A finite strain solution incorporating 3D stresses and steady-state seepage for circular tunnels in strain-softening rock

Effects of surrounding rock surface morphology in hard rock tunnels on adhesion strength and failure characteristics of fiber-reinforced shotcrete-rock interfaces

Design and laboratory-based proof-of-concept verification of electromagnetic energy harvesting device for multi-state monitoring of large-diameter TBM gauge cutters

Large deformation in soft rock tunnels remains a critical challenge in mining and underground engineering, with conventional rigid supports prone to overstressing and failure due to limited deformation compatibility. Although yielding supports with resistance limiters such as inflatable airbags and circular steel bellows (CSBs) provide improved adaptability, current design approaches remain largely empirical or overly simplified. As a result, they lack a unified constitutive framework that can quantitatively describe their multi-stage mechanical behavior and effectively link it to performance-based design. To address this gap, this study develops and experimentally validates a novel constitutive model that characterizes yielding supports through three explicit phases: elastic yielding (initial stiffness ko = 0.18-0.25 kN/mm), post-yield hardening (hardening stiffness kh = 0.42-0.68 kN/mm), and locking (ultimate resistance FL = 2.0-2.4 kN). To enable quantitative performance assessment, eight dimensionless indices are introduced, including the yielding ductility ratio (μ), deformation capacity envelope (Ω), plasticity index (ψ), strain localization index (LƐ), strain uniformity index (UƐ), support adaptability index (SAI), and energy-reaction coupling coefficient (η). Large-scale model tests demonstrate that airbag limiters reduce vertical deformation by approximately 35% relative to rigid supports and exhibit superior early-stage adaptability (Ω ≈ 0.46), whereas CSBs provide higher energy dissipation (Ed = 50-55J), greater strain uniformity (Uε ≈ 0.79), and enhanced stability through post-yield hardening. The proposed framework further integrates these indices into practical design tools, including stability maps based on stiffness ratios (α = ko/kr, β = kh/kr) and the Yield-Hardening Design Surface (YHDS), enabling performance-based selection and optimization of yielding supports under squeezing conditions. This work provides a validated, mechanics-based, and metrics-driven approach to mining and tunnel support design, effectively bridging the gap between constitutive modeling and practical engineering application.

ABSTRACT Rock bursts pose a significant challenge in deep hard rock tunnel engineering. This study investigates the energy evolution during rock failure through uniaxial upper-limit loading and unloading tests, establishing a connection between rock energy storage characteristics and rock burst tendency. True triaxial loading tests on tunnel models are employed to analyse the relationship between stress paths, rock stress magnitude, and rock bursts. By integrating the rock’s energy storage properties and the stress conditions within the rock mass, a new evaluation index, Stress and Energy Storage Density (SESD), is proposed to assess the rock burst tendency. A case study on rock burst during double-shield TBM excavation reveals that the disaster incubation process progresses in six stages: elastic state, crack initiation, crack propagation, fragment ejection, slab fracture buckling, and unstable failure. The SESD index incorporates both rock strength and energy dynamics, capturing the stress state during excavation and the associated energy accumulation-release process in surrounding rock. Numerical results show that SESD variations closely match actual rock burst occurrences, validating their effectiveness in simulation-based analysis. This study introduces a novel energy-stress coupled method for rock burst prediction, offering clear modelling principles, practical applicability, and robust adaptability for complex engineering scenarios.

