively, by the theoretical analysis and the numerical results. This study can provide technical support for the design and operation of smoke control systems in V-shaped tunnels. Full article

Shield tunnels’ structural stability is challenged due to the fact that they are often built under rivers, lakes, and oceans. It is crucial to execute the structural deformation perception of the shield tunnel. Fiber Bragg grating (FBG) sensing technology is sensitive to deformation information, making it one of the greatest options for shield tunnels to perceive structural deformation. In this study, a 1:20 scale model test was carried out to investigate the deformation perception of the shield tunnel structure under three different layouts of surface-mounted FBG sensors. The deformation law of the tunnel is discussed, under the condition of two-factor cross fusion and especially under the condition of constant water pressure and soil pressure change. The results indicate that, under the combined action of water and soil pressure, the uniform water pressure of 0.33 MPa has a stabilizing effect on the segment strain under the vertical load of 0.4 MPa. The traditional four-point layout and the 18° uniform layout are more effective in detecting changes in local tunnel curvature and strain, respectively, compared to the 36° uniform layout mode. It is advised that the traditional four-point layout be used to collect information for other sections’ monitoring and that the 18° uniform layout is for harsh terrain conditions. Full article

As urbanization progresses and city populations grow, river-crossing tunnels assume a crucial role in transportation networks, with the maximum scour depth constituting a critical parameter influencing tunnel safety. Using Line 6 of the Nanning Metro in Guangxi, China as a case study, a two-dimensional hydrosediment mathematical model was employed to investigate variations in maximum bedrock scouring. This study introduces the concept of critical frequency floods and compares it with urban flood control standards to determine the appropriate flood frequency for calculating maximum bedrock scour depth. The impact of bed sediment particle size on maximum scour depth is quantified, revealing a decrease in scour depth of 0.3 to 0.6 m for every 1 mm increase in particle size. The relationship between bed sedimentation and the Froude number demonstrates an upward-opening parabolic symmetry: lower Froude numbers correspond to relatively stable beds, while higher numbers correlate with an increased amplitude of bed erosion or deposition. The curve’s nadir identifies the critical threshold of the Froude number, facilitating calculation of the channel’s critical water depth. In practical engineering applications, a bed under conditions of critical water depth tends to be more stable, thereby favoring the selection of sites for river-crossing tunnels. Full article

The construction of multiple tunnels across inland rivers has had a significant influence on the improvement of the transportation infrastructure. The technology for constructing tunnels is progressing towards the development of larger cross-sections, longer distances, and the ability to withstand high hydraulic pressure in complex hydrogeological conditions, including high-permeability strata. In order to ensure the face stability of shield tunnels under high hydraulic pressure that crosses a fault fracture zone, it is necessary to study the progressive failure mechanism of shield tunnel faces induced by high hydraulic pressure seepage. This paper employs finite element numerical simulation software to methodically examine the variation in the characteristics of the water seepage field, limiting support force, and face stability failure mode of shield tunnels passing through fault fracture zones with high hydraulic pressure under varying fault fracture width zones. The results show that the formation hydraulic gradient will progressively widen when the tunnel face is located within the undisturbed rock mass and is advanced towards the area of fault fracture. This will raise the likelihood of instability in the shield tunnel and progressively raise the limiting support force on the tunnel face. Moreover, as the tunnel face nears the region of fault fracture within the undisturbed rock mass, the damage range increases gradually. In addition, due to the increase in seepage force, the angle between the failure area and the horizontal plane becomes more and more gentle. On the contrary, as the tunnel’s face moves closer to the undisturbed rock mass from the region of the fault fracture, the damage range gradually decreases, and the dip angle between the damage area and the horizontal plane becomes steeper and steeper due to the decreasing seepage force in the process. The study findings presented in this work are highly significant, both theoretically and practically, for the design and management of safety. Full article

The study of shield tunnel segment flotation is crucial for controlling the precision of underground excavation projects. Based on Winkler’s beam foundation theory, the load structure method, and the equivalent continuous beam model, and by considering the mechanical and spatial conditions that cause segment flotation, a novel theoretical calculation method for cumulative flotation is proposed using a simplified equivalent stiffness model of the tunnel. Additionally, a new concept of “equivalent flotation force” is introduced. The rationality and applicability of this theoretical calculation method are verified by comparing it with on-site construction data from the Yuanjiang River Crossing Tunnel Project in Changde, Hunan Province, China. The experimental results demonstrate that the theoretical calculation closely approximates the surface deformation monitoring data of the tunnel alignment in the eastern section of the project, and their deformation patterns are similar. Near the starting shaft, there is significant settlement influenced by stratum loss due to smaller tunnel flotation, with greater settlement occurring in the upper part. However, at approximately 45 m into both sections, they enter a deformation stability zone showing significant correlation in longitudinal deformation. Through comparison and verification of on-site experiments and theoretical model analysis, we preliminarily elucidate the feasibility of this innovative cumulative flotation theoretical calculation method which provides an important theoretical basis for assessing segment flotation issues in subsequent tunnel shield construction evaluations. Full article

