20 October 2026, Volume 22 Issue 5
    

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  • Coordination Assessment of Station Area Effectiveness Coupling Based on Node-Place Model
    Dai Peng, Cen Shi, Liu Zixuan, Fu Guannan, Wang Yanjun
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1541-1550. https://doi.org/10.20174/j.JUSE.2026.05.01
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    In the context of the continuous expansion of the metro network, it is imperative to enhance the quality of station areas. Evaluating the development status of the area around the stations, guiding the coordinated development of stations and cities, and improving the quality of urban space have become the key research issues in rail cities. Urban metro station area has the dual characteristics of “node” and “place”, this paper discusses the application and optimization expansion direction of the Node-Place model through the systematic retrospection and sorting out of the Node-Place model. Taking the 40 station areas of Qingdao Metro Line 1 as research samples, this paper constructs the “Node-Place-Coupling coordination” station area effectiveness assessment and classification model, comprehensively assesses the station area node and place effectiveness, and quantitatively analyzes the degree of coupling and coordination between the station area transportation function and the urban function development, it offers a sophisticated theoretical framework for evaluating and categorizing the effectiveness of station areas. Based on the assessment results, the current development status of station areas is classified into six major types, and comprehensive efficiency improvement strategies have been proposed for each type. The study explores an integrated optimization path for both above-ground and underground spaces, providing a replicable practical approach for optimizing similar urban rail transit station areas.
  • Robustness Evaluation of Urban Metro-based Underground Logistics System Considering Cascading Failures
    Liu Qing, Xu Yuanxian, Dong Jianjun, Sun Bo, Chen Zhilong
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1551-1562. https://doi.org/10.20174/j.JUSE.2026.05.02
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    With the gradual expansion of pilot implementations of metro-based underground logistics systems (M-ULS), research has largely focused on routine transportation scenarios. However, studies on network robustness under node failures remain limited, hindering the development of scientifically grounded planning strategies for stable operation. To this end, this paper designs the M-ULS operation process under cascade failure and proposes a network robustness assessment method. Firstly, the load redistribution process under node failure is analyzed, and the cascade failure model is constructed. Secondly, using the Nanjing multi-line passenger and cargo intermodal network as a case study, we assess the impact of key transfer node failures on network performance and propose strategies to enhance network robustness from a planning standpoint. The study reveals that factors including the volume of redistributed load, node location, and node functionality significantly affect network robustness. When the capacity of certain key transit nodes is reduced by 80%, the network's node failure rate can be as high as 22.7%, and the increase in unit transport time and cost for redistributed loads can reach 50.6% and 20.1%, respectively. The addition of direct connecting tunnels, the enhancement of node capacity, and the coordination of underground freight organizations can be potential strategies to improve the robustness of the network. These results not only extend the theoretical framework for M-ULS network design but also provide actionable decision support for maintaining stable system operation.
  • Enhancing the Resilience of Underground Space in Urban Schools from the Perspective of Evolutionary Resilience
    FanJiancai, Li Jialin, Tang Yao
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1563-1572. https://doi.org/10.20174/j.JUSE.2026.05.03
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    With the deepening of urban intensification in China, the increasing frequency of various urban emergencies poses significant threats and challenges to urban infrastructure, resource utilisation, and sustainable development. As an essential component of public urban space, the underground space of primary and secondary schools holds great potential for enhancing urban resilience. However, a range of issues—such as single-function usage, lack of regional coordination, underutilization of value, and outdated management concepts—have emerged during its development, hindering its integration into the broader framework of urban resilience construction. From the perspective of evolutionary resilience, this study employs the Analytic Hierarchy Process (AHP) to evaluate the value of underground campus spaces across six dimensions: functional redundancy, environmental adaptability, safety and reliability, facility completeness, traffic organisation, and intelligent responsiveness. Furthermore, the study conducts an empirical resilience assessment using the fuzzy comprehensive evaluation method on the underground spaces of three newly built secondary schools in Wuxi. Based on the evolutionary resilience perspective, the paper proposes resilience enhancement strategies in three areas: spatial layout and circulation planning, multifunctional and collaborative design, and intelligent and green design—aiming to contribute to the development of new paradigms and models for resilient urban spatial construction.
  • Three-Dimensional Evaluation of Safe Exploitation and Utilization of Underground Space: A Case Study of Zhuhai City
    Chen Kaiming, Chen Yuanfang, Wu Yadong, Liao Kunyan, Long Cuicui
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1573-1582. https://doi.org/10.20174/j.JUSE.2026.05.04
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    Soil mass in Zhuhai area is divided into 11 engineering geological standard layers of 4 types of soil, including artificial fill soil, inland alluvial sediment, quaternary sea-land intercross sediment and quaternary residual slope deposit in coastal plain area. The main layer of engineering geological layer of rock mass is divided into 13 engineering geological standard layers according to geological age (intrusive rocks according to intrusion stage and stage), combined with the sequence of new and old strata. According to the overall deployment of Zhuhai urban geological survey project, the basic geological models, engineering geological models and hydrogeological models of different regions and different precision are constructed by using 11295 standardized borehole data, geological maps, geological profiles and DEM data. The evaluation of underground space resources development and utilization based on 3D geological model is carried out to provide scientific basis for urban planning, construction and safe development and utilization of underground space resources.
  • An Elastoplastic Model of Clay Saturated with Saline Solution Considering the Influence of Osmotic Suction
    Wang Liye, Tan Zheng, Niu Yubo, Zhou Fengxi
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1583-1591. https://doi.org/10.20174/j.JUSE.2026.05.05
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    Owing to its unique adsorption properties, clay gradually becomes saturated with saline solution following seawater leaching and water-salt migration. The mechanical properties of clay subsequently change with saline solution infiltration. Accordingly, this paper reviews and analyzes existing studies to summarize the effects of osmotic suction on the compression behavior, preconsolidation pressure, and shear strength of clay saturated with saline solution. The results show that increased osmotic suction under chemo-mechanical loading induces particle agglomeration and flocculation, thereby increasing clay compactness, decreasing preconsolidation pressure, and increasing the internal friction angle. However, changes in the compression index depend on the loading method and clay mineral type, whereas the effect of osmotic suction on cohesion may be neglected to a certain extent. On this basis, a non-associated elastoplastic model for clay saturated with saline solution is established using osmotic suction as the chemical state variable and incorporating the concept of potential strength and the modified Hvorslev line. Finally, the model is validated using triaxial compression test results for Zhangye silty clay and Ennore marine clay at different osmotic suction levels. The results demonstrate that the model can predict the mechanical behavior of clay under complex chemical conditions.
  • Statistical Damage Constitutive Model of Rock Based on the Energy Storage Limit
    Su Lei, Guo Jianqiang, Wei Shiyan, Li Yu
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1592-1604. https://doi.org/10.20174/j.JUSE.2026.05.06
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    To address the low accuracy of traditional rock constitutive models, research from an energy perspective offers a method for enhancing their precision. Firstly, based on the fundamental cause of rock failure being the release of elastic strain energy, the intrinsic connection between elastic strain energy and rock strength was analyzed. Considering that the energy storage limit of rocks can predict their stress characteristics, a rock energy storage limit model incorporating confining pressure effects was constructed. Then, integrating statistical damage theory, a rock statistical damage evolution model based on the energy storage limit was established, and the method for parameter determination was provided. The influence of model parameters on the stress-strain curve was also discussed. Finally, verification using various rocks demonstrated that the newly established energy storage limit model accurately predicts the variation law of rock stress characteristic values, and the newly established statistical damage evolution model effectively simulates the rock deformation process. In terms of accuracy, it outperforms traditional research results, verifying the rationality and accuracy of the constitutive model and its ability to predict rock strength.
