Search Results (589)

Uniform and energy-efficient brick cooling is important for product quality, heat recovery, and tunnel-kiln performance. This study examines how vertical heat-source placement affects airflow, convective heat transfer, heated-surface temperature uniformity, pressure loss, and ideal air-side pumping demand in a 1:4-scale tunnel-kiln cooling-zone model. A three-dimensional CFD model was validated against published Nusselt-number measurements over Re = 15,938–30,890. The predicted average Nusselt numbers showed a mean absolute deviation of 6.55%. All configurations contained four complete thermally active brick units: two longitudinal sources (H1–H2) and two transverse sources (H3–H4). In Setting 1, the longitudinal and transverse sources occupied layers 3 and 2, respectively; in Setting 2, they occupied layers 1 and 2; and in Setting 3, layers 3 and 4. The configurations were compared over setting-specific Reynolds numbers of 16,829–30,641 while maintaining identical brick geometry, source number, and total imposed thermal input. Source placement affected thermal performance mainly by changing the exposure of heated surfaces to established high-velocity passages and wake regions. Setting 3 produced the highest average Nusselt number at the lowest and highest operating points, whereas Setting 1 was marginally higher at two intermediate points. At the highest point, where inlet velocities differed by less than 0.6%, Setting 3 increased the average Nusselt number by approximately 7–8% relative to Setting 2 while requiring about 4.5% less ideal pumping power. Under the investigated scaled, steady forced-convection conditions, Setting 3 provided the most favorable combined performance in terms of convective heat transfer, heated-surface temperature uniformity, and ideal air-side pumping demand. Full article

Under high-density urban underground development conditions, excavation of a large-section tunnel overcrossing an existing tunnel with ultra-small clearance may induce unloading-induced rebound of the underlying ground, thereby causing uplift deformation of the existing tunnel. Three-dimensional finite element analysis and field monitoring were conducted to compare the deformation-control performance of different control-measure combinations and to assess the sensitivity of key parameters of the bench-beam uplift-resistant system. The results showed that, under the basic structural condition of the composite three-layer lining system, the combined control scheme limited the maximum uplift of the existing tunnel to 4.71 mm, corresponding to a reduction of 33.10% relative to the baseline condition. However, compared with the bench-beam uplift-resistant system alone, the addition of surface pre-grouting produced only a further reduction of 0.10 mm, indicating a relatively limited incremental contribution to uplift control under the investigated conditions. Among the parameters considered, pile length exerted the greatest influence on the uplift response of the existing tunnel, followed by pile diameter and the equivalent stiffness of the pipe-jacking capping beam, whereas the number of section-steel members had the smallest influence. When the pile tip extended to approximately 0.5D below the invert of the existing shield tunnel, where D denotes the outer diameter of the existing tunnel, the marginal benefit of further increasing pile length gradually diminished. Field monitoring further revealed a spatially non-uniform vertical deformation response of the existing tunnel after implementation of the comprehensive control scheme. The measured deformation trends and response characteristics were generally consistent with the numerical results. These findings provide a useful reference for the selection of deformation-control measures and the design of uplift-resistant structural parameters in similar large-section tunnel overcrossing projects with ultra-small clearance. Full article

In situ-reconstruction and expansion of existing tunnels in complex urban areas involve simultaneous construction and traffic operation, while pre-existing structural defects may further amplify deformation and safety risks under excavation disturbance. To address this issue, this study develops a dynamic deformation-risk assessment framework for the traffic-bearing side of reconstructed tunnels by integrating defect-induced structural deterioration, excavation-stage deformation responses, and cloud-model-based uncertainty characterization. A three-dimensional finite-difference model was established for an in situ-tunnel reconstruction project in China, in which an elastic modulus weakening coefficient was introduced to represent the mechanical deterioration associated with existing defects. Field monitoring was used to validate the numerical model. At an excavation advance of 47.0 m, the measured and simulated crown settlements were 2.40 and 2.73 mm, respectively, with a relative deviation of 13.75%, while differences at more than 80% of the excavation nodes were within 1 mm. The dynamic assessment showed that the membership degrees of crown settlement and clearance convergence to Grade 2 were 0.418 and 0.406, respectively, with neither indicator entering the Grade 4–5 high-risk range. Clearance convergence entered Grade 2 earlier during excavation and was therefore identified as a priority monitoring indicator for subsequent construction. Numerical simulation was used to obtain and validate the excavation-induced deformation responses, whereas the cloud model was used to classify the corresponding dynamic risk state; no independent long-term deformation forecasting was performed in this study. Full article

