Search Results (758)

Tunnelling-induced safety risks from adjacent piles have become increasingly severe with the rapid development of urban underground space. Model tests have become essential for revealing the complex pile-tunnel interaction mechanism. This paper reviews the research progress of model tests on the influence of single-line tunnelling on adjacent piles, focusing on test soil materials, tunnel simulation methodologies, analysis of test results, and research prospects. However, current model test studies are constrained by several critical limitations, including insufficient similarity between soil materials and prototype conditions, and overly idealized simulation of tunnel excavation. This paper identifies a significant research gap: the inability of current volume-loss techniques to capture 3D dynamic factors (e.g., face pressure and grouting timing) and the lack of meso-scale observation at the pile-soil interface. This review provides a systematic synthesis of these methodological challenges and proposes future research prospects to provide a more scientific basis for engineering design and risk control. Full article

The efficient treatment and resource utilization of shield tunnel spoil (STS) are important for sustainable underground construction in China. To improve the early mechanical performance and microstructural compactness of stabilized STS, this study investigated the solidification effect of a novel early-strength cementitious agent (ESCA) and compared it with ordinary Portland cement (P.O 42.5). Macroscopic mechanical tests, including unconfined compressive strength (UCS), stress–strain behavior, mass, and P-wave velocity measurements, were combined with scanning electron microscopy (SEM) and computed tomography (CT) analyses to reveal the mechanical response and microstructural mechanisms of stabilized STS. The results indicate that, compared with P.O 42.5, ESCA exhibits superior fluidity at lower water-to-solid (w/s) ratios, significantly shorter setting times, and higher compressive strength at all curing ages. The solidification efficiency of ESCA for STS is notably superior to that of P.O 42.5, with the peak strength, elastic modulus, mass, and P-wave velocity of ESCA-solidified specimens being higher than those of P.O 42.5-solidified specimens across the five dosages. Furthermore, ESCA material bonds more tightly with STS particles, resulting in lower porosity and a denser microstructure under the same stabilizer dosage. Overall, the combination of macroscopic mechanical properties and microstructural characterization demonstrates that ESCA material exhibits significant advantages in the efficient solidification and resource utilization of shield tunnel spoil. Full article

With the growing scarcity of surface space, underground development has become essential for expanding human living space. Among various tunneling methods, pipe jacking stands out due to its economic advantages and minimal environmental impact. Recently, vertical pipe jacking has been explored as an innovative technique for constructing shafts that connect horizontal tunnels to the ground surface. However, the evolution of jacking force during vertical pipe jacking with increasing jacking distance remains poorly understood. Understanding this evolution is critical for selecting jacking equipment, designing the horizontal tunnel lining against reaction forces, and preventing construction failures. Unlike horizontal pipe jacking where self-weight is negligible, the proposed model reveals that in vertical pipe jacking the self-weight of the pipe and machine above the excavation face increases with jacking distance while the overburden pressure decreases, resulting in a parabolic-like jacking force trend—a novel finding not reported in previous pipe jacking literature. This paper proposes theoretical formulas to quantify the three components constituting the jacking force: face resistance at the cutting head, frictional resistance along the pipe surface, and the dead weight of the machine and pipe above. The influence of jacking distance on each component is systematically analyzed. Parametric studies under standard and varied conditions reveal that under standard conditions, jacking force follows a parabolic trend—rapid initial increase, followed by slower growth, and eventually a slight decrease. The maximum jacking force consistently occurs at L = L₀ − 1 m, identifying the most unfavorable construction stage where special attention to tunnel lining deformation is required. Increasing outer diameter transitions the force curve from quasi-parabolic to “half diamond” shape, while doubling the friction coefficient approximately doubles the jacking force. These findings provide practical guidelines for vertical pipe jacking design and construction, including equipment capacity selection, friction reduction strategies, and monitoring priorities. Full article

To investigate the failure characteristics of 3D-printed concrete utility tunnels under loading, a 1:25 scaled model was designed using similarity theory. Vertical loading tests were conducted under soil lateral confinement, and the load–displacement curves, discrete-point strain responses, and crack evolution process were obtained. The test results show that the structure successfully undergoes an elastic stage, a crack development stage, and a plastic failure stage. The incorporated polypropylene fibers exert a bridging effect, enabling the component to retain a certain load-bearing capacity after cracking. Crack distribution was highly heterogeneous: cracks were densest on the top slab, widest on the side walls, and multi-directional on the inner wall. A clear correspondence exists between strain response and crack distribution, with tensile strain zones highly coinciding with crack opening zones. The failure mode generally agrees with the “top slab compression–side wall tensile cracking” characteristic of traditional closed-frame structures. However, the wall thickness deviations induced by the 3D printing process are amplified during internal force redistribution in the statically indeterminate structure, resulting in markedly asymmetric failure of the left and right side walls. Full article

