In karst tunnel engineering, water-filled cavities located above the tunnel crown, under the combined effects of excavation disturbance and hydraulic pressure, are prone to triggering water and mud inrush disasters. The thickness of the water-resisting rock layer is therefore a key factor controlling the stability of the surrounding rock. To address the difficulty in accurately characterizing the mechanical behavior of the crown of horseshoe-shaped tunnels using conventional circular plate or beam models, this study innovatively develops an explicit analytical model for the minimum safe thickness of the water-resisting rock layer based on clamped elliptical thin plate theory and Kirchhoff plate theory, incorporating the influence of cross-sectional geometry. Parametric sensitivity analysis indicates that both karst water pressure and tunnel crown height significantly amplify the required minimum safe thickness, whereas an increase in the tensile strength of the surrounding rock effectively reduces the thickness demand. Specifically, when the karst water pressure increases from 2.5 MPa to 4.5 MPa, the minimum safe thickness rises from 7.5 m to 10.0 m, showing an approximately linear growth trend. The analytical model is further validated through numerical simulations under different “water pressure–thickness” conditions. The results demonstrate that at the calculated recommended thickness, the surrounding rock achieves stable convergence after excavation. High tensile stress and elevated pore pressure zones are mainly concentrated near the tunnel crown, without the formation of through-going tensile failure. Engineering application indicates that the proposed model can provide a quantitative basis for the design of water-resisting rock layer thickness and the assessment of water inrush risk in karst tunnels.

Response characteristics and influence mechanism of lining structures under dual-indices blockage of longitudinal drainage pipe in karst tunnels

A multi-scale analysis of karst tunnel collapse induced ground subsidence based on continuous-discrete coupling method

Rockfall seriously threatens the construction and operation safety of karst tunnel. Obtaining the damage characteristics of tunnels under rockfall impacts is of great significance to optimize the design of protective structures, but is still unclear. In this study, a bond-based peridynamic (BBPD) method taking the strain rate influence of failure criterion into account is proposed. The accuracy and effectiveness of the proposed BBPD method was verified by comparing it with two experimental tests. Further numerical analyses using the proposed BBPD method were conducted to identify the influence of factors, including the impact velocity and impact position, on the damage characteristics of protection measures of a karst tunnel under rockfall impact. Protection measures include the composite lining, the composite lining with reinforced arch, and the composite lining with reinforced arch and buffer layer. The results show that the structural damage index follows a three-stage growth rule, including rapid growth period, slow growth period, and gradual stability period. The impact velocity and position have a significant effect on the structural damage index. The higher the impact velocity and the closer the impact position to the structural vault area, the greater the structural damage index. Under the three protection conditions, the tunnel damage index basically meets the requirements from large to small: the composite lining > the composite lining with reinforced arch > the composite lining with reinforced arch and buffer layer. The advantage for damage index reduction is not obvious for polyurethane thicknesses over 2.5 m. Finally, a composite lining with reinforced arch and buffer layer is proposed, which can resist the impact of the rockfall with a mass of 7.5 t falling freely from 105 m.

This paper investigated the mechanism and dynamic process of a significant water and mud inrush disaster that occurred in the Baiyunshan Tunnel, which crosses a karst fault zone. By integrating multi-source data including geological exploration and geophysical surveys, a three-dimensional geological model characterizing the cave–conduit–tunnel system was developed. A numerical approach coupling the Phase-Field and Particle-Tracking Methods was employed, successfully reconstructing the entire disaster process involving the transport of water-air-mud three-phase flow. Simulation results demonstrated that the dynamic viscosity of the mudflow predominantly controls the dynamic characteristics of the particle, such as transport distance and mudflow velocity. Parameter sensitivity analysis revealed quantitative relationships between key mudflow parameters (transport distance, velocity, and drag force) and the Reynolds number, identifying an exponential decay of drag force with increasing Reynolds number in high-viscosity mudflows. This study establishes a comprehensive methodology from geological identification to numerical simulation, providing a theoretical basis and technical support for precise risk assessment and the design of preventive measures for tunnel water and mud inrush disasters.