Long-distance free-surface water-conveyance tunnels require a spatially continuous representation of transient water depth, yet in practice flow is monitored at only a few sections. This study develops a physics-informed neural network (PINN) that reconstructs the transient water-depth field of unsteady free-surface flow in such tunnels from two- or three-point sensors. The one-dimensional Saint-Venant equations, closed with a Darcy–Weisbach steady friction term in hydraulic-radius form, are embedded as a soft constraint in the training loss, so that sparse depth observations are combined with the governing conservation laws to recover the field at unobserved interior and downstream locations. High-resolution finite-volume (FVM) solutions of a 500 m circular tunnel under a flood-rise scenario provide the reference data. The PINN reduces the relative L₂ error at unobserved sections to approximately one-quarter of that of an otherwise identical, physics-free ANN (2.50% versus 10.05% at an interior section; 4.77% versus 13.69% at an extrapolation section). Runs repeated with different random seeds confirm statistical stability at zero noise, while revealing that a minority of trainings at 10% noise converge to spurious solutions. Sensor-placement experiments, including layouts anchored at the true domain boundaries (x = 0 and 500 m), show that boundary anchoring—particularly of the upstream boundary—governs both accuracy and noise robustness: boundary-anchored two-sensor layouts remain accurate in most runs under 10–20% observation noise, whereas interior-only layouts degrade sharply. The method is presented as an offline reconstruction tool; its extension to streaming data assimilation is discussed as future work. Full article

This study investigates the stability of three-dimensional (3D) tunnel roofs with varied burial depth in saturated rock strata following the Hoek–Brown (HB) failure criterion. Within the framework of limit analysis, a 3D kinematic collapse mechanism for tunnel roofs, incorporating the existence of pore water pressure, is developed, and corresponding stability indices are formulated. Numerical methods are utilized to determine the optimal solutions of these indices. A comprehensive parametric study evaluates the influence of 3D geometric characteristics, HB parameters, and burial depth on tunnel stability. Results demonstrate the evolution of tunnel-roof stability as the critical depth-to-span ratio C/R increases from shallow- to deep-buried conditions; for the parameter combinations examined in this study, the critical C/R separating the two mechanisms ranges approximately from 0.15 to 2.0, depending on the rock-mass properties, pore-pressure condition, and tunnel geometry. Furthermore, stability charts correlating supporting pressure and factor of safety (FoS) in saturated strata are proposed to offer practical design guidance. Findings indicate that neglecting pore water pressure may significantly underestimate the structural stability, thereby emphasizing the necessity of incorporating hydrogeological effects in tunnel design. The proposed stability assessment framework provides theoretical support for the safe development of deep underground spaces under complex geological conditions, including deep energy exploitation, underground storage facilities, and related geotechnical engineering applications. Full article

