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.

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.

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 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.

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.

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.

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.

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.

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.

Super-large-diameter shield tunneling inevitably induces deformations in the surrounding soil and nearby existing tunnels due to ground-tunnel interactions. This study developed and validated a numerical model to simulate these interactions in typical soft soil strata in Shanghai, with a focus on stress and displacement responses during the undercrossing of an existing tunnel by a new super-large-diameter shield tunnel. The study identified an incomplete soil arching (ISA) effect and proposed methods to delineate the ISA, loosened, and compaction zones, categorizing the influenced areas into reinforced, stable, and safe zones. Parametric analyses examined the influence of tunnel spacing (S) and volume loss ratio (V) on ground deformation, loosened zone height, and existing tunnel deformation. Results indicate that greater volume loss ratios and smaller tunnel spacings amplify ground settlement, while the loosened zone height is affected by both the volume loss ratio and the stratigraphic boundary. Among the considered scenarios, a volume loss ratio of 0.2% minimizes the loosened zone height across various spacings. Changes in the convergence of the existing tunnel occur in two phases, characterized by rapid changes (S/D of 0.1-0.3, where D is the diameter of the newly constructed tunnel) and gradual changes (S/D of 0.3-0.7). To mitigate adverse effects on the ground and the existing tunnel, it is recommended to maintain the volume loss ratio below 0.2% and the tunnel spacing over 0.3D. Additionally, reinforcing the loosened zone is advised to enhance the stability of the existing tunnel.