Deep Tunnel Research Articles

Design of deep rock tunnels using hyperstatic reaction and convergence confinement methods

Tunnel lining is usually installed with delay behind the tunnel face excavation, which requires that a displacement is considered at the tunnel boundary before the support structure installation. This delayed installation comes with a release and redistribution of stress in the rock mass. Internal tunnel lining forces significantly rely on the stress relaxation process taking place in the rock mass surrounding the excavated tunnel. One of the difficulties when designing tunnel supports is, therefore, to analyse the rock–support interaction considering the tunnel lining convergence caused by the stress redistribution. Here, a simple and effective calculation process based on the combination of two methods, the hyperstatic reaction method (HRM) and convergence confinement method, is presented to analyse the interaction of rock mass and support structure. The rock mass is assumed to obey the Hoek–Brown criterion. The stress release is also taken into consideration. The present method is validated by comparing results of the HRM in terms of tunnel lining forces against the analytical ones. Thereafter, the effect of the stress release coefficient, the tunnel depth and the Hoek–Brown criterion parameters (the geological strength index and σci) on the lining internal forces are presented and discussed.

Three-dimensional stress rotation and control mechanism of deep tunneling incorporating generalized Zhang–Zhu strength-based forward analysis

Deep rock tunneling exhibits a significant three-dimensional (3D) space effect. The complex stress path and extrusion deformation during excavation are the most significant and decisive factors in the stability and construction safety of a deep tunnel. 3D and forward numerical analyses based on generalized Zhang–Zhu (GZZ) strength criterion are performed to investigate the principal stress rotation behavior and active control mechanism during deep tunneling. The surrounding rock element experiences significant stress rotations because of the sharply increased shear stress (τry) near the tunnel face. A dimensionless stress index (τry/I1) is proposed to quantitatively evaluate the principal stress rotation during excavation. τry/I1 increases with increasing buried depth, and the deep tunnel presents significant principal stress rotation that reaches a large τry/I1 value. The mechanical behavior of the advanced core rock is primarily affected by the strengthening parameter, geological strength index (GSI). Strengthening of the core rock can greatly improve the stress conditions and mechanical behavior, increase the strength of the rock mass, and reduce the stress rotation. The pre-extrusion deformation of the core rock and pre-convergence of the surrounding rock are discovered to follow a consistency law, which suggests that the pre-convergence deformation and surrounding rock stability near the tunnel face depend on the extrusion deformation of the tunnel face. The GZZ strength-based 3D forward analysis and stress control method proposed in this study can enhance the design and construction of deep and ultra-deep tunnels by weakening the 3D space effect (e.g., tunnel face extrusion and stress rotation) and exerting the strength potential (self-bearing capacity) of a rock mass.

Time-variant reliability analysis of underground structures against delayed failure based on the probability density evolution method

The unpredictable delayed failure of underground tunnels may occur after excavation due to the time-dependent behavior of surrounding rock mass, which brings a new consideration to the reliability evaluation of underground structures. In this study, a time-variant reliability analysis procedure via the probability density evolution method (PDEM) is proposed for underground tunnels against delayed failure. The creep-damage theory is introduced to model the time-dependent behavior of rock materials. A new energy-based stability criterion is developed to identify the structural delayed failure. By applying the PDEM with the absorbing boundary condition, the time-varying reliability of underground structures can be obtained. The proposed procedure is applied to a case study involving the deep tunnel with uncertain material parameters. Numerical results demonstrate that the inherent variability of rock properties could result in the large fluctuation of structural delayed responses, which has a significant influence on the time-varying reliability of the tunnels.