The synchronous grouting layer in subsea shield tunnels is continuously exposed to seawater during long-term service. Sustained migration and diffusion of seawater ions can induce deterioration of the pore structure and degradation of mechanical properties, thereby diminishing the support and load-transfer functions provided to the segmental lining and ultimately compromising the long-term structural safety of the tunnel. In this study, synchronous grouting mortar obtained from an actual subsea shield tunnel project was subjected to freshwater and natural seawater immersion. Compressive strength tests and X-ray computed tomography were combined to investigate the evolution of mechanical properties and three-dimensional pore structure under prolonged exposure to natural seawater. Repeated scans were performed on the same group of samples at different immersion ages to determine total porosity, connected porosity, and pore connectivity. Quantitative relationships were then established between immersion time and both connected porosity and compressive strength. The results indicate that natural seawater exerts a pronounced influence on compressive strength at different stages, shifting from an initial enhancement to progressive deterioration during prolonged immersion. At 420 d, the compressive strength was approximately 23% lower than the peak value measured at 28 d. During prolonged immersion, total porosity increased gradually, whereas connected porosity and pore connectivity exhibited substantial increases. The difference shows that the internal structural evolution was governed primarily by the propagation and interconnection of existing pores and microcracks rather than by a substantial increase in total pore volume. With increasing immersion time, the pore structure progressively evolved from a dispersed and weakly connected state into a more continuous network of pores and cracks, accompanied by the enlargement and interconnection of local defects. The evolution of connected porosity with immersion time was well described by a square root function based on the characteristic time scale of Fickian diffusion, while the variation in compressive strength followed an exponential relationship. Increased connectivity of pores and cracks provided more continuous pathways for the inward transport of seawater ions and progressively disrupted the internal load-bearing framework, thereby contributing to the degradation of macroscopic mechanical properties. The findings provide experimental support for the durability design of synchronous grouting materials and the long-term maintenance of subsea shield tunnels. Full article

Previous studies of train-induced tunnel responses have mainly focused on completed tunnels or symmetric loading conditions, while the dynamic behavior of unfinished double-arch tunnels subjected to unilateral train loading through temporary trestles remains insufficiently understood. To address this gap, this study investigates the asymmetric load-transfer mechanism and short-term structural response of an unfinished double-arch tunnel–trestle system and identifies critical locations for construction-stage monitoring and speed control. A three-dimensional ABAQUS model was established for train speeds of 10–70 km/h and validated using a 63-day field-monitoring program comprising 15 train passages at speeds of approximately 9.4–56.2 km/h. Both numerical and monitoring results show that stress and deformation increase with train speed and are concentrated at the loaded-side invert, lower middle partition wall, and trestle wheel-load region. At 70 km/h, the calculated maximum lining compressive stress and trestle stress reached 6.353 and approximately 172 MPa, respectively, while the maximum horizontal deformations of the loaded and unloaded tunnel bores were 1.110 and 0.565 mm. At the maximum monitored speed of 56.2 km/h, the measured peak compressive stress of the middle partition wall was 5.95 MPa. The mean monitoring-to-simulation ratios for the evaluated responses were approximately 0.94–0.97, demonstrating satisfactory agreement and a slightly conservative numerical prediction. The results clarify the asymmetric coupling response of the tunnel–trestle system and support the identification of sensitive monitoring locations. Based on the combined numerical and field evidence, approximately 30 km/h is recommended as a conservative, project-specific construction-stage operational-control value. This study provides a quantitative basis for monitoring and risk control in similar temporary rail-transport projects, although further verification under different geological, structural, and loading conditions is required. Full article

The prolonged operation of semi-enclosed subway tunnels results in waste heat accumulation, energy wastage, and potential safety hazards. Integrating capillary heat exchangers (CHEs) with tunnel linings to form an energy tunnel is an effective approach to addressing these challenges. However, the current design methodologies for energy tunnels are still non-systematic, and the studies on the design optimization of CHE are still inadequate. To address these gaps, the shield energy tunnel demonstration project in Qingdao was selected as the research object, and a three-dimensional fluid–thermal coupled numerical model was established using the COMSOL simulation platform. A total of 48 CHE design configurations were analyzed to evaluate the heat transfer performance and temperature uniformity of the energy segment. The results indicate that the capillary bundle geometry and the installation position of the CHE are the dominant factors. Specifically, the I-shaped CHE achieves the highest heat transfer capacity, while the W-shaped CHE provides the best temperature uniformity. Installing the CHE within the inner arc protective layer, as opposed to the outer arc protective layer, significantly enhances the heat flux per unit area and improves temperature field uniformity. In addition, the reverse-return connection offers only a marginal advantage over the direct-return configuration, and the capillary group spacing exerts a relatively minor influence on both the heat transfer rate and temperature uniformity of the energy segment. This study provides a reference for the design and engineering application of subway shield energy tunnels. Full article