This study develops a quantitative risk assessment framework that explicitly incorporates site-dependent variability in NATM (New Austrian Tunneling Method) tunnel construction projects. The underlying motivation is that identical risk factors can exhibit substantially different risk levels depending on project-specific site conditions. Conventional risk assessment approaches, which rely primarily on probability and impact ratings, are inherently limited in their ability to capture such variations across different project environments. To address this gap, key site condition factors affecting NATM tunnel construction were systematically identified and integrated into the existing risk assessment framework through a structured scoring and weighting process. Eight site condition factors were selected based on an extensive review of domestic and international literature, underground safety evaluation reports, tunnel design standards, geotechnical information databases, standard cost data, and expert consultation. These factors—Geotechnical Condition, Construction Schedule Float, Construction Budget Contingency, Spoil Bank Location, Likelihood of Civil Petitions, Underground Water Level, Environmental (Noise, Vibration), and Site Accessibility (Traffic Constraints)—were each quantified using a five-level scale ranging from 0.6 (very favorable) to 1.4 (very unfavorable). Subsequently, a composite site condition index was derived by combining the assigned scores with corresponding weights, and this index was incorporated as an adjustment coefficient into the conventional risk scoring system. The results demonstrate that, when the composite site condition index is considered, both the final risk magnitude and management priority vary depending on site-specific conditions, even for identical risk factors. This indicates that the proposed framework provides a more refined representation of actual project environments than traditional probability–impact-based approaches. The model can also serve as an effective decision-support tool for developing risk mitigation strategies tailored to specific site characteristics. Accordingly, the proposed model enhances the accuracy of risk assessment in tunnel projects and facilitates the rational identification of critical risks requiring prioritized management. However, because certain evaluation criteria rely on expert judgment, further validation through diverse real-world case studies and improvements to the objectivity of the evaluation framework remain necessary. Full article

Thermal pollution in underground spaces is one of the current challenges faced by subway tunnels. Energy tunnel technology based on heat pumps can not only solve the problem of thermal pollution but also realize the resource utilization of waste heat. However, the influence mechanisms of the tunnel air environment on the heat transfer characteristics of energy segments are still insufficiently studied. Taking the shield energy tunnel as the research object, this study proposed an energy segment model based on a capillary heat exchanger and established a fluid-thermal coupled numerical model on the COMSOL 6.4 simulation platform. Then, the effects of tunnel air temperature and speed on the heat transfer performance of the energy segment were systematically investigated. The results indicate that an increase in the temperature differential between the tunnel air and the inlet water of the capillary heat exchanger significantly enhances the heat transfer rate of the energy segments. Specifically, a 5 °C rise in air temperature corresponds to a 60.7% increase in the heat extraction rate of the CHE during the heating season, whereas it results in a 58.8% decrease in the heat release rate of the CHE during the cooling season. An increase in tunnel air speed enhances the overall heat transfer coefficient by strengthening convective heat transfer between the tunnel air and the energy segment. Although the enhancement of convective heat transfer is limited, the system already demonstrates relatively optimal heat transfer performance at a wind speed of 4.61 m/s. The study further reveals that increasing these two parameters not only enhances heat exchange but also exacerbates the non-uniformity of temperature distribution across the segment. This study conducts an in-depth analysis of how tunnel environmental parameters impact the thermal performance of energy segments, thereby offering a theoretical foundation for the optimized design of these energy segments in shield tunnels. Full article