  • Loosening Earth Pressure of Shield Tunnel in Composite Stratum Considering the Influence of Seepage
    Zhao Yu, Dong Yacheng, Wu Yaojie, Shan Yao
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1605-1611. https://doi.org/10.20174/j.JUSE.2026.05.07
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    To investigate the variation in loosening earth pressure at the crown of shield tunnels in composite stratum under steady seepage conditions, the stress-deflection characteristics of differential soil slices within the loosening zone were analyzed based on the governing equation for steady seepage and the horizontal differential element method. According to the soil properties and groundwater level, the loosening zone above the tunnel was divided into three regions. A formula for calculating the lateral earth pressure coefficient considering the arching effect of the major principal stress was then derived, and an analytical solution for the water and earth pressure at the tunnel crown was further established and validated. The results show that under seepage conditions, the vertical load at the tunnel crown exhibits a U-shaped distribution in the horizontal direction. Seepage weakens the soil arching effect and consequently increases the water and earth pressure. The water and earth pressure at the tunnel crown increases nonlinearly with increasing tunnel burial depth, and a larger internal friction angle makes this nonlinear increase more pronounced. At the same burial depth, increasing the internal friction angle of the soil enhances the soil arching effect and thereby reduces the water and earth pressure at the tunnel crown. The proposed method can provide a theoretical reference for shield tunnel load design in practical engineering.
  • Theory and Analysis of Grout Diffusion Based on Tortuosity
    Chen Yang
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1612-1621. https://doi.org/10.20174/j.JUSE.2026.05.08
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    The random distribution of strata pores introduces tortuosity in seepage paths, affecting grout diffusion performance. To investigate the impact of tortuosity on grout diffusion, a Newtonian fluid hemispherical diffusion model considering seepage paths was developed. The proposed model was validated using COMSOL Multiphysics software. Furthermore, the effects of grouting direction, grouting pressure, water-cement ratio, temperature and strata permeability coefficient on grout diffusion were analyzed. Combined with grouting test, the influence of tortuosity on grout diffusion ability was further analyzed. The permeability and pore characteristics of the stratum were analyzed by permeability test and mercury injection test, and the influence of tortuosity on the diffusion capacity of the grout was analyzed in combination with the grouting test. The results indicate that: The proposed model accurately reflects the influence of tortuosity on grout diffusion. Tortuosity significantly reduces the diffusion distance and accelerates the dissipation of grout pressure. When the grouting direction aligns with gravity, the diffusion distance increases. Additionally, increasing grouting pressure, water-cement ratio, temperature and strata permeability coefficient all lead to greater diffusion distances, while also intensifying the impact of tortuosity on diffusion distance. The diffusion ability of grout in inhomogeneous formation is obviously weakened, and the influence of tortuosity will be increased.
  • Analysis of the Entire Process of Surrounding Rock Deformation in Soft Rock Tunnel Construction Considering Grouting Reinforcement
    Lai Yong, Yang Xiaodong, Wang Yanbiao, Zhang Shuai
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1622-1631. https://doi.org/10.20174/j.JUSE.2026.05.09
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    Grouting reinforcement is one of the key measures to timely and effectively control the large deformation of the surrounding rock of soft rock tunnels under the action of high ground stress. With the aid of the unified degradation model of post-peak stiffness and strength of rocks, the evolution analysis of the elastoplastic state of the surrounding rock throughout the entire process of excavation and support of soft rock tunnels under high ground stress was carried out based on the unified strength criterion. After verification with the finite difference software FLAC-3D. The results show that: (1) The entire process curve of longitudinal deformation of the surrounding rock in high ground stress soft rock tunnels can be divided into four stages, including the initial deformation stage, the rapid deformation stage I, the rapid deformation stage II, and the stable deformation stage. After grouting reinforcement,the deformation rate and total deformation of the surrounding rock in the rapid deformation stage II and the stable deformation stage have significantly decreased, and the percentage of load borne by the secondary lining has also decreased significantly; (2) The larger the values of softening modulus Mc, Mφ, ME, the whole process curve of longitudinal deformation of surrounding rock has little change in the fast deformation stage Ⅰ, and the larger the deformation rate and total deformation in the fast deformation stage Ⅱ and the stable deformation stage, the longer it takes for surrounding rock to reach the stable state; (3) Reducing the distance between bolts and increasing the thickness of shotcrete has little effect on the rapid deformation stage I in the whole process curve of longitudinal deformation of surrounding rock, but has a greater effect on the rapid deformation stage II and stable deformation stage. When the distance between bolts is less than 1.2 m and the thickness of shotcrete is more than 20 cm, the deformation control effect of surrounding rock is better; (4) Too early grouting will lead to insufficient stress release and excessive deformation in the surrounding rock in the later stage; too late grouting will lead to excessive final deformation of the surrounding rock and poor deformation control effect.
  • Calculation Method for Flow Resistance of Soft Soil Around a Pile Based on Bingham Fluid
    Wu Min, Zheng Jiayong, Jiao Gaofeng, Deng Tao, Liu Qijian
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1632-1640. https://doi.org/10.20174/j.JUSE.2026.05.10
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    Under large-area loading, the lateral displacement of deep and soft soil is often similar to fluid flow. The surrounding soil is considered as Bingham fluid to investigate the thrust computation of soft soil flow around the pile and its impact mechanism on the pile foundation. The analytical formula for the flow drag operating on the single pile during the internal slip of deep soft soil is constructed, drawing on the fluid properties of Bingham and the theory of fluid mechanics. Further, based on the assumption of the rectangular distribution of flow drag along the pile body, and the matrix transfer method, the conventional cantilever pile method is modified, and the response of a single pile body under field loading conditions is solved. The results show that: A linear relationship between the pile body flow drag and the product of the relative flow velocity of the soft soil and the coefficient of soil dynamic viscosity. The flow drag formula presented in this study offers considerable benefits over the conventional soil pressure technique in accurately predicting and representing the actual pile reaction. The calculated maximum horizontal displacement accuracy of a single pile is high, and the bending moment distribution of the pile body is in good agreement with the measured data. The relative error of the maximum pile bending moment is as low as 6.8%. The research results can provide references for calculating flow drag and pile body response in similar soft soil projects.