Water inrush risk assessment during karst tunnel construction based on knowledge decision and data-driven methods

Soluble rocks such as limestone and dolomite can form karst features, including caves, sinkholes, and solution grooves through prolonged groundwater erosion (Parise et al., 2015). Karst landscapes are widespread globally. Construction in karst areas often faces sudden and severe ground collapse risks, endangering project safety, structural integrity, and personnel well-being. Therefore, the detection, assessment, and treatment of karst formations are crucial in engineering.Geotechnical investigation in karst regions necessarily includes karst detection. Current methods are diverse, primarily comprising geological mapping, engineering drilling, and geophysical exploration (Li and Xiao, 2006;Goldscheider et al., 2011;Kaufmann, 2014). Among these, geophysical techniques impose relatively fewer constraints and are more widely applied. Wang et al. (2025a) detailed the principles and data processing methods of four geophysical exploration approaches for karst detection: multi-electrode resistivity, cross-hole electromagnetic wave computed tomography, microtremor survey, and ground-penetrating radar.They compared the applicability of each method through case studies. A novel one-shaped layout 3D electrical exploration model has been proposed for detecting karst groundwater channels, improving exploration efficiency by 85.9% over conventional methods while maintaining high accuracy (Wang et al., 2025b).Karst collapse, a common hazard in such regions, is characterized by strong concealment, abrupt occurrence, and high destructiveness, capable of causing sudden surface subsidence and damage to structures. Thus, assessing and predicting karst collapse is essential.Machine learning has been a transformative tool in addressing various science and technology problems (Qu et al. 2021, Qu et al. 2023) .For example, it has been used for predicting potential hazards in tunnel engineering (Zhang et al., 2025;Qu et al., 2025;Yuan et al., 2026). To address the need for high-precision karst collapse assessment, Wang et al. The mechanism of dynamic grouting with self-expanding slurry for water plugging in karst tunnels was examined by Zhan et al. (2025). Tang et al. (2025) revealed that karst water erosion causes grouting curtain leakage mainly due to severe degradation of cement-clay composites, which are less durable than pure cement grouts. The pressure filtration effect in karst areas significantly enhances the initial consolidation strength of grouted curtains, necessitating a revised life prediction model that incorporates this effect for accurate service life forecasting, as validated through experiments and field application (Yan et al., 2025). Yao et al. (2025) demonstrated that integrating high-density resistivity and frequency-division electrical resistivity tomography with geological methods provides an accurate, practical, and broadly applicable approach for diagnosing leakage risks in karst reservoir dams.Shield tunneling through karst strata poses risks such as shield machine sinking, head pitching, ground settlement or collapse, and excessive postconstruction settlement (Cheng et al., 2017), which can cause serious hazards, significant economic loss, and even casualties (Xie et al., 2025;Ou et al., 2025b).Based on a shield tunneling project in Shenzhen, China, Li et al. (2025) proposed a membrane-sleeve valve pipe grouting technique for reinforcing karst strata, building on conventional sleeve valve pipe grouting. They detailed its key construction points and process, with field tests confirming its applicability. A combined short straight-hole and wedge compound cut blasting scheme was proposed and tested in a hard rock tunnel (Tu et al., 2025). Various machine learning techniques have been leveraged to integrate geological records and tunneling parameters for predicting rock grades (Dang et al., 2025). Mechanistic analysis of TBM cutterhead-ground interaction under the mud build-up effect was explored by Wang et al. (2025d).Finally, we extend our gratitude to everyone who contributed to this special issue. Their contributions include not only theoretical breakthroughs but also the accumulation and sharing of practical engineering experience. Through their dedicated efforts, challenges in karst construction are being progressively overcome, providing valuable references and insights for similar projects.PL: Conceptualization, Writing-original draft. PC: Investigation, Writing review and editing. XS: Writing-review and editing. XF: Writingreview and editing. CZ: Writing-original draft.

Based on the theory of fluid structure coupling, taking the karst tunnel in Zhongliangshan, Chongqing, as the research object, the numerical simulation method is used to study the spatiotemporal movement law of groundwater during the construction period and its impact on the stability of the tunnel. By comparing the differences in seepage field, displacement field, stress field, and water inflow between the three-step method and the double-sided wall guide method, the influence of the initial water head height and the surrounding rock’s permeability coefficient on the construction process was analyzed. The research results indicate that the double-sided wall guide method significantly reduces the deformation of the surrounding rock through the temporary support system (reducing the arch crown settlement by 48.78% and the arch bottom uplift by 31.13%), making it more suitable for construction in high water pressure and rich water formations. The permeability coefficient and head height have a significant positive impact on water inflow. The research results provide a theoretical basis and technical support for the selection of construction methods and disaster prevention in tunnel construction under complex hydrogeological conditions.

