In tunnel approach zones (TAZs), drivers must complete a sequence of tasks, including detecting the tunnel, identifying speed limits, and decelerating to enter safely. However, current standards mandate only stopping sight distance (SSD) compliance of TAZs, which may not suffice for all of these complex driving tasks. In this study, we investigated (1) whether SSDs are sufficient for driving tasks in TAZs, (2) the impacts of restricted visibility conditions on cognitive-behavioral processes, and (3) the appropriate visibility condition of TAZs. We selected tunnels with three visibility conditions to conduct both subjective tests of perception and experiments with real vehicles. We propose a research framework called the task analysis of driving scenarios modified predictive processing model (TADS-MPPM). We then construct a multidimensional framework that includes sequences of behaviors and cognitive tasks (with 4 driving behavior nodes and 4 cognitive nodes) for spatiotemporal profiling, as well as active deceleration coefficients (safety and efficacy coefficients) and cognitive-behavioral workload (measured using the extended Jaccard coefficient). Then, we use an MPPM to visualize the evolution of driving predictions, driving behaviors, and sensory inputs during the approach to the tunnel. Finally, we explore the risk mechanisms of TAZs. The results show that SSD designs (1) delay tunnel detection, speed-limit recognition, and deceleration initiation, as well as compressing behavioral-cognitive chains, and (2) degrade safety and compliance due to overloaded operations and cognition. Conversely, ensuring that critical tunnel information is discernible at a longer decision sight distance provides the necessary margin of safety on the road. This creates adequate space and time to perform progressive deceleration to eliminate task compression and restore composed and smooth driving maneuvers.

This study investigated the long-term settlement behaviour of piled buildings induced by shield tunnelling in soft ground conditions within urban environments. By integrating a detailed case study with advanced numerical modelling techniques, this study provided a nuanced understanding of the interactions between tunnel construction and existing pile foundations. Central to the investigation is the role of soil consolidation, which significantly contributes to the settlement of piled buildings. To address this, this study emphasizes the critical need for the precise calibration of tunnelling parameters such as face pressure and grouting pressures. These parameters are meticulously controlled to mitigate the adverse effects on nearby piled buildings, ensuring their stability and integrity. It is established that an optimal face pressure, set at 90% of the lateral earth pressure, consistently minimizes the settlement of piled buildings, primarily due to the minimal reduction in the pile toe resistance observed near the tunnel. Similarly, the ideal grouting pressure was identified to be within the range of 120%-160% of the vertical earth pressure, with the smallest building settlement and decrease in pile toe resistance observed at a grouting pressure of 150% of the overburden pressure. This finding elucidates the load transfer mechanism within piled buildings. This study further demonstrated that the settlement induced by the second tunnel excavation is smaller than that caused by the first tunnel excavation owing to the sheltering effects of the adjacent first tunnel and pile foundations. During the consolidation phase following tunnel excavation, the settlement caused by the second tunnel is smaller than that caused by the first tunnel, which is attributed to the dissipation of the negative excess pore pressure around the first tunnel, leading to soil volume expansion. These insights not only validate the effectiveness of the numerical model but also contribute significantly to the field of geotechnical engineering by providing actionable guidelines for future tunnelling projects.

To mitigate the defects of shield tunnels in operation, a reinforcement method using corrugated plates was proposed. This paper aims to present a comprehensive investigation of the effectiveness of this method. Taking into account the corrugated plate joints, full-scale tests were designed and conducted on two specimens of segmental joints: one unreinforced and one reinforced. The test results revealed that the failure mode of the reinforced specimen was characterized by shear failure of the chemical anchors, followed by concrete crushing. The effectiveness of reinforcement highly depends on the shear capacity of the chemical anchors. After reinforcement, the flexural stiffness and ultimate bearing capacity of the specimen increased by 112.4% and 32.5%, respectively. Two refined numerical models, developed at both the joint scale and full-ring scale, were validated for corrugated plate reinforced shield tunnels. The numerical results indicated that, with full-ring reinforcement, the overall stiffness and the bearing capacity increased by 341.4% and 39.6%, respectively. Notably, shear stress in the chemical anchors was more pronounced at the tunnel vault and haunch, suggesting the need for localized optimization of the chemical anchors in these areas.