  • Study on the Deformation of Surrounding Rock and Load Calculation Method of Super-Large Span Shallow Buried Strata Biased Tunnel
    Yuan Feng, Li Xiaoyong, Chang Fugui, Zhang Jianjun, Wen Yuanping
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1641-1651. https://doi.org/10.20174/j.JUSE.2026.05.11
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    Aiming at the unclear characteristics of surrounding rock load distribution in large-span tunnels under strata bias, and the lack of theoretical discussion on the distribution law of surrounding rock pressure, this paper, based on the Chongqing Rail Transit Line 27 Ciqikou Station project, establishes numerical models of tunnels with different spans under stratigraphic bias by using the finite-difference software of FLAC3D, and combines the models with the strength reduction method to obtain the distribution law of the tunnel deformation and plastic zone of tunnels with different spans under stratigraphic bias. The results indicate that: The displacement of the tunnel vault exhibits a trend of increasing initially and then decreasing at spans of 14~28 m, while the left and right arch shoulders demonstrate distinct characteristics of asymmetric pressure. When the span reaches 20 m, the displacement of the tunnel vault reaches its maximum value, and the displacement difference between the left and right arch shoulders also reaches its peak. Additionally, this paper improves the existing load calculation theory for shallow-buried terrain bias tunnels by incorporating the strength theory of stratified rock, and proposes a calculation method for the surrounding rock load in super-large-span shallow-buried terrain bias tunnels based on the limit equilibrium method. The reasonableness of this method is verified through model test results.
  • A Method for Calculating the Lateral Pressure of Shield Tunnel in Soft Soil
    Lai Haoran, Zhang Dongmei
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1652-1664. https://doi.org/10.20174/j.JUSE.2026.05.12
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    Shield tunnel construction significantly affects pressure acting on segmental linings. Current load calculation methods usually simplify the value of lateral pressure and remain dependent on traditional theories such as Static or Rankine theory. Despite minor discrepancies between calculated and measured load values, the substantial difference in load distribution patterns is the primary factor leading to inaccurate predictions of segmental deformation characteristics. To address this, this study first establishes soil displacement functions that account for stratum loss, synchronous grouting and tunnel deformation. Subsequently, upon introducing the nonlinear relationship between soil displacement and lateral earth pressure coefficient, a calculation formula for displacement-dependent nonlinear lateral pressure is derived using a resultant force equivalent method. Finally, a refined tunnel load calculation model is presented based on the modified routine method. The model's rationality is verified through field monitoring and physical model experiments. The research findings indicate that: In soft soil layers, given constant tunnel depth and grouting pressure, the relationship between the pressure at the arch barrel and the arch crown can be determined by the layer loss rate, and the qualitative circumferential load distribution can be evaluated using stratum loss ratio η: smaller η values favor circular distributions, whereas larger η values result in vertically elliptical distributions. The lateral pressure increases linearly with the increase of the grouting pressure difference. The change in grouting pressure at the arch barrel is greater than 1 in terms of pressure conversion rate, particularly under low η. Tunnel depth changes primarily influence lower semicircle lateral pressure. The pressure ratio between the arch barrel and the arch crown decreases as the burial depth increases. Furthermore, lateral pressure decreases significantly as soil resistance coefficient increases rises, especially in soft soils. The research results can provide a reference for the calculation method of loads in shield tunnels.
  • Research on the Deformation Coordination Mechanism of Plain Concrete Pile in Foundation Secant Pile
    Jiang Wenhao, Wu Qiongjun, Wu Jian, Chen Yuqi
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1665-1673. https://doi.org/10.20174/j.JUSE.2026.05.13
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    Current foundation pit designs for secant pile support structures universally neglect the deformation resistance of plain concrete piles, considering them solely for their waterproofing function. To investigate the deformation compatibility mechanism of plain concrete pile within secant pile support systems, this paper derives a method for calculating the force-deformation behavior of secant pile that accounts for plain pile stiffness.Initially, based on the working mechanism of secant pile and their mechanical characteristics under varying bending moments, force-deformation calculation formulas were derived. Subsequently, a calculation method for determining the percentage contribution of plain pile to the overall secant pile stiffness was established, quantifying their stiffening effect. The method was then applied to an engineering case study. Verification and comparative analysis were performed using Z-soil finite element analysis software. Horizontal displacement calculation results indicate that this method enhances stiffness by approximately 20.66% compared to current specifications, demonstrating the necessity of considering plain pile stiffness. Furthermore, theoretical calculations, numerical simulations, and field monitoring data show good agreement, confirming the method's ability to accurately describe the mechanical behavior of plain concrete piles within secant pile walls.Finally, employing the controlled variable method within this study's engineering context, a detailed analysis of plain pile parameter variations was conducted. This analysis revealed the influence patterns of secant overlap, pile diameter, and material strength changes on the horizontal displacement of secant pile.
  • Molecular Dynamics Simulation Study on the External Surface Hydration of Sodium Montmorillonite
    Wang Yuepeng, Tang Shibin, Liu Xiangjun
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1674-1683. https://doi.org/10.20174/j.JUSE.2026.05.14
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    To reveal the hydration mechanism on the external surface of sodium montmorillonite, this study combined Monte Carlo and molecular dynamics simulation to systematically explore the hydration evolution characteristics of sodium montmorillonite under different burial depths. The results show that as the water molecule coverage increases, the total energy of the system decreases, the potential energy significantly reduces, while the kinetic energy gradually increases. Compared with the surface conditions, the total energy and kinetic energy of the system increase under deep burial conditions, while the trend of potential energy is different. Water molecules extend outward through the hydrogen bond network, and Na+ migrates along with them. The thickness of the interface water layer increases with the increase in coverage rate, and it is even thicker under deep burial conditions. The distribution of Na+ atomic concentration is complex and is influenced by coverage rate and burial depth. Except for the single-peak structure of Ow-Ow, the radial distribution functions of other atoms exhibit a bimodal characteristic, and the peak values change with burial depth. The self-diffusion coefficient of water molecules is higher than that of Na+. Under deep burial conditions, the diffusion of water molecules and Na+ is enhanced, and Na+ exhibits coverage-dependent behavior. The research results can provide a molecular-scale theoretical basis for understanding the hydration mechanism of deep montmorillonite and optimizing drilling fluids.
  • Semi-Supervised Classification of Tunnel Face Lithology Based on Feature Enhancement
    Zhang Ming
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1684-1693. https://doi.org/10.20174/j.JUSE.2026.05.15
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    In tunnel engineering, lithology classification from the excavation face is vital for ensuring construction safety and efficiency. However, traditional machine vision methods often struggle with limited labeled data and the high cost of manual annotation, especially when dealing with diverse and complex geological conditions. To address these challenges, this study proposes a novel approach that combines generative adversarial networks (GANs) with semi-supervised learning to build a robust lithology classification model. First, a comprehensive lithology database was constructed, encompassing 12 typical rock types observed on tunnel faces. To overcome the scarcity of training samples, a Conditional Generative Adversarial Network (CGAN) was introduced for deep feature enhancement, transferring the generation target from the pixel space to the feature space extracted by a convolutional neural network. This enabled the generation of multi-scale features with strong geological discrimination. To further utilize both limited labeled data and a large quantity of unlabeled data, a Semi-supervised GAN (Semi-GAN) was implemented, allowing its discriminator to simultaneously judge the authenticity of inputs and classify lithology types, while its generator synthesizes additional feature samples to expand the feature space. By integrating CGAN-based feature augmentation with Semi-GAN training, the proposed method significantly improves lithology classification performance. In testing, the model achieved an overall accuracy of 93.3%, representing a 7.7% improvement over traditional classification methods. The results demonstrate that the proposed approach effectively mitigates data scarcity and annotation burdens, providing a promising solution for intelligent lithology classification in tunneling and other subsurface engineering applications.