This study presents a comprehensive experimental and theoretical investigation into dual-gate field-emission devices fabricated using a standard 0.35 µm CMOS-MEMS process. Two emitter configurations, the concave-tip and triangular-tip, are characterized, and their performance is rigorously analyzed using three-dimensional simulations based on Fowler–Nordheim emission theory. To account for discrepancies between initial designs and fabricated devices, the influence of critical geometric parameters, including tip apex radius, cathode-anode spacing, and tip sharpness, is systematically evaluated regarding emission current and threshold voltage. Compared to the floating-gate baseline (~38 V), dual-gate (DG) operation lowers the threshold voltage by ~70% (~10 V), enhances low-voltage emission over tenfold, and provides a 3.4-fold boost in differential output conductance. Simulation analysis indicates this improvement stems from enhanced electrostatic field distribution governed by the gates. Furthermore, the top gate, due to its proximity to the emitter tip relative to the bottom gate, provides superior control over emission current at lower operating voltages. Three-dimensional simulations corroborate these findings, revealing that minimizing both the tip radius and cathode-anode spacing substantially enhances tunneling electron flow. Additionally, gate voltage sweeps confirm that electron trajectories are effectively directed by electrostatic steering. These findings establish critical design guidelines for integrating field-emission devices into standard CMOS platforms, facilitating the development of on-chip electrostatically controlled electron sources for integrated vacuum microelectronics. Full article

The tunnel portal section is one of the most seismically vulnerable parts of a tunnel, where strong earthquakes may trigger slope instability and induce plastic damage in the tunnel lining. Based on viscous-spring artificial boundary theory, a seismic oblique-incidence method applicable to tunnel portal sections is developed by incorporating the effects of slope topography. A three-dimensional finite element model is then established to investigate the seismic response and damage mechanisms of the tunnel portal section subjected to obliquely incident SV waves. The numerical calculation results in this study indicate that fully connected plastic deformation zones eventually develop in both the original slope site and the slope site with a tunnel structure, leading to slope instability characterized by downward sliding of the rock mass along a slip surface. However, in the presence of a tunnel structure, plastic deformation initiates simultaneously at the slope toe and near the tunnel portal. The maximum plastic strain is concentrated near the tunnel portal. Both topographic amplification and the accumulation of sliding debris markedly aggravate lining damage. The seismic-wave incidence angle, ground conditions and seismic-wave spectral characteristics all have pronounced effects on plastic deformation in both the slope site and tunnel lining at the tunnel portal section. In addition, tensile damage is more pronounced and extends over a wider area than compressive damage. At shear-wave velocities of 450–550 m/s in the upper soft-rock site, the damage zone is approximately two to three times the horizontal projection length of the slope, which is identified as the primary damage zone and should be regarded as a key seismic fortification area in tunnel design. Full article