The stability of rock masses in karst regions is critically influenced by the coexistence of karst caves and joints. This study investigates the mechanical behavior, energy evolution, and failure modes of large-scale (1 m3) rock-like specimens containing a 30 cm karst cave and joints at varying positions and dip angles (α). The results indicate that joint dip angles between 30° and 60° define a critical strength deterioration zone, with the minimum peak strength (44 MPa, 24.1% lower than the 0° specimen) occurring at α = 60°. Side-positioned joints induced greater strength weakening than top-positioned ones. Energy analysis revealed that α significantly governs energy accumulation and dissipation; the elastic energy minimum was also observed at α = 60°. Specimens with side-positioned joints exhibited higher energy dissipation efficiency, promoting extensive crack propagation. The research results suggest that in engineering, are as with joints inclined at 30–60° should be avoided as much as possible, and the energy-dissipating capacity of near-vertical (~90°) joints should be utilized to enhance the stability of the rock mass in karst tunnel engineering.

Seepage instability mechanism of water inrush channel in non-uniform filling-type karst tunnels under different fine particle contents

Investigation of the minimum safe thickness of water-resistant strata in vertically layered karst tunnels considering seismic action

Face stability of karst tunnels considering drag force of connected fracture based on limit analysis

Tunnel construction in karst formations faces significant geological uncertainties, which pose challenges for quantifying construction risks using traditional deterministic methods. This paper proposes a probabilistic reliability analysis framework that integrates the Stochastic Finite Element Method (SFEM), a Radial Basis Function Neural Network (RBFNN) surrogate model, and Monte Carlo Simulation (MCS) method. The probability distributions of rock mass mechanical parameters and karst geometric parameters were established based on field investigation and geophysical prospecting data. The accuracy of the finite element model was verified through existing physical model tests, with the lateral karst condition identified as the most unfavorable scenario. Limit state functions with control indices, including tunnel crown settlement, invert uplift, ground surface settlement and convergence, were defined. A high-precision surrogate model was constructed using RBFNN (average R2 > 0.98), and the failure probabilities of displacement indices were quantitatively evaluated via MCS (10,000 samples). Results demonstrate that the overall failure probability of tunnel construction is 3.31%, with the highest failure probability observed for crown settlement (3.26%). Sensitivity analysis indicates that the elastic modulus of the disturbed rock mass and the clear distance between the karst cavity and the tunnel are the key parameters influencing deformation. This study provides a probabilistic risk assessment tool and a quantitative decision-making basis for tunnel construction in karst areas.

Mechanical Characterization and Deterioration Mechanism of Karst Tunnel Limestone under Hydrochemistry and Three-Dimensional Stress

Frequent water and mud inrush accidents during karst tunnel construction severely impact tunnel construction safety, environmental sustainability, and the long-term use of infrastructure. Therefore, conducting practical risk assessment for karst tunnel water and mud inrush is crucial for promoting sustainable practices in tunnel engineering, as it can mitigate catastrophic events that lead to resource waste, ecological damage, and economic loss. This paper establishes an improved weighted cloud model for karst tunnel water and mud inrush risk to evaluate the associated risk factors. The calculation of subjective weight for risk metrics adopts the ordinal relationship method (G1 method), which is a subjective weighting method improved from the analytic hierarchy process. The calculation of objective weight employs the improved entropy weight method, which is superior to the traditional entropy weight method by effectively preventing calculation distortion. Game theory is applied to calculate the optimal weight combination coefficient for two computational methods, and cloud model theory is finally introduced to reduce the fuzziness of the membership interval during the assessment process. This study applied the established risk assessment model to five sections of the Furong Tunnel and Cushishan Tunnel in Southwest China. The final risk ratings for these sections were determined as “High Risk,” “High Risk,” “Medium Risk,” “High Risk,” and “Moderate Risk”, respectively. These results align with the findings from field investigations, validating the effectiveness and reliability of the cloud model-based mud and water outburst risk assessment using combined weighting. Compared to traditional methods such as fuzzy comprehensive evaluation and entropy weighting, the evaluation results from this study’s model demonstrate higher similarity and reliability. This provides a foundation for assessing mud and water outburst hazards and other tunnel disasters.