  • Study on the Mechanism of Crack Initiation and Propagation in Granite with Single Fissure
    Wang Zhao, Xie Licheng, Hu Cong, Wang Haiquan, Shi Guangbin
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1694-1704. https://doi.org/10.20174/j.JUSE.2026.05.16
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    The initiation and development of microcracks inside rocks are the essential reasons for strength weakening and failure. In order to explore the mechanism of crack initiation and propagation in rock, the law of crack strength, initiation angle and evolution in granite with single crack was studied by means of laboratory tests, discrete element numerical simulation and theoretical analysis. The results show that: (1) The rock strength decreases first and then increases with fracture inclination angle, and reaches the lowest value around 45°. The wing crack initiation angle increases with the increase of inclination angle. (2) Friction coefficient inhibits the propagation of wing cracks, and the crack initiation stress, as well as peak stress increase with the increase of the friction coefficient. However, the wing crack initial angle gradually decreases with the increase of friction coefficient. (3) Based on the maximum tangential tensile stress criterion, the crack propagation condition and crack initial angle of rock with single fracture were derived. It is found that the variation of crack initial angle with inclination angle is consistent with the experimental and numerical results. (4) When the inclination angle is less than 45°, the crack initial angle decreases with the increase of friction coefficient, and in the case of greater than 45°, the crack initial angle increases with the increase of friction coefficient. The results are helpful to understand the degradation and failure mechanism of fractured rock mass.
  • Experiment on Stress Interference Effects in Multi-Staged Fracturing on Fracture Propagation
    Tang Jiren, Liu Chenlong, Jia Yunzhong, Huai Qisi, Gong Tianyi
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1705-1717. https://doi.org/10.20174/j.JUSE.2026.05.17
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    The multi-staged fracturing technology for horizontal wells significantly enhances reservoir modification effect in unconventional oil and gas reservoirs by performing multiple hydraulic fracturing stages along the horizontal section. To investigate the effects of fracturing sequence and stage spacing on fracture initiation and propagation, the research utilized a large-scaled true triaxial fracturing and seepage simulation system to conduct a segmented hydraulic fracturing test on a 300 mm×300 mm×300 mm cubic sample. The results indicate that: Fractures created during earlier stages form an induced stress field. When the induced stress superimposes with the in-situ stress, the increased local stress leads to a rise in fracture initiation pressure. The reciprocating fracturing can effectively mitigate this stress superposition effect, thereby reducing the fracture initiation pressure to some extent. Meanwhile, compared to other fracturing methods, reciprocating fracturing offers greater advantages in promoting uniform propagation of fractures along the fracture surface. Under reciprocating fracturing conditions, when the fracture spacing is moderate, the induced stresses generated by the two initially fractured wings on either side act in opposite directions, promoting straighter propagation of the central fracture while allowing it to extend beyond the length of the first two fractures. The research findings are of significant importance for clarifying the stress interference mechanisms between fractures, optimizing fracture networks, and enhancing reservoir stimulation efficiency.
  • Direct Shear Testing and Numerical Simulation of Shear Behavior at Rock Anchorage Interface
    Li Yonghai, Fan Hongwei, Cen Feng, Shi Yankun, Wei Bohao
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1718-1726. https://doi.org/10.20174/j.JUSE.2026.05.18
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    Rock anchor structures are increasingly utilized in domestic engineering construction due to their advantages of minimal excavation, cost-effectiveness, low environmental impact, and construction efficiency. The determination of shear strength parameters at the interface between rock anchor, concrete, and rock has become critically important. This study focuses on the rock anchor system of the Xihoumen Rail-cum-Road Bridge, employing a combined approach of in-situ direct shear tests and numerical simulations to systematically investigate the shear behavior of the concrete/dacite interface. The results demonstrate that the τ-σ relationship curve for the interface between concrete and slightly weathered dacite under natural conditions exhibits strong regularity. The peak shear strength parameters were determined as f′=1.29 and c′=1.44 MP, while the shear strength parameter f=0.66. Numerical simulations revealed that specimen failure manifested as fully penetrated shear failure along the interface. As the normal load increased, significant deformation occurred in the dacite, with displacement propagation extending deeper into the rock mass. During shearing, the maximum shear stress concentration initially formed on the right side of the interface and gradually propagated leftward until complete penetration, ultimately leading to interfacial shear failure accompanied by stress release. The simulated strength envelope closely aligns with experimental curves obtained from field tests. These findings deliver essential geotechnical parameters for optimizing the stability analysis and structural design of the rock anchorage system in the Xihoumen Rail-cum-Road Bridge.
  • Study on Friction Effect of Rock Pipe Jacking under Acid and Alkali Conditions in Karst Geology
    Zhang Wenqiang, Li Chao, Zhong Zuliang, Peng Xianfeng
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1727-1738. https://doi.org/10.20174/j.JUSE.2026.05.19
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    In the process of rock pipe jacking construction in karst area, the influence of acid and alkali environment leads to the change of slurry lubrication performance, which aggravates the engineering problem of friction resistance. Based on the Guanjingkou Water Conservancy Project in Chongqing, the influences of slurry type, viscosity, pH value and mixing ratio of karst slurry on the friction characteristics of pipe-rock interface are systematically explored through indoor direct shear friction test and orthogonal design. The results show that: The lubrication performance of polymer mud is better than that of traditional mud, and too high or too low viscosity affects the lubrication effect. Compared with the weak alkaline conditions, the acidic environment will destroy the hydration film and increase the friction coefficient. With the increase in the proportion of karst water, the mud lubricity will be significantly reduced. According to SEM analysis, it is found that particle agglomeration, hydration film rupture and pore structure change are the main reasons for the decrease of slurry lubrication performance. Finally, by comparing the predicted friction resistance with the monitoring data, the reliability of the test is verified, which provides theoretical support and engineering guidance for the mud performance and friction control of pipe jacking engineering in karst area.
  • Analysis and Experimental Study on Rock Breaking Performance of Impact-Scraping Composite PDC Bit
    Ren Haitao, Chen Yixin, Wei Xiuyan, YangYingxin, Ji Guodong
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1739-1748. https://doi.org/10.20174/j.JUSE.2026.05.20
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    PDC bit is widely used in drilling engineering due to their rock fragmentation mechanism based on cutter invasion and scraping. However, drilling complex and challenging formations characterized by high hardness, strong plasticity, and high abrasiveness often results in ineffective cutter penetration or accelerated wear due to excessive rock-breaking energy consumption. This significantly compromises bit service life and drilling efficiency. The technical concept of composite percussive-rotary rock breaking proposes the independent yet synergistic application of impact and cutting mechanisms. Impact loads directly applied to the rock induce pre-fracturing, thereby reducing rock drilling resistance and creating favorable conditions for efficient bit cutting. This study analyzes the influence of rock properties, weight on bit (WOB), and rotational speed on rock-breaking performance through comparative experiments. Results demonstrate that:Under equivalent speed or the same drilling pressure, the composite percussive-rotary PDC bit exhibits lower measured torque compared to a conventional PDC bit, accompanied by a 33.93% reduction in mechanical specific energy (MSE). The findings present a promising rock-breaking tool for significantly enhancing the rate of penetration (ROP) in typical complex and difficult-to-drill formations. This approach offers a novel solution for improving the speed and efficiency of deep and ultra-deep oil and gas drilling operations in China.