In hot and humid regions, urban underground utility tunnels are susceptible to high temperature and humidity due to moist inlet air, cable heat dissipation, and limited ventilation jointly affecting the internal environment. To address this issue, an alternating ventilation strategy, in which fan operation is periodically reversed to switch between air supply and exhaust, is proposed. Compared to conventional mechanical ventilation, this strategy overcomes the constraints of unidirectional airflow and mitigates thermal and humidity stratification, with low retrofit requirements and good adaptability. Ventilation performance was evaluated using non-guarantee rates for temperature and relative humidity, i.e., the ratio of the number of measurement points where the temperature/relative humidity exceeds 40 °C/65% to the total number of measurement points in the utility tunnel (TNGR and RHNGR), non-uniformity coefficients (K_T and K_RH), and mean temperature (T_m). The alternating mode outperformed the conventional mode, reducing TNGR by 6.0% and Tm by 0.3 °C while improving temperature and humidity distributions and lowering cable temperatures. Although the reduction in T_m appears modest, it is practically meaningful because it helps weaken thermal stratification and local overheating, improves cable operating conditions, and may reduce the need for high-airflow operation when tunnel temperatures approach the permissible limit. Response surface methodology was further used to optimize the alternating ventilation parameters, indicating that the recommended fan commutation frequency is 2 under different inlet air temperatures. CFD validation confirmed the effectiveness of the optimized scheme. At an inlet air temperature of 35 °C, KRH decreased from 11.9% to 11.0% and Tm decreased from 37.5 °C to 36.9 °C. Full article

Near-bit multi-parameter MWD (measurement while drilling) is a key technology for achieving precise and efficient directional drilling in underground and tunnel engineering. The near-bit multi-parameter MWD method was studied, and a “center + side wall” distributed measurement scheme was proposed, based on an analysis of special application scenarios in underground and tunnel engineering. The transmission characteristics of Bluetooth wireless signals in water were investigated. An analysis of the underwater Bluetooth signal link was conducted. When the transmission distance is 100 mm, the received signal strength is −17.5 dBm, and the link margin is 69.5 dB. Wireless Bluetooth was used to transmit the near-bit data. A Bluetooth wireless communication simulation model was established using ANSYS software, and the influence of transmission power, transmission medium, and transmission distance on the Bluetooth signal strength was analyzed. The results indicate that: (1) the received signal strength increases with transmission power, and appropriately increasing the transmission power can improve the effect of Bluetooth wireless communication and extend the communication distance. (2) When the transmission medium is water, the received signal is unstable, and the echo loss curve shows a high and low oscillation form, presenting a frequency shift feature; when the transmission medium is air, the received signal is relatively stable, and the echo loss curve shows a parabolic form. The echo loss of Bluetooth wireless signal in water transmission is significantly higher than that in air transmission, indicating that the Bluetooth signal attenuates more rapidly when transmitted in water. (3) When the transmission distance increases near the optimal transmission frequency of 2.4 GHz, the echo loss increases accordingly, and the received signal strength of the wireless receiving module gradually decreases. The theoretical analysis, simulation, and indoor test results are in good agreement. The reasonable Bluetooth transmission power is 1 mW, and the transmission distance is 100 mm. After completing the overall scheme design and simulation analysis optimization, the structure, circuit, and program development were carried out, and the near-bit multi-parameter MWD device was developed. A laboratory water supply test was conducted, and the power supply, collection, and wireless transmission were all normal. A drilling test was carried out at an underground engineering of a coal mine in Wuhai City, achieving a drilling depth of 2328 m. A continuous and stable collection of various parameters such as WOB (weight on bit), torque, rotation speed, vibration, and gamma was carried out. A wireless transmission channel for near-bit data was established across the screw drilling tool. It can provide key technical support for the research and development of near-bit MWD in underground and tunnel engineering. Full article

This study numerically investigates the aerodynamic and thermal interactions between a full-scale metro train and the surrounding airflow within a confined tunnel environment using steady-state Reynolds-averaged Navier–Stokes (RANS) simulations. The six-car train, with a total length of 108 m and a cross-sectional area of 5.97 m², operates in a tunnel with a 9.83 square meter cross-section, resulting in a high blockage ratio of approximately 60 percent. The Shear Stress Transport (SST) k–ω turbulence model and a high-resolution finite-volume mesh comprising over 8.5 million elements were employed to capture detailed near-wall phenomena. Six representative motion scenarios were analyzed, including early acceleration, peak cruising, and deceleration phases, with realistic thermal boundary conditions applied by assigning the tunnel air temperature as 29.2 °C and the train surface temperature as 35.0 °C. Velocity, pressure, temperature, and turbulence kinetic energy distributions were extracted from both longitudinal and cross-sectional planes. In addition to visual contour assessments, pointwise and spatially averaged field data were examined to quantify the development of airflow structures, pressure distribution, and thermal behavior. The results reveal speed-dependent aerodynamic resistance, pronounced recirculation and stagnation zones around the train nose and tail, and variations in convective heat transfer rates that evolve with train velocity. These findings provide insights into tunnel ventilation design and thermal management for underground metro operations, representing a novel integration of full-scale computational fluid dynamics (CFD) with thermal characterization under realistic conditions. Full article