The loss of sand foundation often induces differential settlement in immersed tunnel segments, potentially causing structural damage and reducing structural resilience. Accurately assessing the damage characteristics and their effects on resilience during sand foundation loss is essential for ensuring tunnel safety. This study adopts a typical immersed tunnel project as a case study. Long-term structural deformation data acquired by distributed optical fiber sensing technology and sand foundation detection data are adopted to analyze the response characteristics and damage state of the tunnel. A refined three-dimensional tunnel–stratum interaction model is established and validated against monitoring data to investigate mechanical response characteristics, including deformation and bending moment distributions. A redundancy factor is proposed as a quantitative index for tunnel resilience under foundation loss, and a multi-level resilience grading framework is established accordingly. Furthermore, the evolution of tunnel resilience under various displacement recovery ratios, which represent the extent of differential settlement remediation, is investigated using the refined numerical model. Field detection results show that over 50% of the foundation area is affected by loosening or voids. These defects are highly consistent with regions of abnormal structural deformation, leading to a bending–torsional deformation mode, with a maximum joint differential settlement of 106.7 mm. Stress concentration occurs in the tunnel floor above denser sand zones, with a maximum crack width of 0.43 mm. The tunnel is classified as severely damaged (low resilience) based on the proposed standard, with a redundancy factor of 1.59. Bending-torsional deformation and stress concentration are gradually mitigated as the displacement recovery ratio increases. The redundancy factor exhibits a parabolic relationship with the recovery ratio, indicating that tunnel resilience can be restored to a relatively high level when the displacement recovery ratio exceeds 70%. The proposed redundancy factor and grading framework provide quantitative guidance for designing and optimizing resilience improvement strategies following sand foundation loss. Full article

Fault fracture zones can act as preferential groundwater flow paths and significantly modify the seepage field around tunnels. To investigate the influence of the fault–tunnel intersection angle on pore water pressure distribution in tunnel surrounding rock, a three-dimensional steady-state Darcy seepage model was established using the F4 fault section of the Yinggeling Tunnel as a representative engineering background. Four cases were considered: a fault-free tunnel and tunnels intersecting fault fracture zones at fault–tunnel intersection angles of 45°, 90°, and 135°. Pore water pressures were extracted at the tunnel crown, invert, and left and right sidewalls at radial distances of 0.2 m and 10 m from the excavation boundary to characterize the near-field and intermediate-to-far-field responses. The results show that the fault fracture zone acts as a preferential drainage pathway and reduces the pore water pressure around the tunnel. Under the baseline permeability condition, the 90° intersection case produces the strongest pressure-relief effect, with peak pore pressure reduction ratios of 23.66–24.24%, followed by the 45° case with reductions of 20.54–22.22%, whereas the 135° case shows a weaker reduction of 4.74–5.36%. Sensitivity analysis indicates that the 90° case generally maintains the strongest pressure-relief effect under most fault-to-rock permeability ratios, although the differences among some intersection-angle cases decrease at high permeability ratios. The near-field surrounding rock exhibits rapid pressure dissipation controlled by tunnel drainage and fault-guided flow, whereas the intermediate-to-far field shows a smoother and more attenuated response. These findings clarify the seepage-control mechanism of the fault–tunnel intersection angle and provide a reference for waterproofing and drainage design in tunnels crossing fault fracture zones. Full article

The latest generation of 4D imaging radar demonstrates significant potential in autonomous driving environmental perception, leveraging its capability to provide target elevation data and dense point clouds. This paper introduces a complete method for constructing a multimodal 4D imaging radar dataset for three-dimensional traffic scenes. It illustrates the hardware and software configurations of the data-acquisition vehicle. Methods including multi-sensor coordination, parameter calibration, timestamp synchronization and spatial datum synchronization are proposed. And eight typical three-dimensional traffic scenarios are designed, such as rainy weather environments, dense heterogeneous targets, enclosed tunnels, high-speed cut-in of multiple vehicles, multi-layered stereoscopic structures and edge working condition reproduction. In addition, this paper puts forward a frame-by-frame processing method for high-resolution images and point cloud data collected by the high-definition camera-LiDAR-4D imaging radar collaborative system. A large model-based 3D annotation method for multiple types of targets is proposed, generating a spatio-temporal sequence-optimized four-dimensional annotation sequence, and finally constructs a complete and high-quality multimodal 4D imaging radar dataset for three-dimensional traffic scenes. The results show that the constructed dataset enables the synchronization of timestamps and spatial coordinate systems. The large model can achieve high-precision 3D annotation for the four predefined target types. The dataset contains 11,400 frames of data from high-definition cameras, LiDAR, and 4D imaging radar, with 131,642 labels. This study will provide reliable fundamental support for the training and verification of 4D imaging radar perception algorithms, vehicle decision-making and planning in complex scenarios, and multi-sensor fusion technologies. Full article