  • Experimental Study on Stress Redistribution of Surrounding Rock in Loess Tunnel
    Li Yao, Du Xuchao, Guo Zhanglong
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1749-1760. https://doi.org/10.20174/j.JUSE.2026.05.21
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    Based on the practical engineering geological conditions of the Luochuan Tunnel, the mechanical response characteristics of the surrounding rock of the loess tunnel under different burial depths were studied through model tests. The relationship between the material parameters of surrounding rock, sprayed concrete, steel frame, and advanced small guide pipes is determined using similarity theory. Combining prefabricated support with 3D printing technology, a three-step support rapid assembly system is established to accurately simulate the stepwise excavation and support sequence effects.For different burial depth conditions, conduct an in-depth analysis of the stress redistribution in the surrounding rock and the evolution of the soil arch.The results show that: (1) During the three-step excavation process, the stress redistribution in the surrounding rock exhibits a staged characteristic. Before excavation at the monitoring section, an unloading zone first forms at the arch crown, followed by the formation of the soil arch effect above it. When the upper step is excavated, the soil arch effect is significantly enhanced. After the completion of the invert support, the soil arching effect gradually stabilizes. (2) As the burial depth increases, the height of the soil arch increases, and its shape evolves from a flat arch to a triangular arch, with an uplifted crown and increased curvature, thereby enhancing the soil arch effect. (3) The vertical stress in the surrounding rock at the arch crown, as observed in the model test, continuously decreases under the influence of the soil arch. However, in practical engineering, the surrounding rock pressure continues to increase, and the two values converge when they stabilize. In practice, the surrounding rock pressure measured in the field tends to be lower due to the initial deformation and settlement of the support. In contrast, the internal stress of the surrounding rock obtained from model experiments provides a better analysis of the stress redistribution patterns.
  • Analysis of the Stress Characteristics of PCCP under Pipe-Water-Soil Coupling Action
    Cui Jiaming, Hu Wenbo, Xing Guohua, Miao Pengyong
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1761-1773. https://doi.org/10.20174/j.JUSE.2026.05.22
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    To investigate the stress characteristics of prestressed concrete cylinder pipe and joint under multiple effects such as working internal pressure, water weight, external soil pressure, and differential settlement during service, a refined three-dimensional finite element model of the pipe-water-soil is established considering the coupling of pipe-liquid fluid-solid coupling and the interaction between pipe and soil. The model was validated using experimental results, and the effects of internal pressure, burial depth, and settlement on the stress characteristics of the PCCP pipe body and joint were analyzed. The results show that: The working internal pressure (0~0.6 MPa) activates the circumferential constraint effect of the prestressed concrete cylinder, forming an “active resistance mechanism”. In the 0~0.4 MPa stage, the internal pressure counteracts the circumferential tensile stress generated by external loads, reducing the stress of the socket by 19.2%. After exceeding 0.4 MPa, the steel cylinder and concrete deform synergistically into a nonlinear stage, and the stress redistribution of the socket presents an elliptical characteristic, with the stress concentration factor reduced to 1.8, proving the strengthening effect of internal pressure on the overall structural integrity. The overlying soil pressure causes the arching effect of the soil around the pipe, resulting in an asymmetric distribution of stress on the pipe body. For every 1m increase in burial depth, the top pressure stress of the pipe increases by 12.7%, while the stress increase at the pipe waist is only 7.3% due to the lateral constraint of the soil. This differential deformation is the main cause of the elliptical deformation of the pipeline. When the settlement difference reaches 2% of the pipe diameter, a significant moment redistribution phenomenon occurs at the contact surface of the socket. Mechanical analysis shows that the stress concentration factor in the upper compression zone of the interface reaches 2.4, and a 3.2 mm interface separation occurs in the lower tension zone. This tension compression coupling effect is the fundamental reason for the peak stress of 33.6 MPa. Further research has found that the stress relaxation effect of the rubber sealing ring of the socket will accelerate this failure process. The research results provide certain theoretical support for the operation and maintenance of PCCP pipelines during their service life.
  • Numerical Simulation on the Morphology of Hydraulic Fracture Propagation in Layered Shale
    Zeng Bo, Zhou Lei, Huang Haoyong, Chen Yi, Chen Liqing
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1774-1785. https://doi.org/10.20174/j.JUSE.2026.05.23
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    The propagation paths and morphological evolution of hydraulic fractures in shale are significantly influenced by layered interfaces, and the underlying interaction mechanisms and governing principles require further investigation. In this study, numerical simulations were conducted to model the propagation morphology of hydraulic fractures in shale containing multiple bedding planes. The results indicate that: (1) bedding planes affect both the vertical and horizontal propagation of fractures. The larger the opening area of the bedding planes, the greater their capacity to confine fracture height. Furthermore, increased normal stress across the bedding planes, combined with lower permeability, enhances their ability to restrict fracture length along the bedding interfaces. (2) The initiation of fractures along bedding planes is positively correlated with the fluid injection rate and fluid viscosity. In contrast, the extent of fracture propagation is inversely correlated with these parameters, as well as with the strength of the bedding planes. (3) The primary factors influencing fracture initiation in horizontal and inclined bedding planes are elevated fluid pressure and high fluid flow rates, respectively. To alleviate the stress shadow effect and the limitations on fracture height imposed by the bedding planes, appropriately reducing fluid injection rates or viscosity may promote the development of a more complex fracture network. Based on these findings, we propose an optimized hydraulic fracturing technique that employs alternating high and low injection parameters—both in terms of injection rate and viscosity—to maximize fracture volume and promote the development of fracture networks. This approach provides theoretical support for the efficient exploitation of shale gas resources.
  • The Deterioration Mechanism and Modification Technologies of Tunnel Shotcrete
    Ding Miao, Liang Ninghui, Wang Lijun, Sun Weizhe, Zhu Pengcheng
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1786-1803. https://doi.org/10.20174/j.JUSE.2026.05.24
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    Shotcrete is a core component of tunnel support systems; however, it is susceptible to deterioration in complex environments, which directly compromises the safety and stability of tunnel structures. To provide a systematic understanding of the current status and development of research on shotcrete deterioration in tunnels, this paper presents a comprehensive review from three perspectives: deterioration-inducing factors and mechanisms, research methods, and deterioration evaluation indicators. In addition, modification measures for tunnel shotcrete exposed to adverse environments are summarized, and directions for future research are proposed. The main conclusions are as follows: (1) The factors and mechanisms governing shotcrete deterioration under single- and dual-factor conditions have been largely clarified, whereas deterioration behavior under multifactor coupling requires further investigation. (2) The differences in the deterioration mechanisms of shotcrete and cast concrete mainly arise from the use of accelerators and the spraying process. (3) Experimental investigation, numerical simulation, and theoretical analysis are the principal methods used to study shotcrete deterioration, and their integrated application has become the predominant research approach. (4) The indicators used to evaluate shotcrete deterioration are relatively comprehensive and can be classified into apparent, mechanical, and microscopic indicators; however, the establishment of a complete evaluation system still requires further consideration. (5) Shotcrete modification primarily involves optimizing the mix proportions, developing new materials, improving accelerators, and refining the spraying process. Developing comprehensive modification strategies for shotcrete exposed to adverse environments will be a key direction for future research.
