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.

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.

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.

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.

Blasting excavation is widely used in engineering, often involving complex whole layouts. However, the small size of the blasthole and the large size of the three-dimensional (3D) numerical model lead to the large calculation scale of the 3D blasting numerical simulation, which requires considerable calculation time. Typically, a 3D numerical model is simplified into a two-dimensional (2D) numerical model, and a 1/2- or 1/4-scale model can be adopted to reduce the calculation scale. To solve this problem, a one-dimensional bar explosion model is adopted to replace the traditional solid explosion model under the framework of the continuous-discontinuous element method. The detonation pressure is directly distributed to the elements penetrated by the bar, and the volume expansion of the elements is used to calculate the volume expansion attenuation detonation pressure at each stage of detonation, thus avoiding the problem of local mesh refinement. Compared with the solid explosion case, the reliability of the bar explosion model is verified by the propagation of the explosion stress wave, peak explosion pressure, and damage nephogram. In combination with the engineering background, three blasting conditions are simulated, and the optimal one is evaluated based on fracture degree and blast fragment size pass rate.

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.

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.

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.

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.

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.