Multi-level voxel representations for digital twin models of tunnel geological environment

• An efficient linear segmentation-based multi-level voxel representation method is proposed, aiming to represent the geological environment of the long and deep tunnel. Based on the results of the comparative experiment, the spatial efficiency was augmented by 30% approximately by using this technique. • VDB data structure is used to meet the dynamic update requirement of the digital twin applications. It has the consistent time complexity of random access and uses a narrow-band level set to reduce space complexity. • Multi-source data is integrated to represent the multi-feature geological environment. Four typical data with different modalities (parametric BIM model, B-rep solid model, triangle mesh model, 3D regular grid model) are successfully integrated into the digital twin model. Intelligent tunnel engineering requires accurate and comprehensive digital twin models to represent complex geological environments. The digital twin model of tunnel geological environment has multi-level and diversified in-depth applications such as problem diagnosis, risk assessment, trend prediction, emergency response, etc. Since tunnel construction is a long-term continuous dynamic spatial–temporal progress, the tunnel face constantly advances during excavations. Thus, the geological conditions of the construction surface and surrounding areas are continuously revealed and updated, which causes the digital twin model to have a very high update frequency of the geological information in tunnel engineering. The existing methods fail to represent and update the geological environment comprehensively and in real-time, especially for those long deep tunnels with the complicated topology of geological structures and the heterogeneous distribution of internal properties. Due to the digital twin application having a high-level requirement of completeness, accuracy, and timeliness, 3D modeling of tunnel geological environments has remained challenging within digital twin application contexts. This study aims to deliver a solution that efficiently represents and updates the geological structures and internal non-uniform properties of tunnel engineering. Since dense voxels can represent inner intricate heterogeneous property information, sparse voxels can efficiently represent complex structural information. Meanwhile, voxels using Volumetric Dynamic B + trees (VDB) data structure are easy to integrate and update. However, according to the characteristics of long strip distribution of tunnel geological environments, directly using the VDB will still cause an efficiency problem. Therefore, this study proposes an efficient linear segmentation-based multi-level voxel representation method for the prolonged deep tunnel geological environment using the VDB data structure to support dynamic updates. The typical Mountain Tunnel of China is employed for experimental analysis to validate the proposed method, and four representative data with different modalities are integrated into the digital twin model. The results demonstrate that spatial efficiency augments 28.49% after segmentation, and data access with O(1) time complexity supports efficiently dynamic updates.

Rockburst tendency prediction based on an integrating method of combination weighting and matter-element extension theory: A case study in the Bayu Tunnel of the Sichuan-Tibet Railway

The Bayu Tunnel is the most problematic tunnel project in the Lhasa-Nyingchi section of the Sichuan-Tibet Railway. Rockbursts have occurred frequently during the construction process, which has seriously threatened the safety of construction workers and equipment. Aiming at the rockburst hazard prediction problem of the Bayu Tunnel, in this paper an integrating method of combination weighting and matter-element extension theory is proposed. This method introduces the rock brittleness evaluation index BICSS, Russenes criterion and rock mass integrity coefficient as the main rockburst evaluation indexes, which characterized the control factors of rock physical and mechanical property, surrounding rock stress and rock mass integrity on rockburst tendency, respectively. Then the rockburst tendency evaluation index system is constructed. The weight of each rockburst control factor is determined by the combination weighting algorithm of triangular fuzzy number analytic hierarchy process (TFN-AHP), criteria importance though intercriteria correlation (CRITIC), and determination of comprehensive weight (MDI). The correlation degree between the rockburst sample and rockburst grade can be calculated using the matter-element extension theory, after which the prediction of rockburst grade is carried out. Finally, the applicability, superiority and the necessity of selected rockburst control factors in this method are verified and discussed further. The research results provide a new analysis method and technical means for rockburst tendency assessment of deep tunnel.

Analytical solutions for deep tunnels in strain-softening rocks modeled by different elastic strain definitions with the unified strength theory

Analytical solutions for deep tunnels in strain-softening rocks modeled by different elastic strain definitions with the unified strength theory

Elastoplastic semi-analytical investigation on a deep circular tunnel incorporating generalized Zhang–Zhu rock mass strength