  • Research on the Stability of Compressed Air Energy Storage Caverns with Cushioning Layers
    Wu Zhaofeng, Wang Yingchao, Wang Wenbo, Zhou Wei, Wang Yingchao
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1804-1813. https://doi.org/10.20174/j.JUSE.2026.05.25
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    Under the long-term cyclic loading of high internal pressure, the surrounding rock of Compressed Air Energy Storage (CAES) caverns constructed in abandoned coal mine soft rock formations is prone to failure and instability, while the lining is highly susceptible to cracking. To meet the long-term operational safety requirements for soft rock CAES caverns and their structures, a novel composite structural design concept incorporating a cushioning layer is proposed. To investigate the influence of the cushioning layer on cavern stability, numerical simulations were employed to analyze the effects of cushioning layer thickness and the shear characteristics at the cushioning-lining interface on the stress-deformation behavior of the soft rock cavern and its structural components. Furthermore, a segmented lining structural design was introduced to specifically address the issue of excessive tensile stress in the lining. The results demonstrate that: increasing the cushioning layer thickness significantly improves the stress-deformation state of the surrounding rock, reducing displacement and stress to 3.7% and 10% of their original values, respectively. However, lining displacement increased by 71.4%. Changes in the interfacial shear characteristics exert a greater influence on the structural components than on the surrounding rock, with the cushioning layer and lining exhibiting opposite trends in their responses. The segmented structure effectively improves the stress distribution within the lining of the soft rock CAES cavern, thereby mitigating the risk of lining cracking. These findings hold significant practical implications for ensuring the long-term stability and structural design of CAES caverns constructed in soft rock formations of abandoned coal mines.
  • Research on the Dynamic Response Mechanism of Adjacent Underground Utility Tunnel under the Influence of Metro Operation Vibration
    Xu Qiang, Du Jingshan, Wu Shaoyan, Chang Shuguang, Xiao Fei
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1814-1828. https://doi.org/10.20174/j.JUSE.2026.05.26
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    Due to limitations in site conditions,linear projects may not be able to avoid adjacent disturbances,and the vibration of metro may have a dynamic effect on underground utility tunnel.This paper adopts the method of vibration test and numerical simulation based on the actual engineering background of Xi'an Kunming Road Underground Utility Tunnel and Metro Line 5 to study the vibration impact of metro operation on adjacent underground utility tunnel.The results indicate that the dynamic response of the internal structure of the utility tunnel will show the vibration amplification effect in the direction of less displacement limitation. The vertical acceleration peak value of the measuring point in the middle of the utility tunnel floor is about 24.3% higher than that of the measuring point closest to the metro on the south side of the floor. The amplification effect of the dynamic response of the steel structure support is more significant.The vertical acceleration peak at the center of the hollow steel support is about 37.7% higher than that at the junction of the south side of the hollow steel support and the sidewall of the utility tunnel. Except at measuring point 4, the vertical acceleration of the concrete buttress is higher than the horizontal acceleration.The dominant frequency band of the vertical and north-south dynamic response of each measuring point is the middle frequency band (30~70 Hz ).
  • Analysis of Surrounding Rock Excavation Response of Tunnel Crossing Fracture Zone
    Zheng Aichen, Liu Xingchen, Huang Feng, Yang Dong, Wan Guoqing
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1829-1839. https://doi.org/10.20174/j.JUSE.2026.05.27
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    To address the stability problem of surrounding rock in tunnels traversing fractured zones, this study investigates the mechanical response using scaled model tests and coupled PFC3D-FLAC3D numerical simulations. Results indicate that slip displacement within the fracture zone induces significant stress redistribution within a 1D (tunnel diameter) range on both sides of the zone, expanding the excavation-affected area by 25% compared with homogeneous strata. The displacement field exhibits marked discontinuities at the fractured-zone interfaces, with surrounding-rock convergence and face extrusion concentrated at the intersection of the fracture zone and the tunnel. Slip modes are governed by vertical displacement differences across the fracture zone. When excavation progresses from the footwall to the hanging wall, the slip mode transitions from reverse slip (slip-surface dip angle > fractured-zone dip angle) to forward slip (slip-surface dip angle < fractured-zone dip angle). Maximum surrounding-rock convergence occurs in the fractured-zone segment and is negatively correlated with fractured-zone thickness (5~15 m) but positively correlated with dip angle (30~90°). Excavation from the footwall to the hanging wall (along the dip direction) enhances surrounding-rock stability. These findings provide a theoretical basis for safety control during tunneling through fractured zones.
  • Mechanical Response Analysis of Tunnels Crossing Active Faults Based on Kerr Foundation Model
    Hui Qiang, Gao Feng, Du Pengcheng, Xiong Chaoyang, Tan Xukai
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1840-1852. https://doi.org/10.20174/j.JUSE.2026.05.28
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    In order to study the longitudinal deformation and mechanical response of tunnel under the action of fault dislocation, an analytical model considering the horizontal and vertical dislocation of fault is proposed. The tunnel is simplified as Timoshenko beam placed on Kerr three-parameter foundation model, and the local site displacement under fault dislocation is obtained by combining the dislocation theory. The ground displacement at the tunnel axis is transformed to the horizontal and vertical additional loads imposed on the tunnel. Based on the boundary conditions, the analytical models of vertical deformation and internal force of the tunnel are obtained by finite difference method. The accuracy of the models is verified by numerical simulation and existing theoretical models. Based on the established analytical model, the influences of fault dip angle, tunnel diameter and tunnel depth on the deformation and internal force response of the tunnel structure are further discussed. The results show that: Compared with the Pasternak model and the Kerr model without considering the horizontal additional load, the calculated results of the established model are closer to the numerical simulation results, and the bending moment calculated by the analytical model is larger when the horizontal fault component is not considered. With the increase of fault inclination Angle, the area affected by the fault becomes smaller, while the tunnel bending moment and shear force in the area gradually increase, and the axial force gradually decreases. Under the action of large fault dislocation, the vertical displacement values of tunnels with different diameters are close, but the longitudinal internal forces of the structure are significantly different. Affected by the stiffness of the foundation and the pressure of the upper surrounding rock, the greater the buried depth of the tunnel, the smaller the vertical displacement and the internal force of the structure.