This paper proposes a scale model test to simulate shield tunnel excavation over long distances. The test simulates the whole process of shield tunneling through the Weihe River on Xi’an Metro Line 1, where the tunneling length and diameter reach 100 m and 6 m, respectively. The dimensions of the test setup were 6.0 m × 1.0 m × 1.0 m, the diameter of the tunnel model was 160 mm, and the geometric similarity ratio was 1:40. Finite element analysis and field measurements were performed to complement the test results. By comparing the finite element simulation and field measurement, the scale model test was validated and verified to be reliable. The results show that the test effectively predicts riverbed deformation caused by shield construction. In addition, it can be applied to soil stability analysis and the impact evaluation of surface deformation in other shield-crossing rivers, complex strata, and superstructure groups, providing auxiliary guidance for shield constructions. Full article

This article combines numerical simulation and field monitoring methods to study the stability of the overlying Liuyang River embankment in the tunnel crossing between Huaqiao Station and Rice Museum Station of Changsha Metro’s Line 6. Using AutoCAD, 3Dmine, and COMSOL Multiphysics, a calculation model of the entire subway tunnel section crossing the flood control embankment under the coupling of fluids and solids was established. The process of tunnel-crossing the embankment and the variation in spatial displacement and plastic strain in different geological layers were analyzed from the perspective of time evolution and spatial distribution. The research results show that during the process of crossing the embankment, the deformation of the east bank is greater than that of the west bank, and crossing the west bank is the relatively riskier stage of the entire project. Moreover, during the process of crossing the embankment, the overlying soil layer will produce a plastic strain zone, and only a small amount of plastic strain is generated in the surrounding sandstone layer of the tunnel walls. In terms of the magnitude of plastic strain, the plastic strain area produced by the leading tunnel’s surrounding rocks is larger than that of the following tunnel. As the excavation progresses, a funnel-shaped settlement displacement gradually forms during the passage of the leading tunnel, and this settlement funnel gradually expands during the passage of the following tunnel, with the maximum settlement point transitioning from directly above the leading tunnel to the middle position between the two tunnels. Using the jitter filter algorithm and the adjacent average method to process the field monitoring data, the results show that the monitored deformation results well match the simulated settlement results. Full article

Tunnels play a vital role in enhancing traffic flow and supporting public transportation systems. However, the discharge of polluted air and waste heat from vehicles passing through tunnels significantly raises the temperature inside, presenting challenges in terms of occupant comfort, tunnel safety, and infrastructure integrity. Therefore, ensuring proper temperature control is essential for their efficient operation. This study aims to investigate the phenomenon of temperature rise in ultra-long tunnels during normal operations, as limited research has been conducted in this area. The Shanghai Yangtze River Tunnel serves as a case study, utilizing temperature and air velocity data collected throughout the year (2021) from the management company. The analysis reveals that the temperature distribution near the tunnel exit is influenced by outdoor temperature fluctuations and traffic volume. The highest temperatures occur on 25 August (39.74 °C) during peak traffic hours. On-site measurements of tunnel temperature, humidity, and air velocity during winter and summer seasons yield the following results. During winter, the air temperature and wall temperature inside the tunnel experience significant increases along its length. The air temperature rises by approximately 11 °C from the entrance to the exit, while the wall temperature increases by about 15 °C. In contrast, during summer, the air temperature only rises by 2.7 °C, and the wall temperature increases by around 3 °C. Consequently, the humidity decreases along the tunnel, and this decrease is correlated with the magnitude of temperature increase. Furthermore, measurements of air velocity indicate that natural and traffic-induced winds contribute to the overall airflow inside the tunnel. A temperature data logger installed in the tunnel recorded temperature changes during the period of pandemic lockdown and subsequent recovery, spanning the spring and summer seasons. During the lockdown period, there was a relatively small increase in temperature along the tunnel, suggesting that vehicle heat dissipation is the primary factor contributing to temperature rise inside. Additionally, a method is proposed to predict the cross-sectional temperature of the tunnel using measured air velocities. Full article

Underwater shield tunneling will disturb the soil near the river, especially in water-rich soft ground. This may cause a groundwater infiltration hydraulic gradient to exceed the critical value, leading to calamities, such as unexpected flooding or submerged erosion. To ensure the security of construction and the stability of river embankment seepage, it is crucial to assess the safety of the underwater tunnel cover thickness. A shield tunnel project under a river in Hefei is used as an example. The numerical model established by the finite element method is used for calculating and analyzing the changes in the groundwater flow field and the stability state of embankment seepage induced by underwater shield tunneling under different overburden thickness conditions. The results show that the construction disturbance of the shield tunnel through the river is increased, the internal force environment of the embankment slope is destroyed, and the maximum seepage hydraulic gradient is increased. In the case study, the embankment keeps in a stable state of seepage when the cover thickness of the shield tunnel has 2.9 times its outer diameter. The findings of this study can serve as a scientific guide to assure seepage stability in an underwater shield tunneling project and to stop river embankment erosion. Full article