The semi-analytical method based on finite difference method is widely used in the study of the mechanical response of surrounding rocks in a circular tunnel. The core of the three-dimensional (3D) mechanical analysis of the plastic zone is to solve nonlinear equations with a complex yield criterion, which leads to a long iterative solution time and low accuracy. In this study, a new 3D semi-analytical method is proposed for a circular tunnel excavation. The method is based on the finite difference method, wherein a linear equation is used to replace the complex yield surface equation. This significantly reduces the iterative solution process and effectively improves the calculation rate. The accuracy of the proposed method is verified using conventional and 3D numerical methods. The two-dimensional (2D) generalized Hoek–Brown criterion (GHB), 3D generalized Pan–Hudson criterion (GPH), and 3D generalized Zhang–Zhu criterion (GZZ) are used to analyze the applicability of the proposed method. The mechanical properties of a circular tunnel excavation are studied using these criteria. Our results show that the calculation rate of the plastic zone response of the proposed method (based on the GZZ criterion) is 12,000 times higher than that of the conventional iterative method. The overall calculation rate is increased by a factor of 65, and the calculation error is smaller than that of the conventional method. The GHB does not consider the intermediate principal stress, and the GPH cannot reflect the mechanical properties of rock masses with different tensile and compressive strengths, although it considers the intermediate principal stress. The convergence–constraint characteristics of the surrounding rock of the GHB and GPH are significantly different from those of the GZZ. There is an optimal initial axial stress value qopt that yields the smallest deformation of the surrounding rock and the best stability. The internal support pressure and residual strength of the rock mass have a significant effect on the mechanical response of the surrounding rock. The proposed method has acceptable applicability to elastic–brittle and elastic–perfectly plastic rock masses. Additionally, it can be used in the study of deep-buried tunnel excavation at high geo-stresses.

Progressive fracture and swelling of anisotropic rock masses around deep tunnels: a new floor heave mechanical mechanism

Progressive fracture and swelling of anisotropic rock masses around deep tunnels: a new floor heave mechanical mechanism

Analysis of Surrounding Rock Pressure of Deep Buried Tunnel considering the Influence of Seepage

This paper takes the surrounding rock of deep tunnel as the research object and considers the action mechanism under the influence of seepage. Based on the Mohr-Coulomb criterion, the stress mechanism of surrounding rock of deep buried tunnel is analyzed by a convergence constraint method. Based on the elastic-plastic solution, the nonlinear elastic-plastic solution of the interaction between surrounding rock and lining structure considering the effect of seepage force is proposed, and the radius of surrounding rock plastic zone is obtained. The relationship between surrounding rock stress and displacement, radial deformation of lining, and support reaction force was observed. At the same time, considering the effects of seepage, strain softening, and intermediate principal stress, the surrounding rock is divided into a plastic residual zone, plastic softening zone, and elastic zone, and the stress distribution expressions of the plastic zone and each zone of surrounding rock of circular tunnel are derived. The results show that with the change of nonuniform permeability coefficient, the seepage shows anisotropy in different directions, and the closer to the horizontal or vertical direction, the more obvious the influence of nonuniform permeability coefficient on pore water pressure distribution. Seepage and material softening have different effects on the distribution of surrounding rock stress field and the size of plastic zone. Material softening is more unfavorable to the stability of surrounding rock than seepage. The intermediate principal stress coefficient has a significant impact on the tangential stress and plastic zone of surrounding rock. When the intermediate principal stress effect is not considered, the calculation results are relatively conservative and cannot give full play to the strength of surrounding rock effectively. The research conclusion can provide a theoretical reference for studying the stability of surrounding rock in tunnel excavation under water-bearing rock.

Quantitative risk assessment for deep tunnel failure based on clustering and logistic regression at the Ashele copper mine, China

ABSTRACT Tunnel failure caused due to geologic heterogeneity and variability in both mining processes and tunnel arrangement in deep metal mines is very complex. In this paper, a quantitative risk assessment for deep tunnel failure was conducted using clustering and logistic regression. The study was performed by considering various representative evaluation indexes of geological conditions, mining disturbance, and microseismic (MS) data. Comprehensive Seismic Event Clustering (CSEC) methodology was used to analyse the MS data to filter noise data and identify seismic sources. Additionally, peak particle velocity (PPV) was used to quantitatively evaluate the influence of MS activities on the response of tunnel which would aid in determining the PPV distribution characteristics of a large regional tunnel. Furthermore, Excavation Vulnerability Potential (EVP) index was used to quantitatively evaluate the effect of site conditions on response of the tunnel. Thus, based on logistic regression, PPV and EVP were used to establish a risk assessment model to determine the tunnel damage levels and probability of damage occurrence. The successful application of the proposed method at the Ashele copper mine demonstrates that it is capable of conducting a risk assessment for tunnel failure in deep metal mines.