Accurate TBM performance estimation is essential for effective tunnel design and planning. This study introduces a one-dimensional (1D) estimation model that estimates thrust, torque, power, cutterhead speed, and tool count using only excavation diameter. The model was developed across four TBM types—open, single shield (SS), double shield (DS), and earth pressure balance (EPB)—to isolate the influence of diameter from other variables. Validation against existing models and a 52-case independent dataset confirmed strong correlations: torque scales with the cube of the excavation diameter (R² = 0.89 for EPB), power grows faster than linearly (R² = 0.83 for EPB), thrust increases supra-linearly (R² = 0.79 for EPB), and cutterhead speed decreases with diameter (R² = 0.87 for open TBM). Tool count grows proportionally. A reliability matrix compares model accuracy and data support, aiding selection based on both fitness and robustness. This 1D model offers fast, consistent estimates for early-stage assessments. While it excludes detailed geological input, it is suited for feasibility studies and preliminary design. Future work will incorporate additional ground and machine parameters and extend validation across a broader range of tunneling conditions to enhance generalizability.

Leakage disasters in shield tunnels frequently occur, leading to severe consequences such as tunnel collapse, road collapse, and building destruction. Since it is difficult to record the accident evolution process onsite, it is necessary to reproduce it through credible numerical simulations. However, traditional numerical methods face technical bottlenecks when simulating water-sand inrush in shield tunnels due to challenges such as large deformation analysis and fluid-structure coupling, making it difficult to simulate the process of disaster progression. To address this issue, a Coupled Eulerian-Lagrangian (CEL) method incorporating seepage analysis, referred to as the S-CEL method, was proposed to simulate the interaction between water, soil, and a shield tunnel during a disaster. A refined three-dimensional numerical model was developed using the S-CEL method to simulate the water-sand inrush process. The generation sequence of new leakage points at the segment joints and the mechanisms driving the progression of the disaster were revealed. New leakage points were progressively generated along the longitudinal direction of the tunnel. As the number of leakage rings increased, the amount of soil loss increased rapidly. This led to severe uneven settlement and dislocation deformation of the tunnel. A channel steel was introduced to reinforce the tunnel in the numerical simulation to mitigate or decelerate the progression of the leakage disaster. The connection method between the channel steel and tunnel segments was found to be pivotal to the strengthening effect. Employing only bolt anchoring showed limited efficacy, while enhancing the segment-steel interface with epoxy resin achieved much better performance in mitigating disaster progression.

Burial depth and spacing are key factors influencing the stability of compressed air energy storage chamber groups. However, methods for determining safe burial depth and spacing in aligned multi-chamber systems remain underexplored. This study introduces a modified linear superposition method (M-LSM) for calculating elastic stress tensor fields in the surrounding rock around multiple chambers. The method analyzes the distribution of elastic stress under varying design parameters and surrounding rock conditions, identifying the most critical stress locations, which are the sidewalls affected by adjacent chambers, and providing deeper insights into stress concentrations caused by chamber interactions. The relationship between safe burial depth and spacing follows an approximately inverse proportionality, with the safety criterion of no plastic zones developing in the surrounding rock. A closed-form solution for safe burial depth and spacing is derived, which can be used to quickly determine the design parameters. The M-LSM is applicable to a wide range of internal pressurized chamber groups and borehole problems, capturing mutual interactions between adjacent chambers more realistically. Compared to finite element method simulations based on a practical engineering case, the results show errors that are typically negligible, validating the reliability of the analytical approach. This fully analytical method is mesh-free, iteration-free, and offers infinite resolution, making it highly efficient for both computations and practical applications. The closed-form solution derived from this method provides significant value for trend analysis, practical calculations, and engineering applications.