Rectangular shield tunnels demonstrate significant advantages in underground space utilization due to their optimal cross-section efficiency and enhanced spatial functionality. Furthermore, their shallow overburden construction capability minimizes environmental impact and preserves subsurface resources. However, compared with circular shield tunnels, rectangular configurations exhibit greater susceptibility to longitudinal differential torsional deformation under asymmetric external loading. This deformation mechanism may induce excessive stresses in segments and connecting bolts, potentially causing joint offsets at tunnel rings that compromise structural integrity. This paper proposes a computational method for determining the longitudinal equivalent torsional stiffness of rectangular shield tunnels under combined compression–bending–torsion loading based on an equivalent continuum model. The proposed novel theoretical solutions were systematically validated against numerical simulations through comparative analysis. Parametric studies revealed that the effective ratio of longitudinal torsional stiffness increases proportionally with segment width-to-height ratio and bolt quantity while exhibiting inverse correlations with segment thickness and bolt equivalent shear length. The effective ratio of longitudinal torsional stiffness is directly correlated with compression–torsion ratios and bending–torsion ratios, with different load combinations significantly influencing torsional performance. Consequently, design optimizations incorporating increased bolt pre-tension forces or pre-stressed segment structures are proposed to improve torsional performance in rectangular shield tunneling systems. Full article

Water and mud inrush represent some of the most catastrophic geological hazards encountered in tunnel engineering. Underground Magnetic Resonance Sounding (UMRS) holds significant potential for prospecting hydrogeological parameters within adverse geological bodies. The implementation of the method is limited, however, by the challenge of undesired frequency offsets between the assumed and true Larmor frequencies and poor signal-to-noise ratios in the tunnel environment. For the adaptation of UMRS to the tunnel environments, accurate modeling considering the off-resonance effects and magnitude enhancement of received signals is required. The traditional UMRS application assumes that on-resonance excitation is valid for any circumstance. Neglecting the effects of undesired frequency offsets produces a significant influence on amplitudes and phases of UMRS signals, as demonstrated by our models. Moving beyond the on-resonance excitation condition, we focus on a primary study of a novel multi-off-resonance excitation method using a broadband pulse, in which the off-resonance effects are exploited for improving signal magnitudes of UMRS. To implement the method we proposed, a new excitation pulse with several spectral peaks in a finite bandwidth is presented. Each spectral peak of the excitation spectrum contributes to the response voltage according to its spectral amplitude and offsets to Larmor frequency. The spectrum of the new excitation pulse can be modulated according to demands. The feasibility of the excitation pulse and method are supported by synthetic experiments using three different pulse parameters. Significant magnitude enhancement in the sounding curves is presented in the occurrence of undesired frequency offsets with different magnitudes. Furthermore, the method we proposed provides signal enhancement for the deeper water occurrence in the presence of an undesired frequency offset. We note that the present study is a theoretical and numerical proof-of-concept investigation. Experimental validation, including laboratory-scale physical model tests and field tunnel measurements, is planned as future work once suitable transmitter instrumentation becomes available. Full article

The Earth Pressure Balance (EPB) shield machine plays a pivotal role in underground tunnel excavation, where precise control of chamber pressure is essential for maintaining tunnel stability and minimizing risks. Traditional EPB control methods heavily rely on operator experience, resulting in delays and limited responsiveness to sudden geological changes. This paper presents an improved EPB mechanism model that builds upon traditional approaches, which primarily consider chamber pressure changes caused by soil volume variations. The improved model further incorporates the effects of excavation face pressure variations, arising from factors such as cutterhead soil extrusion and changing geological conditions. By integrating these additional influences, the model achieves more accurate predictions of chamber pressure. To further enhance performance, a hybrid modeling approach is proposed, combining the improved mechanism model with a data-driven component that compensates for residual prediction errors. The hybrid model is validated using field data from two distinct tunneling projects, demonstrating superior prediction accuracy and generalization capability compared to standalone mechanisms and data-driven models. The results confirm that the proposed hybrid model significantly improves pressure prediction accuracy and provides a more reliable solution for intelligent control of the EPB process. Full article