A computational fluid dynamics and conjugate heat transfer (CFD+CHT) methodology is developed for the thermal simulation of a commercial prismatic ${\mathrm{LiFePO}}_4$ cell under charging and discharging operating conditions. The approach couples a three-dimensional representation of the battery, including a simplified description of its internal layered structure, with an electrochemical–thermal heat-generation model implemented as a temperature- and time-dependent volumetric source term. The heat source is applied within the active layers of the cell and updated during the transient simulation according to the local thermal state and to the evolution of the state of charge. The methodology is applied to 1C and 2C cycles under natural convection and forced-air cooling at free-stream velocities of $10\mathrm{m}{\mathrm{s}}^{-1}$ and $20\mathrm{m}{\mathrm{s}}^{-1}$. A dedicated wind-tunnel campaign is carried out on the same cell, instrumented with type-K thermocouples distributed over its external surfaces, to provide experimental data for model validation. The results show that the proposed framework accurately reproduces the main wall-temperature trends observed experimentally. Under natural convection, the temperature distribution remains nearly uniform, whereas forced convection produces more pronounced vertical and in-plane gradients. For the charge cycles, the comparison between CFD predictions and end-of-cycle measurements yields a mean absolute error (MAE) of ${0.66}^{\circ }\mathrm{C}$ and a root-mean-square error (RMSE) of ${0.82}^{\circ }\mathrm{C}$ over 168 measurement locations. The discharge cycles yield a comparable level of agreement (MAE ${0.65}^{\circ }\mathrm{C}$, RMSE ${0.81}^{\circ }\mathrm{C}$ over 168 probe points), confirming the predictive capability of the methodology for both operating modes. Full article

In the construction process of a super-long-span short-distance continuous variable cross-section tunnel, multiple geometric mutations along the alignment induce significant discontinuity and asymmetry in the mechanical response of the surrounding rock-support system, which differs significantly from that of conventional single-variable-section tunnels. This aggravates local asymmetric stress concentration and sudden deformation surges, posing severe construction risks. To reveal the influence of different excavation methods on the mechanical response of the surrounding rock-support system during the construction of this type of tunnel, the Tangshan Road Interchange and Connection Line Project was added based on the Qingdao Qingyin Expressway. The large-span continuous variable cross-section sections of A, B, and C in the north line of the Tangshan Road Tunnel were selected as the research objects, and a three-dimensional finite element numerical model was established and rigorously validated against field monitoring data from three representative cross-sections. Three typical construction methods—the Distributed Bench Excavation Method (DBM), Double Sidewall Drift Method (DSM), and Distributed Double Sidewall Drift Method (DDSM)—were systematically compared and studied. The results indicate that the section transition zones (A → B and B → C) are the most sensitive key control areas. Compared with DBM, DDSM significantly reduced the vault initial support stress in Section A by 38.1% (from 6.51 to 4.03 MPa), the left and right spandrel stresses by 17.9% and 26.9%, respectively, and peak bolt axial forces by over 20%. Although DSM achieves maximum lateral convergence reduction (reducing haunch convergence by 32.8% in Section C), DDSM delivers the optimal comprehensive control by effectively restricting vault settlement and balancing support stress distribution. The field monitoring trend was highly consistent with the numerical simulation results, which confirms the accuracy of the established model. The research results can provide a reference for the selection of construction methods and deformation control of large-span continuous variable cross-section tunnels. Full article