  • Study on the Optimization Range of TBM Excavation Parameters under Different Rock Mass Classes
    Jiang Yue, Zhou Xiaoxiong, Gong Qiuming, Liu Yangyang, Xu Jianshu
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1853-1861. https://doi.org/10.20174/j.JUSE.2026.05.29
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    The tunneling performance of a hard-rock tunnel boring machine (TBM) is jointly governed by rock mass properties and TBM operating parameters. Therefore, using field tunneling data to investigate the relationships between operating parameters and tunneling performance under different rock mass classes is of great significance. Based on a water diversion tunnel project in Xinjiang, data with relatively reliable rock mass classifications were selected from the interval between the lower and upper percentile thresholds of the specific rock mass boreability index (SRMBI) distribution. The relationships of operating parameters with advance rate and specific energy were then analyzed for different rock mass classes, and optimal ranges of cutterhead rotational speed and penetration per revolution were proposed. The results indicate that, when the effects of operating parameters on both advance rate and specific energy are considered, the recommended operating parameters are as follows: under Class II rock mass conditions, the cutterhead rotational speed and penetration per revolution should exceed 6 r/min and 2 mm/r, respectively; under Class III rock mass conditions and geologically favorable Class IV conditions, the cutterhead rotational speed should be 5~6 r/min, and the penetration per revolution should exceed 9 mm/r; in sections with adverse geological conditions, the cutterhead rotational speed and advance rate should be below 4 r/min and 1.8 m/h, respectively. These results provide theoretical guidance for efficient TBM tunneling.
  • Study on the Reasonable Clearance of Small Clearance Mudstone Tunnels Considering the Rock Mass Damage Characteristics
    Xu Zhaoyun, Yang Wenbo, Li Haoyu, Xu Wenyu, Yang Qiaowei
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1862-1875. https://doi.org/10.20174/j.JUSE.2026.05.30
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    To investigate the deformation characteristics and mechanical properties of smallsmall-clear-distance mudstone tunnels, a tunnel in Chongqing was taken as the engineering background. Through model tests, the tunnel damage, settlement deformation, stress of surrounding rock, and steel arch support force were analyzed after tunnel excavation, and the sensitivity of the rock mass to damage in different burial depths, inter-spur distances, and offset distances was studied. The results show that:The sensitivity of the surrounding rock damage in small-clear-distance tunnel is more affected by burial depth than by clear distance and offset distance. Based on this, a deteriorated damage constitutive model was established using FLAC3D software to study the inter-rock damage in small inter-spur tunnels under different burial depths and inter-spur distances. Based on the damage zone, deformation modulus, and weakening of cohesion, different minimum safe inter-spur distances were determined. Using a subjective-objective combination weighting method based on game theory, a formula was obtained for the minimum safe inter-spur distance in small-clear-distance tunnels at different burial depths.
  • Simplified Quantitative Research of TBM Equipment Selection
    Fu Minghuan, Yu Jianping, Xu Yikang, Zheng Guobing, Wu Lei
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1876-1894. https://doi.org/10.20174/j.JUSE.2026.05.31
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    Research on the quantitative selection of TBM equipment is limited, and the corresponding calculation processes are often complex with poor generalizability. To reduce the workload, a simplified quantitative model for TBM selection is established to provide technical support for the preliminary selection of open TBM, single-shield TBM, and double-shield TBM. This approach enables the quantitative selection process to be extended from high-level research institutes to general production and technology departments. Based on existing research results, analyze and compare the commonly recognized factors affecting TBM excavation adaptability and safety adaptability, and screen out five key influencing factors for TBM selection. The membership functions and influence weights for TBM equipment selection influencing factors are constructed, and the fitness of various types of equipment is qualitatively calculated through a fuzzy mathematical evaluation model. The results show that: The weight order of the key influencing factors of open TBM is width of fracture zone= compressional deformation of the surrounding rocks > uniaxial compression strength of rock >water inrush>rock integrity coefficient, and the shield TBM is compressional deformation of the surrounding rocks> width of fracture zone> uniaxial compression strength of rock> water inrush> rock integrity coefficient. The type selection membership is trapezoidal of uniaxial compression strength of rock and the rock integrity coefficient, and the width of fracture zone and the water inrush are in a descending semi-trapezoidal distribution. The compressional deformation of the surrounding rocks is in an ascending semi-trapezoidal distribution. The accuracy of the model proposed in this paper is verified by practical engineering, demonstrating high accuracy and versatility.
  • Analysis and Control Research on Construction Stability of Multi-arch Tunnel without Middle Drift
    Tuo Mingxing, Peng Zhihao, Deng Zhiyun, Liu Baoguo, Chen Junwu
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1895-1908. https://doi.org/10.20174/j.JUSE.2026.05.32
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    The multi-arch tunnel without middle drift is widely used due to its high construction efficiency and excellent space utilization. However, during large-section excavation, challenges such as surrounding rock stability, stress transformation, and the impact of subsequent tunnel blasting on the preceding tunnel structure become critical. Therefore,this study systematically analysis the structural characteristics, construction difficulties, and technical challenges of the double-arch tunnel without middle drift, proposing control measures, including optimized blasting schemes, adjusted excavation methods, and tunnel structure design. Results indicate that:The main issues in the construction of such tunnels center on complex stress transformation during large-section excavation, surrounding rock stability control, and the impact of subsequent tunnel blasting on the preceding tunnel. Large-section excavation faces challenges like complex stress transformation and difficulties in controlling surrounding rock stability, particularly the impact of subsequent tunnel blasting on the preceding tunnel and the complex forces on the middle wall, which require ensuring its strength, stiffness, and rational structural form. To ensure stability during construction, strict control of the construction step distance and excavation scheme of the subsequent tunnel is necessary, along with enhancing the overall strength and stability of the tunnel, with special attention to the middle wall junction. Attention should be paid to the load distribution characteristics and stress transformation mechanism of multi-arch tunnels without central guide, revealing the laws of mechanical behavior to optimize structural design schemes. In terms of blasting vibration, optimizing blasting schemes, improving excavation methods, and adjusting propagation paths can reduce the impact of blasting on the tunnel structure, improving construction efficiency and safety. However, further research is needed on the vibration response characteristics of the middle wall and the secondary lining of the preceding tunnel, as well as on isolation layer schemes. Furthermore, integrating artificial intelligence into double-arch tunnel construction without middle drift, utilizing image recognition technology based on convolutional neural networks and adaptive learning mechanisms, can enable real-time monitoring, risk prediction, and early warning for vulnerable areas like the middle wall, while optimizing blasting parameters to enhance construction efficiency and safety. This study provides valuable insights and references for improving the construction stability and intelligent development of double-arch tunnels without middle drift.
  • Study on Vibration Propagation Characteristics of Dynamic Compaction of Adjacent Reinforced Soil Slope
    Ma Yaoyu, Xie Qiang, Xue Xiaoqiang, Xu Yongping, Bai Fusheng
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1909-1918. https://doi.org/10.20174/j.JUSE.2026.05.33
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    With the advancement of major infrastructure construction in complex mountainous areas in the central and western regions, the coordinated construction of dynamic compaction and fill slope support has become a key challenge. Although the dynamic compaction method can effectively reinforce the foundation, the vibration wave caused by the impact load can easily lead to the instability of the reinforced soil slope. Based on the high fill project of a converter station in southwest China, this paper studies the vibration propagation characteristics of dynamic compaction of adjacent reinforced soil slope through field detection, FFT filtering processing and discrete element numerical simulation. The effective vibration signal is extracted by FFT low-pass filtering (cut-off frequency 40 Hz), and the discrete element model of reinforced soil slope is established based on PFC3D, which is compared with the field test results. The results show that: The peak value of dynamic compaction vibration velocity decays in a negative power function with the tamping distance, and the attenuation coefficient in the grille area is significantly higher than that in the non-grille area, indicating that the reinforced soil area after geogrid treatment can enhance the vibration attenuation. The peak vibration velocity of the slope decreases linearly along the 45° slope, and the maximum vibration velocity decreases to 0.05~0.09 m/s after optimization. The research reveals the regulation mechanism of grid reinforcement on the vibration propagation path, which can reduce the plastic deformation risk of the adjacent reinforced soil slope by adjusting the tamping energy level and the tamping distance. It provides a certain reference value for the coordinated construction of dynamic compaction and support, foundation treatment and slope stability control under complex terrain.
