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.

The development of large cross-section tunnels is an inevitable trend driven by the intensification of coal mining activities and advancements in mining equipment technology. However, the disturbance stress exerted by adjacent caverns has a more pronounced impact on weakly cemented rock strata in the vicinity of neighboring tunnels. To mitigate deformation in weakly cemented tunnels, grouting and the installation of long anchor cables were employed to reinforce the self-supporting capacity of the surrounding rock, thereby establishing an active support layer. Additionally, U-shaped steel frames combined with the subsequent application of flexible filling materials were utilized to aid the surrounding rock in mobilizing its self-supporting capacity, which resulted in the formation of a passive support layer. A layered collaborative control methodology integrating both active and passive support mechanisms was developed and implemented in engineering practice. The findings demonstrate that the vertical stress was alleviated after cavern excavation and was predominantly transferred toward the adjacent tunnel, with the influence zone extending approximately 7 to 12 times the tunnel height. Conversely, the horizontal stress is primarily dispersed laterally, affecting a region approximately 3 to 6 times the tunnel width. Following the infilling of pebbles between the U-shaped steel frame and the adjacent rock mass, the maximum compressive stress experienced by the U-shaped steel frame decreased by 50%. Additionally, the spatial extent of the maximum axial force was reduced by 65%, whereas the stresses within the rock bolts and cable bolts increased by 30% and 40%, respectively. Grouting reinforcement contributed to bonding and compaction effects on the delamination and fracturing of the roof strata, with the grout predominantly distributed within a range of 1.5 to 5 m from the central region of the roof. The research outcomes presented in this paper can provide valuable reference for a large-section weakly cemented tunnel.

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.

This study investigates the macro- and micro-mechanism of synchronous tail grouting in ground surface settlement (GSS) control of coarse-grained strata through a computational fluid dynamics-discrete element method (CFD-DEM) coupled model, focusing on two grouting port configurations (Type I: upper-lower symmetrical layout; Type II: lateral staggered distribution) in six-grouting-port shield machines. Analyzing particle contact characteristics and force chain evolution patterns, the connection between particle-scale behavior and macroscale GSS during grouting is elucidated. Key findings demonstrate that grouting duration is the primary factor for GSS development. Grout injection disrupted the particle contacts and force-chain networks above the tunnel center, weakening natural arching and redistributing interparticle forces. The central axis of the soil-arching effect exhibited a strong linear correlation with the spatial position of the uppermost grouting port. The soil located 0.25D-0.5D (where D represents the tunnel diameter) from the tunnel centerline horizontally, exhibited heightened sensitivity to grouting, with a low fabric anisotropy (α) and oscillating principal direction (β) sharply between 0° and 180°, reflecting pronounced displacement and isotropy. This study provides theoretical support for intelligent shield machine selection and grouting strategy optimization in geotechnical engineering, with significant implications for soil displacement control in complex strata.

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.

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.

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.

An earthquake with a magnitude of 6.6 (M_W) occurred in Menyuan County, Qinghai Province, China, on January 8th, 2022. The Daliang Tunnel, which traverses the seismogenic fault, was severely damaged during this seismic event. The seismic damage investigation of the tunnel is introduced, and the damage characteristics along the tunnel are also presented. It is found that the damage severity of the tunnel is highly correlated with the distance to the fault. Damage modes for different tunnel zones (cross-fault zone, portal zone, and ordinary zone far from the fault and the portal) are quite distinct. Based on the understanding of seismic damage to the Daliang Tunnel in 2022 Menyuan Earthquake, as well as other damaged tunnels during the 2008 Wenchuan Earthquake, the critical influence factors for damage to cross-fault tunnels are discussed. From the seismic investigation, coupling effects of strong ground motions and fault dislocations are highlighted, which pose significant risks to cross-fault tunnels and should be considered in the seismic design for such tunnels. The deformation joints of the tunnel could help the tunnel adapt to the deformation caused by fault dislocation, and thus protect the main structure, but inversely an added local deformation may be expected around the deformation joints. The instability of the overlying slope may have contributed to the local amplification of the fault dislocation along the Daliang Tunnel. Finally, the requirements of seismic resilience for cross-fault tunnels are proposed, and detailed suggestions are provided to enhance the seismic performance of such cross-fault tunnels.

Actual seismic events typically exhibit mainshock-aftershock sequence characteristics, and source characteristics have a significant impact on cavern response. Currently, the influence of near-fault mainshock-aftershock sequences (NFMA) and far-field mainshock-aftershock sequences (FFMA) on underground caverns is generally ignored. This study aims to establish a framework for evaluating the dynamic response characteristics and seismic fragility of large-scale underground caverns under NFMA/FFMA. The response laws of residual displacement and rock fracture degree of cavern under NFMA/FFMA are comparatively studied, and the failure probability of different damage states is quantified by the fragility function. The results show that the surrounding rock of underground caverns exhibits significant cumulative damage effects and non-uniform failure characteristics under mainshock-aftershock sequences. Aftershock fragility is strongly related to the mainshock-damaged state for underground caverns. The collapse probability of underground caverns after 0.9g aftershocks in NFMA increased from 0.76% in slight damage to 21.12% in moderate damage and 53.51% in severe damage. This study can provide a probabilistic basis for seismic design, aftershock risk warning, and post-earthquake emergency assessment in underground engineering.

The effective prediction and evaluation of the long-term stability of deep-buried tunnels are crucial for tunnel design, construction, and operation. The creep model is key to predicting time-dependent behavior, and the accuracy of time-dependent deformation predictions is determined by the creep parameters. This paper introduces a novel fractal-order elasto-visco-plastic creep damage (FEVPD) model that incorporates long-term strength into the damage evolution equation within the framework of continuum damage mechanics. The model effectively captures the three-stage creep behavior of various rock types and predicts their creep lifespans under different stress levels. The FEVPD model was implemented in FLAC3D using C++. Additionally, in determining the creep parameters of rock at the engineering scale to address the high computational cost of parameter inversion, an improved genetic algorithm was developed with adaptive perturbation, elitism, and dynamic mutation mechanisms. Application to field monitoring data from the Jinping II hydropower station tunnel demonstrated that the FEVPD model improved the prediction accuracy of time-dependent deformation by 32.68% compared to the classical Burgers-Mohr (CVISC) model. The enhanced inversion method also reduced the final error by 26.0% and 22.7% for the FEVPD and CVISC models, respectively, compared with the standard algorithm. Finally, this model was used to predict the long-term stability of the tunnel. The results provide a reliable and efficient framework for modeling and predicting creep behavior in deep rock engineering.