Under the complex geological conditions of high quartz content, high compressive strength and composite strata, the full-section hard rock tunnel boring machine (TBM) cutter ring is prone to fracture and wear when subjected to a large impact load, which seriously reduces the tunneling efficiency of the TBM and increases the construction cost. In order to solve the above problems, this paper aims to improve the hardness of the cutter ring while taking into account the high toughness of the cutter ring as the goal, based on the DFEORM to establish a gradient hardness cutter ring induction tempering heat treatment finite element simulation model, to study the tempering process parameters of the cutter ring hardness and toughness of the influence of the law, and through the induction tempering experiments on its verification, and ultimately get the edge part of the high hardness and high tenacity of the high performance of the gradient hardness of the cutter ring heart part. The results show that increasing the heating time, current density and current frequency can effectively expand the softening area of the cutter ring to improve the toughness of the cutter ring heart, and increasing the air gap can effectively reduce the softening degree of the cutter ring to improve the hardness of the cutter ring. The optimal combination of the induction tempering parameters is as follows: current density between 5.31A/mm2 and 5.94A/mm2, current frequency between 5kHz and 10kHz, induction tempering time between 6min and 8min, and air gap between 4mm and 8mm.

In viscoelastic-plastic surrounding rock, rheological processes gradually increase support reaction forces, affecting the stress state. Analyzing such rock requires consideration of stress path influences. In high-temperature environments, rock properties change with temperature, further impacting stress paths. Therefore, studying deep buried high geothermal tunnels necessitates analyzing viscoelastic-plastic surrounding rock while accounting for both high-temperature effects and stress paths. The coupling of high-temperature effects and stress paths influences the stress state of tunnel rock. By combining the Mohr-Coulomb strength criterion with the generalized Kelvin rheological model, we optimize stress, strain, and displacement calculations for supported viscoelastic-plastic surrounding rock. We derive analytical solutions for stresses, wall displacements, and plastic zone radii in viscoelastic-plastic surrounding rock, considering strength parameter deterioration due to high-temperature effects and stress paths. Using existing research on granite’s physical and mechanical parameter variations with temperature, we develop temperature-dependent fitting equations for granite's physical parameter deterioration. We theoretically calculate and analyze relationships among surrounding rock stress, tunnel wall displacement, and plastic zone radius. Results indicate that as temperature increases, its impact on rock’s physical properties significantly affects stress and strain. Moreover, as temperature gradually rises, the rock’s physical properties undergo additional changes, amplifying the impact of high-temperature effects.

Instability analysis of circumferential and radial yielding structures in high in-situ stress soft rock tunnels based on polyurethane foam

Physics-data driven approach for multi-objective intelligent prediction and optimization of deep soft rock tunnel stability

Model tests and discrete element simulations on the cracking characteristics of layered soft rock tunnel under different bedding features

Bayesian updating of analytical model to predict time-dependent large deformation in soft rock tunnel

Performance analysis of an integrated excavation-milling-hooking-throwing system for soft rock tunnel excavation

Research on the radial microstructure evolution behavior of DC53/42CrMo composite tube billets produced by centrifugal casting method

Deciphering the time-dependent behavior of underground rock tunnels: Insights from a generalized non-associative thermo-viscoplastic damage model

Time-dependent optimization of support application timing in soft rock tunnels considering creep deformation and structural degradation

A sliding window feature extraction and weight adaptive random forest-based method for TBM tunnel rock mass grade identification

ABSTRACT Rapid and precise estimation of rock mechanical parameters, such as elastic modulus and Poisson’s ratio, is a critical yet unresolved challenge in geotechnical engineering. Traditional laboratory and in situ tests are often slow, expensive, provide only discrete, point-based data, and can suffer from sample disturbance or size effects. In this study, a rock drilling model compliant with the Drucker–Prager (D-P) criterion is first built via finite element simulation. After validation, a hybrid Long Short‑Term Memory (LSTM) and Mixture‑of‑Experts (MoE) neural network is developed to predict the elastic modulus and Poisson’s ratio directly from weight on bit (WOB) and torque time series. Verified through laboratory tests on seven typical sandstone lithologies, this model demonstrates significantly higher prediction accuracy than conventional methods (R2 = 0.9351 for elastic modulus, R2 = 0.9317 for Poisson’s ratio). This approach provides reliable numerical simulation data and is capable of acquiring rock mechanics parameters reliably, continuously, and in real time, meeting the urgent demand for real-time, while-drilling data in engineering practices such as tunnel rock mass classification, slope stability evaluation, and foundation bearing capacity computation.