As shallow underground resources are depleted, urban development is extending to greater depths, necessitating a clear understanding of soil arching at various burial depth conditions. Laboratory trapdoor tests equipped with embedded soil-pressure cells and digital image correlation captured the ground-reaction curve and soil deformation. The results reveal pronounced discrepancies between shallow and deep burial. In shallow conditions, soil arching undergoes a "failure-reconstruction" process: soil pressure plunges, then rebounds to stability. In deep strata, the arching forms rapidly and attains stability almost immediately after the minimum pressure is reached. Shallow tests generate several horizontal displacement bands rising to 4.8B (B, trapdoor width); deep tests yield one stable band, with its influence height reduced to about 3.0B. Vertical displacement above the trapdoor evolves through 'triangular-tower-para bolic" stages to 4.3B in shallow tests, but follows a persistent parabolic profile limited to 2.7B in deep tests. Additionally, shear bands under deep conditions form at smaller angles and are more vertically oriented. These findings expose the fundamental differences in deformation mechanisms between shallow and deep burial and provide quantitative criteria for depth zoning in urban underground space development.

Despite the thriving development of metro-led urban underground public space (UUPS) and its significant benefits and costs, there remains a critical research gap in understanding and evaluating its efficiency. This paper intends to improve the post-evaluation system of metro-led UUPS by proposing an efficiency evaluation framework based on data envelopment analysis. The public and the private sectors are taken as different coexisting decision-makers, and a pair of linear programming is built accordingly (with different assignments of discretionary and non-discretionary inputs) for each decision-making unit. The directional vector is calculated based on CRITIC weights to model the searching process of referential cases in terms of urban renewal. The empirical study of twenty metro-led UUPSs in central Shanghai reveals that (1) the proposed evaluation framework is feasible and discriminative, (2) the efficient form of metro-led UUPS in Shanghai is mainly limited to a compact pattern with a low proportion of pure public space, (3) the essential solution to promote efficiencies is closer cooperation between different parties, and (4) efficiency evaluation is crucial to avoiding the "the-more-the-better" type of development. The findings of this study are expected to shed light on the future planning and operation of metro-led UUPS.

Shallow-buried urban road tunnels with shafts (URTS) have reduced traffic congestion in large cities. During fire scenarios, the backflows occur at those shafts far away from the fire source inhibiting smoke exhaust, but its rules have been unknown. A 400 m (length) × 12 m (width) × 5.5 m (height) physical model with 6-7 shafts over the ceiling is established using fire dynamic simulator software. The simulations are carried out after validation by both a small-scale experiment and a full-scale experiment. A total of 16 cases with 4 heat release rates (HRRs) and 4 spacing of fire source from the nearest unit shaft #1-1 (s_f-us1), are designed. Results indicate that the smoke spreading length is nearly independent of HRR but increases with s_f-us1. Ceiling smoke temperatures follow the power exponential laws, and the attenuation coefficients decrease with the increase of HRR and s_f-us1. The farther away from the fire, the more likely the occurrence of shaft backflow. A good power exponential rule of the shaft negative mass flow rate is fitted out, and values of decay coefficient b₂ range from 0.56 to 1.0. Based on dimensional analysis, a power exponential rule of the shaft dimensionless net mass flow rate is fitted for the exhaust shafts and a linear rule for the backflow shafts. The shaft neutral plane heights range from 1.4 m to 3.6 m for the exhaust shafts and 3.2 m to 5.4 m for the backflow shafts. Also, a linear rule is fitted. This study establishes the smoke backflow theory in URTS during fire scenarios and contributes to the tunnel fire protection engineering.

Hyperspectral imaging provides a novel approach for intelligent geological perception in tunnelling and underground engineering due to its high spectral resolution, nondestructive nature, and combined spectral-spatial information. However, in confined underground spaces, noise is often introduced by short exposure times, low illumination, and dust, and limited spatial resolution can cause mixed pixel effects, complicating data processing. This study presents an underground hyperspectral imaging-based mineral mapping method that achieves wall-rock visualization and semi-quantitative mineral mapping through image denoising and spectral unmixing. A spatial-spectral recurrent transformer U-Net is developed to reduce noise by leveraging spectral band correlations and nonlocal spatial-texture dependencies. A Dirichlet-based mixed pixel simulation is used to address spectral mixing, with the N-FINDR algorithm identifying endmember minerals, and the fully constrained least squares method to estimate mineral abundances. When applied to a water diversion tunnel in Shanxi, the method generates spatial distribution maps of dolomite and calcite. The experimental results confirm its effectiveness for intelligent geological logging and subsurface geological feature analysis.