Numerical analysis for mining-induced stress and plastic evolution involving influencing factors: high in situ stress, excavation rate and multilayered heterogeneity

PurposeThis study aims to analyse the deep resource mining that causes high in situ stress, and the disturbance of tunnelling and mining which may induce large stress concentration, plastic deformation and rock strata compression deformation. The depth of deep resources, excavation rate and multilayered heterogeneity are critical factors of excavation disturbance in deep rock. However, at present, there are few engineering practices used in deep resource mining, and it is difficult to analyse the high in situ stress and dynamic three-dimensional (3D) excavation process in laboratory experiments. As a result, an understanding of the behaviours and mechanisms of the dynamic evolution of the stress field and plastic zone in deep tunnelling and mining surrounding rock is still lacking.Design/methodology/approachThis study introduced a 3D engineering-scale finite element model and analysed the scheme involved the elastoplastic constitutive and element deletion techniques, while considering the influence of the deep rock mass of the roadway excavation, coal seam mining-induced stress, plastic zone in the process of mining disturbance of the in situ stress state, excavation rate and layered rock mass properties at the depths of 500 m, 1,500 m and 2,500 m of several typical coal seams, and the tunnelling and excavation rates of 0.5 m/step, 1 m/step and 2 m/step. An engineering-scale numerical model of the layered rock and soil body in an actual mining area were also established.FindingsThe simulation results of the surrounding rock stress field, dynamic evolution and maximum value change of the plastic zone, large deformation and settlement of the layered rock mass are obtained. The numerical results indicate that the process of mining can be accelerated with the increase in the tunnelling and excavation rate, but the vertical concentrated stress induced by the surrounding rock intensifies with the increase in the excavation rate, which becomes a crucial factor affecting the instability of the surrounding rock. The deep rock mass is in the high in situ stress state, and the stress and plastic strain maxima of the surrounding rock induced by the tunnelling and mining processes increase sharply with the excavation depth. In ultra-deep conditions (depth of 2,500 m), the maximum vertical stress is quickly reached by the conventional tunnelling and mining process. Compared with the deep homogeneous rock mass model, the multilayered heterogeneous rock mass produces higher mining-induced stress and plastic strain in each layer during the entire process of tunnelling and mining, and each layer presents a squeeze and dislocation deformation.Originality/valueThe results of this study can provide a valuable reference for the dynamic evolution of stress and plastic deformation in roadway tunnelling and coal seam mining to investigate the mechanisms of in situ stress at typical depths, excavation rates, stress concentrations, plastic deformations and compression behaviours of multilayered heterogeneity.

Deformation and Strength Characteristics of Structured Clay under Different Stress Paths

In geotechnical applications such as deep foundation excavation, slope cutting, and tunnel construction, the stress state of the soil subjected to loading or unloading will change and undergo different stress paths with corresponding changes in its mechanical properties. Therefore, a series of comprehensive laboratory tests were conducted on the natural strong structured clay to evaluate the effects of stress paths on the stress-strain, pore water pressure-strain, deformation characteristics, shear strength behaviors, and the microscopic mechanism of the natural strong structured clay. The results show that the mechanical properties of structured clay under different stress paths are quite different and are closely related to its structure. The peak deviatoric stresses of the soil under both the compression path and the tensile path are affected by the stress path, and the order of its strength is INP > KCP > DEP. The variations of the pore water pressure reflect the shear dilation and the shear contraction characteristics of the soil under different stress paths; the pore pressure of the specimen is particularly complicated in the case of both axial stress and lateral stress unloading; therefore, the pore water pressure in the soil under unloading conditions should be monitored in real time in engineering practice. The stress path affects the total stress strength indices of the structured clay to a significant extent and the effect on soil cohesion is greater than that on the internal friction angle, and the microstructure of the specimens has been changed after shearing tests with different stress paths. Therefore, design calculations should be conducted according to the experimental mechanical parameters under the stress path experienced by the soil under the actual engineering conditions to ensure safety and stability during construction.