  • Research on Leakage Mechanisms and Performance of Different Waterproofing Systems for Shield Tunnel Joints
    Li Tengfei, Zhang Gaole, Zhang Wenjun, Yang Yang, Yu Yong
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1919-1928. https://doi.org/10.20174/j.JUSE.2026.05.34
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    To clarify the performance evolution laws and failure modes of different waterproof systems for shield tunnel segmental joints, a research method combining numerical simulation and indoor testing was adopted to comparatively study three typical waterproof systems: single sealing gasket, double sealing gasket, and double sealing gasket considering bolt holes. Based on the Coupled Lagrangian-Eulerian (CEL) method, fluid-solid coupling models of the three waterproofing systems were established, revealing the leakage failure mechanisms of different waterproofing systems. Using a self-designed multifunctional waterproof performance testing device, waterproof performance tests were conducted on the different waterproofing systems, verifying the reliability of the numerical simulations, and further comparing and analyzing the waterproof performance of the three systems under different joint deformations. The research results indicate that the structural configuration of different segmental joint waterproofing systems dominates the evolution of their failure modes, exhibiting “single-point brittle” failure (single-gasket system), “series toughness enhancement” (double-gasket system), and “bypass short-plate” failure (double-gasket system considering bolt holes), respectively. In addition, both the opening and offset deformation of segmental joints can lead to the deterioration of the waterproof performance of different systems, and the double-gasket system is more sensitive to offset. The overall waterproof capacity of the double-gasket waterproofing system follows the “systematic barrel theory”, and its performance is significantly limited by weak links such as bolt holes. The revealed “bypass short-plate” failure mode and “systematic barrel theory” establish a new “performance matching” principle for the optimization design of double-gasket waterproofing systems for segmental joints in high-pressure tunnels.
  • Risk Classification Boundaries for Shield Cutterhead Clogging in Heterogeneous Soft-Hard Stratum
    Deng Shengjun, Zheng Xiufu, Lin Huanyu, Li Lin, Bai Yun
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1929-1937. https://doi.org/10.20174/j.JUSE.2026.05.35
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    During shield tunneling in heterogeneous soft-hard strata, cutterhead clogging frequently causes project delays, while conventional risk classification systems exhibit evaluation deviations due to the lack of stratum-specific risk classification boundaries. This study proposes a risk classification boundary determination method for cutterhead clogging based on liquid-plastic limit indices. A modified rotary stirring adhesion test apparatus was employed to systematically investigate six proportioning schemes of montmorillonite-kaolinite composite clay and sand, revealing the clay-metal interface adhesion mechanism under varying water contents (5% to 100%). By integrating dual-parameter indices of adhesion rate (λ) and coverage rate (S), the adhesion behavior at the clay-metal interface has been successfully characterized. An analysis was conducted on the correlation between the soil's liquid-plasticity index(IL,IP) and both the adhesion rate (λ) and coverage rate (S), and quantitative threshold determination was applied to formulate grading criteria. Key findings include:(1) The adhesion rate of soil samples shows a single peak distribution with the increase of liquid index, and the peak value appears in the range of 0.25~0.65. The peak adhesion rate of high montmorillonite mixed soil with plasticity index > 28 (clay content ≥70%) reaches 0.325; (2) The coverage rate demonstrates a positive correlation with water content, surpassing 80% for high-montmorillonite soils (plasticity index > 31.1) when the liquidity index exceeds 0.25; (3) The revised classification standard identifies three distinct risk zones: High-risk zone: liquidity index between 0.25 and 0.65 combined with plasticity index>28; Medium-risk zone: liquidity index from 0.0 to 0.25 or 0.65 to 1.0, paired with plasticity index between 15 and 28; Low-risk zone: liquidity index from -0.25 to 0.0 or 1.0 to 1.5, accompanied by plasticity index between 10 and 15. The risk classification for clogging risk stratification of shield cutterhead provides quantitative guidance for geology-specific risk prevention.
  • Simulation Technique of Landslide Disaster in Mountainous Regions Based on Coupled GIS-MPM
    Sun Fan, Fan Zeying, Yu Hao, Gong Sheng, Cao Cong
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1938-1947. https://doi.org/10.20174/j.JUSE.2026.05.36
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    Landslide disasters are widespread and severe in China, and they are particularly intense in the mountainous region. The numerical simulation technologies and evaluation techniques utilizing Geographic Information Systems (GIS) have become two pivotal research methodologies within the realm of landslide disaster studies. This paper presents a seamless coupling of Material Point Method (MPM) with the GIS technology, leveraging the simulation capabilities of numerical methods alongside the efficient data management and visualization capacities of GIS. The focus lies on the fundamental theories of large deformation MPM. Concurrently, a landslide simulation method grounded in the seamless coupling of GIS-MPM is introduced. An ArcGIS-based scripting tools and a simulation platform that can run independently from the ArcGIS platform were developed, thus eliminating the need for data transfer across different software platforms, thereby enhancing integration flexibility, operational convenience, and computational efficiency. Ultimately, based on a real case study, the GIS-MPM coupling technique is applied to calculate and analyze the geometric and kinematic characteristics of a landslide throughout its entire process—from instability and failure to sliding accumulation. Furthermore, we achieve three-dimensional visualization using ArcGIS, significantly elevating the level of information and intelligence in mountain landslide disaster research.
  • Research on Safety Threshold of Flood Defense in Rail Transit
    Lu Xian, Chen Feng
    Chinese Journal of Underground Space and Engineering. 2026, 22(5): 1948-1954. https://doi.org/10.20174/j.JUSE.2026.05.37
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    In the context of global climate change, urban rail transit systems are facing increasingly severe flood risks, but existing defense standards lack scientific basis and their applicability is controversial. This study systematically analyzes the similarities and differences between rail transit and urban flood prevention, constructs a three-level defense system including basic defense, over limit defense, and emergency defense, and proposes corresponding threshold determination methods. Taking Shanghai as an example, based on the spatial distribution characteristics of 1091 (82%) ground entrances and exits located in the strong drainage system, passive inundation simulation were used, combined with probability statistical methods, to establish a graded defense threshold: (1) the basic defense threshold is determined based on the elevation of the 100 year flood water accumulation and the surrounding ground elevation; (2) The defense threshold for exceeding the standard adopts the safety ultra-high value with a 95% guarantee rate; (3) The emergency defense threshold simulates the dynamic response of flood control system failure scenarios through a dam breach model. The research results indicate that the current fixed water blocking height standard is difficult to adapt to complex terrain conditions, while the three-level defense system can significantly improve the system's disaster resilience through layered defense. This study provides a scientific quantitative decision-making tool for flood prevention in mega city rail transit, which has important theoretical value and practical significance for improving the resilience design standards of urban infrastructure.
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