Currently, the classification of weathered degrees in granite surrounding rock of subsea tunnels primarily relies on preliminary methods such as field characteristic observation, rock sample compressive strength test and wave velocity test. These approaches offer limited accuracy and yield relatively coarse classification results, which can lead to misjudgments regarding rock stability during tunnel design and construction. As a result, weak surrounding rock areas that should have been treated with grouting reinforcement may be overlooked, increasing the risk of tunnel face collapse or water inrush. Based on the weathering characteristics of granite surrounding rock of subsea tunnels with different weathered degrees along the southeastern coast of China, this study aims to provide a more reliable basis for the refined classification of surrounding rock, thereby helping to avoid the occurrence of such engineering accidents. The mechanical properties of weathered granite were evaluated through uniaxial compressive and triaxial compression tests. Then, the polarizing microscopy and the X-ray Computed Tomography (X-ray CT) were employed to obtain the variations in microstructural parameters of weathered granite. Subsequently, X-ray diffraction (XRD) analysis was performed to examine the mineral composition of granite with varying degrees of weathering. The results indicate that weathering not only reduces the mechanical strength of the granite surrounding rock but also increases its porosity. Additionally, the content of clay minerals within the granite surrounding rock continuously increases with the degree of weathering, particularly in completely weathered granite, where clay minerals dominate the composition. This further causes the surrounding rock structure to loosen, increasing the number of pores and ultimately reducing the overall strength and stability of the surrounding rock. Finally, the mathematical relationships between the mechanical parameters, pore fractal dimension, and clay mineral content were established to quantitatively characterize the weathering effect of granite surrounding rock. These results could serve as reference for the construction of subsea tunnels crossing weathered granite strata.

ABSTRACT Based on the complex variable method and the corresponding principle of viscoelasticity, viscoelastic solutions for the stress and displacement of a lined non‐circular tunnel subjected to in‐situ stresses and internal water pressure is derived. The basic equations for solving the analytic functions are established according to the stress boundary condition along the inner boundary of the lining and the stress and displacement continuity conditions along the rock‐lining interface. The analytic functions are expressed as Laurent series and the Laplace transformation is performed on the basic equation. Herein, the power series method is applied to obtain the linear equations which are expressed by the analytic function coefficients in the Laplace domain. The stress and displacement solutions of tunnel in Laplace domain can be addressed by solving the equations, and then the viscoelastic solutions are obtained through Laplace Inverse transformation. Subsequently, an example for the horseshoe‐shaped tunnel is performed. The example used the generalized Kelvin model to simulate the rheological properties of surrounding rock mass. The obtained solution is compared with the numerical solution. The influences of the lateral pressure coefficient and the internal water pressure on the stresses and displacements of lining are analyzed.

During the excavation of the Qinling Water Conveyance Tunnel, rockbursts influenced by structural planes with varying dip angles occurred frequently, posing a significant threat to personnel and construction safety. This study combines statistical analysis of rockburst cases, numerical simulation, and microseismic monitoring to systematically reveal the influence mechanism of structural plane dip angle on rockbursts. Statistical results indicate that intense rockbursts occurring in the dip angle interval of 0–30° account for 60%. Numerical simulations further demonstrate that dip angles of less than 90° (especially near 10°) induce continuous stress accumulation, leading to large-scale instability. Specifically, the peak acoustic emission (AE) count at a dip angle of 10° is significantly higher than in other configurations, further indicating the highest rockburst risk. Incorporating the influence mechanism of structural plane dip angle into microseismic monitoring analysis significantly improved prediction accuracy. This approach successfully predicted an intense rockburst. Based on these findings, engineering suggestions regarding excavation direction and rockburst early warning optimization are proposed, offering a valuable reference for rockburst mitigation in deep-buried tunnels under similar geological conditions.