Clarifying the mechanism of grouting to block karst water outbursts is essential for ensuring effective sealing. This article studies the grouting blocking problem related to the prevention and control of water surge disasters in karst tunnels, focusing on the grouting blocking mechanism of efficiently plugs expanding material (EPEM) under dynamic water conditions. We propose a grouting diffusion formula and blocking criterion that take into account the self-expanding properties of the slurry. First, based on the equilibrium relationship between the friction force and anti-splitting force between the blocking body and the rock wall, we establish an effective blocking condition. Second, by combining capillary theory with Newton’s fluid constitutive equation, we derive the diffusion distance formula for self-expanding slurry under dynamic water conditions. We then construct a mechanical model that uses the length of the critical blocking body as a criterion, revealing the coupling influences of groundwater pressure, grouting pressure, and grouting time. The results indicate that groundwater pressure is positively correlated with grouting pressure and grouting time, while grouting pressure is negatively correlated with grouting time. Finally, we verify the practicality of the proposed criterion through the project at Quanmutang Reservoir in Hunan Province, successfully implementing a parameter combination of 0.5 MPa grouting pressure and 20 min of grouting time to block surge water. This research provides a theoretical basis and engineering guidance for designing water surge grouting in karst tunnels.

Theoretical and numerical study of the failure mechanism and minimum safety thickness of water-resistant rock mass in layered karst tunnels

Karst tunnels accumulate localized high water pressure during heavy rainfall, which can potentially induce cracks and damage to tunnel structures. By fully analyzing the stress characteristics of the lining structure and the critical water pressure, this study aims to evaluate the safety status of karst tunnels under heavy rainfall conditions, and proposes detailed tunnel optimization solutions. The results indicate that the outward deformation of the structure is restricted when the water pressure within the cavity is low, thus enhancing structural stability. However, the internal forces of the structure gradually increase as water pressure increases. Additionally, the mechanical properties of the surrounding rock significantly influence the internal forces. The bending moment in the lining structure is highest in the grade III surrounding rock under the same water pressure. However, the critical water pressure of the lining structure differs by surrounding rock grade due to varying constraints, following the order IV > V > III. Moreover, karst cavities located at the arch spandrel exert the greatest detrimental effect on the structure. Furthermore, the critical water pressure and concrete failure modes of the lining structure under different conditions are determined. Lastly, the optimization of the construction and design of the actual tunnel is proposed to enhance the structural integrity of the tunnel lining. These findings provide valuable insights for structural safety assessments under various karst cavity conditions.

[Objective] This study aims to assess and predict the risks of water inrush and leakage during tunnel excavation in karst regions, where groundwater intrusion poses serious threats to construction safety and long-term hydrogeological sustainability. [Study area] This study is conducted in the Qigan Mountain, involving detailed hydrogeological surveys and hydrochemical analyses to understand the subsurface conditions. [Methods] Numerical simulation methods are employed to model the regional seepage field distribution under natural conditions and two excavation conditions, using MODFLOW. [Challenges] One of the main challenges is accurately estimating tunnel water inflow under varying geological and hydrological conditions. [Results] The simulation results indicate that under excavation with blocking conditions, tunnel water inflow reaches 31,932 m3/d, whereas without blocking, inflow surges to 359,199 m3/d. In contrast, the theoretical calculation estimates a water inflow of 131,445 m3/d, revealing considerable discrepancies between the methods. [Recommendations] These findings highlight an important point of reference for the prevention of water influx in karst tunnel construction.

The design of waterproofing and drainage is crucial in tunnel construction within high-pressure water-rich karst regions. Improper groundwater treatment can damage the ecology and compromise tunnel structural safety. Currently, the fully drained or fully waterproofed strategies are widely used in high-pressure, water-rich karst tunnels. However, these methods either disrupt the balance of water resources or cause the lining to bear full head pressure. Thus, this study proposes the principle of mainly waterproofed with limited drained strategy. Using the deep-buried water-rich mountain tunnel as a case study, the three aforementioned drainage designs were implemented. Through numerical analysis of FLAC3D, the distribution rules of seepage, displacement and stress field of the lining structure under different drainage conditions are obtained. Results indicate that mainly waterproofed with limited drained strategy maximizes groundwater resource protection, enhances surrounding rock waterproofing, and distributes water pressure on the lining structure. Additionally, it was found that the permeability coefficient and thickness of the grouting ring influence the water blocking and reinforcement effects. Finally, during the Dejiang Tunnel construction, implementing mainly waterproofed with limited drained strategy altered the lining’s water pressure values. This paper can provide a reference for the design, construction and remediation measures of high-pressure water-rich karst tunnels.