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.

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.

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.

The seismic response of underground structures within integrated underground-aboveground structure system (IUASS) is influenced by both kinematic effect from the surrounding soil and inertia effect from aboveground structures, leading to complex dynamic responses. This paper investigates the seismic response of underground structures in IUASS. Dynamic simulations are conducted using both elastic and elastoplastic constitutive models. The results show that the mean period of input motion and the fundamental period of the free field significantly influence the drift ratio of the underground structure, while the force at the base of the aboveground structure is also strongly correlated with the drift ratio of the underground structure. The vertical displacement of the underground structure is strongly affected by the weight of the IUASS and excess pore pressure generated in the soil. Simplified analysis methods for predicting drift ratio and vertical displacement are subsequently proposed taking these factors into consideration. The proposed methods exhibit excellent agreement with dynamic analysis results across a wide range of input motion and structure conditions, providing important tools for seismic design of IUASS.

The freezing and grouting methods are among the main construction techniques for the lateral connection passages of shield tunnels in soft soil areas. Therefore, the surrounding rock undergoes freeze-thaw (FT) and dry-wet (DW) cycles caused by water level changes during operation, leading to the deterioration of mechanical properties and instability. However, this research achievement is very limited. In this study, the macro and micro damage mechanisms of the surrounding rock in lateral connection tunnels under FT and DW cycles were systematically investigated. Initially, clay was sampled from a cross-tunnel of Hangzhou Metro Line 4 in Zhejiang Province. Cement (NXI), ground granulated blast furnace slag (GGBS), and fly ash (FA) (NXII) were used to solidify the clay subjected to DW and FT cycles. Finally, the uniaxial compressive strength and microstructure were examined using scanning electron microscopy and X-ray diffraction (XRD) to obtain 15 DW cycles (0, 5, 10, 15) and 12 FT cycles (0, 4, 8, 12) after 7 and 28 d curing periods. The results indicated that the compressive strength decreased after the DW-FT cycles, with rod-like hydration products (macropores) transitioning to needle-like ettringite (AFt) in the micropore-dominated structures. Simultaneously, the GGBS-FA mixture (NXII) promoted tight microstructures via hydration-induced bridging and pore filling, enhancing the water stability by 23% and DW-FT resistance by 18% compared with cement-only formulations. The NXII composite demonstrated superior long-term strength retention (89% at 180 d) and formed distinctive hydration phases, including calcium silicate hydrate and hydrotalcite-like compounds. Subsequently, the increasing pressure on the surrounding rock was calculated to degrade its mechanical properties (20% and 24.4%, respectively). Finally, a life-cycle assessment confirmed that the GGBS-FA system reduced material costs by 35% and carbon emissions by 42% compared with conventional cement-lime stabilization. These findings elucidated the microscale hydration damage mechanisms of GGBS-FA systems for soft soil solidification to advance sustainable tunnel engineering.

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.

With the development of large-scale mechanized construction techniques, tunnel excavation is predominantly executed using either full-face or large-face methods, often supplemented with anchor-bolt reinforcement. However, the reinforcement mechanism of prestressed anchor bolts and the impact of excavation methods on the anchorage layer are yet to be comprehensively clarified through an integrated lens that bridges the macroscopic bearing capacity with mesoscopic mechanical properties. In this study, diverse support types and excavation methods were considered to perform a comprehensive series of loading and failure tests on tunnel anchorage layers. Through the incorporation of stress monitoring, P-wave velocity analysis, and particle image velocimetry (PIV), this study revealed the reinforcement mechanisms of prestressed anchor bolts. In parallel, it delineates the influence of excavation methods on both the macroscopic bearing capacity and mesoscopic mechanical properties of the anchorage layer. The experimental findings revealed that prestressed anchor-bolt reinforcement induced a progressive evolution in the surrounding rock, characterized by sequential modifications in stress, integrity, mechanical properties, ductility, and bearing capacity. Relative to the unsupported conditions, the prestressed anchor-bolt reinforcement yielded substantial enhancements: stress improved by approximately 245.5%, integrity by 14.3%, mechanical properties by 9.8%, ductility by 147.7%, and bearing capacity by up to 500%. In unsupported conditions or with anchor bolts, large-face excavation demonstrated superior performance relative to full-face excavation, enhancing both the mesoscopic mechanical properties and macroscopic bearing capacity by approximately 2.8%-6.9% and 50%-100%, respectively. The findings indicate that large-face excavation is the preferred method under these support conditions. However, when prestressed anchor-bolt reinforcement is used, the differences between the two construction methods become negligible, rendering full-face excavation the more practical construction option.

The emission of hazardous gases from surrounding rocks is one of the major factors threatening the safety of deep underground engineering construction. In particular, for non-coal-bearing strata, increasing attention has been paid to identifying the types of hazardous gas reservoirs and predicting the gas release patterns from the surrounding rock. This study reveals the generation and occurrence mechanisms of hazardous gases within magmatic rock strata in the Qinghai-Tibet Plateau. Based on the characteristics of the gas reservoirs, a model test was conducted to analyze the deformation of the surrounding rock and the gas migration behavior during tunnel excavation. To represent the characteristics of low-porosity magmatic rock fracture reservoirs, a gas migration-release evolution model was developed based on the ideal gas law. The evolution of gas migration and release in the surrounding rock throughout the tunnel excavation process was investigated. Furthermore, the influence of borehole layout on the tunnel face on the gas release efficiency was examined. The results show that the long-term gas release process can be divided into three stages: stable release stage, gas replenishment stage, and residual gas release stage. Before the tunnel intersects the reservoir, the gas escape is primarily driven by pore seepage. After the tunnel enters the reservoir, the fracture gas velocity increases rapidly and then decreases gradually, with the escaping gas predominantly originating from the reservoir fractures. In addition, the installation of exhaust boreholes results in an "S-shaped" increase in the gas flow volume at the tunnel face as the borehole area increases. The gas release efficiency is maximized when the ratio of the fracture trace length to the exhaust borehole area (l/a) ranges between 0.064 and 0.096. These findings provide deeper insights into the gas migration and release characteristics of tunnel surrounding rocks in magmatic rock strata.

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.