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.

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.

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.

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.

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.

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.

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.

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.

Reliable data sources are essential for intelligent tunnel construction, yet on-site data are often insufficient to meet sample require-ments. Previous numerical modeling studies have seldom considered the combined effects of different excavation methods' spatial effects and the distribution characteristics of joints. This paper develops a method to construct a stability database for jointed rock tunnels with primary support systems using a computational framework combining the finite difference method-discrete element method (FDM-DEM). The framework constructs a 2D model using the Mohr-Coulomb criterion and a 3D model with the Hoek-Brown failure criterion, enabling the stress release process to accurately replicate the influence of joint distribution features and excavation space effects in the 2D calculations by utilizing the longitudinal deformation profile parameters of the bench sections and fine-grained ground reaction curves. The computational circle is determined by grid research and data analysis, while the performance differences of various primary support components and their correlations with surrounding jointed rock are analyzed using the control variable method. The validity of the framework is initially confirmed by case comparisons and macroscopically validated using the Mantel test and Spearman analysis on the constructed simulation database—containing tunnel construction information, joint distribution, rock mechanics parameters, and stability indices—thereby establishing a reliable foundation for machine learning and transfer learning 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.

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.

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.

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.