The safe service of tunnel inverted arch structures in high-altitude cold regions is heavily restricted by the performance of backfilling materials, which need to simultaneously adapt to low-temperature, low-pressure extreme environments and meet the long-term mechanical requirements of underground building structures. However, the strength development and preliminary mechanical applicability of foam concrete for tunnel inverted arch backfilling under reduced atmospheric pressure remain insufficiently understood. To this end, this paper carries out mix proportion optimization and mechanical performance testing of foam concrete, focusing on the strength behavior under different dry densities and simulated high-altitude low-pressure conditions. The test results show that the compressive strength of foam concrete is positively correlated with dry density, and the growth rate accelerates when the dry density is above 1000 kg·m⁻³. Specifically, the developed high-performance foam concrete with a dry density of 1200 kg·m⁻³ achieves a 28-day compressive strength of 27.1 ± 1.2 MPa under 60 kPa atmospheric pressure, indicating stable mechanical performance with low variability. The results indicate that, within the tested dry-density range and under the adopted curing and pressure conditions, the developed foam concrete can meet the basic compressive-strength requirement for tunnel inverted arch backfilling. This study provides a reference for material selection and structural design in high-altitude cold-region tunnel engineering and highlights the potential applicability of lightweight foam concrete in underground structures. Full article

Mine disasters require urgent lifeline setup in confined tunnels, but manual rescue in unstable accident zones carries huge safety risks. Coal mine rescue robots (CMRRs) have become key equipment to replace manual rescue. However, traditional remote-controlled CMRRs suffer from low autonomy and weak environmental perception capability, which have become critical bottlenecks for field application. As an emerging technology in the mining field, digital twin enables high-precision virtual-real mapping and on-site operation guidance, providing a novel solution to the above problems. To realize autonomous navigation and digital twin visualization of the CMRR, this paper first carries out targeted hardware retrofits on the CMRR platform, upgrades environmental perception, communication transmission and motion control modules, and lays a solid hardware foundation for subsequent algorithm design and system implementation. Aiming at the complex post-disaster underground environment, a digital twin-integrated CMRR system is constructed. For intelligent autonomous navigation, this study investigates a 3D point cloud–based autonomous navigation framework and proposes a slope-fitting method as well as a maximum arrival probability obstacle avoidance method based on Bézier curve trajectories. For environmental visualization, a digital twin interactive interface is built to monitor gas and other environmental parameters in real time, and accurately reconstruct underground roadway structures based on point cloud data. This design not only ensures the robot’s autonomous obstacle avoidance but also helps rescuers grasp underground conditions in advance. Field tests in a simulated post-disaster mine with complex terrain show that the system can stably complete autonomous navigation tasks, maintain stable motion control under dynamic interference, and provide accurate and reliable environmental data for rescue decisions, verifying its feasibility and effectiveness in harsh mine rescue scenarios. Full article

Underground mine tunnels are often characterized by extremely uneven illumination, weak surface textures, and frequent dynamic interference, which severely undermine multi-view photometric consistency and easily induce floating artifacts and spatial divergence in conventional vision-based 3D Gaussian Splatting (3DGS). To address these issues, we propose a LiDAR-guided 3DGS framework for underground tunnel reconstruction based on dynamic-object removal and differentiable unsigned distance field (UDF) regularization. First, a dynamic foreground removal strategy with background restoration is introduced to remove transient foreground disturbances and restore static supervision consistency. Second, LiDAR point clouds are leveraged to initialize Gaussian primitives with a reliable geometric skeleton in weak-texture regions. More importantly, LiDAR priors are further converted into a differentiable UDF field and serve as a persistent geometric constraint. A dual-track mechanism is designed, where continuous geometric attraction pulls mildly deviated Gaussians back toward the physical surface and periodic out-of-bound culling removes severely drifting primitives. Experiments on real underground tunnel and chamber scenes show a clear scene-dependent behavior of the proposed method. In the tunnel scene, the method achieves the best SSIM together with competitive PSNR and LPIPS, while also reducing redundant out-of-bound primitives and improving geometric cleanliness. In the chamber scene, however, its advantages under global full-reference metrics are less evident. These results suggest that the proposed LiDAR-guided and differentiable UDF-regularized framework is particularly beneficial for weak-texture tunnel environments, while further improvement is still needed for chamber scenes with more complex appearance variations. Full article