Risk Prediction of Rock Bursts and Large Deformations in YL Tunnel of the Chongqing–Kunming High-Speed Railway

The YL Tunnel of the Chongqing–Kunming high-speed railway project, a key project of the whole line, is a typical ultra-long deep tunnel facing geologic problems, such as rock bursts, large deformation, water inrush, and toxic or harmful gas leakage, among which high ground stress results in the most serious damage. This study incorporates existing studies and materials, as well as data on ground stress obtained through tests using the hydrofracturing technique. The areas with rock bursts and large deformations were divided accordingly, and preventive measures were expounded. The results showed that the areas predicted as high risk of severe rock burst were D1K338 + 945–D1K339 + 025 and D1K339 + 075–D1K339 + 220, which is of significance when constructing the whole Chongqing–Kunming high-speed railway and may even be instructive in railway construction in the southwest region of China.

Numerical and Machine learning modeling of hard rock failure induced by structural planes around deep tunnels

The Rockburst phenomenon is one of the hazards in deep underground mines and tunnels that can be exacerbated by faults or structural features. An accurate understanding of this phenomenon can control or reduce its destructive impacts. Using methods that can accurately estimate or predict this phenomenon is a critical issue for experts in the field. Since studying rockburst with the help of laboratory and numerical methods is a complex issue and, at the same time, requires high time and cost, in this paper, the machine learning method of extreme gradient boosting (XGBoost) was used for predicting this phenomenon. For this purpose, numerical modelling was used in the Abaqus software environment to generate 300 datasets. A fault around the modelled tunnel was considered to show the impact of faults on the phenomenon of rockburst in tunnels. The datasets included 13 effective input parameters on the rockburst phenomenon. Among the 300 datasets, 250 data were used for training and 50 data for the test. The comprehensive results indicated that the XGBoost model has the potential ability to estimate the rockburst phenomenon that may occur during deep tunnelling near fault zones. The results revealed that faults around deep tunnels could significantly increase the risk of rockburst if the fault is positioned and oriented in such a way that it promotes high stress. The MIT method revealed that, among the 13 input parameters considered in this study, fault length and density have the most and least impact on the rockburst phenomenon, respectively. Finally, to have good knowledge of the rockburst phenomenon in tunnelling projects, this article recommends using the XGBoost method to predict the rockburst in deep tunnels near the fault zones. The importance of the proposed model is that it can provide a reasonable estimate of the rockburst phenomenon in the deep tunnels, based on which geotechnical engineers can take the necessary measures to deal with it in the pre-construction designs.

Analytical Solution for Seismic Response of Deep Tunnels with Arbitrary Cross-Section Shape in Saturated Orthotropic Rock

Analytical Solution for Seismic Response of Deep Tunnels with Arbitrary Cross-Section Shape in Saturated Orthotropic Rock

Evaluation of the Effect of Geomechanical Parameters and In Situ Stress on Tunnel Response Using Equivalent Mohr-Coulomb and Generalized Hoek-Brown Criteria

The generalized Hoek-Brown (GHB) failure criterion can estimate the rock mass parameters required for rock mechanics–related analyses such as numerical modeling in geomechanics. The determination of GHB parameters has been developed in the field of rock mechanics. Due to the wide use of the Mohr-Coulomb criterion and the lack of an existing relationship for determining its parameters for a rock mass, equivalent Mohr-Coulomb parameters (EMC) can be derived from the GHB. To determine the differences in the use of these two criteria, we analyzed the behavior of a deep circular tunnel in nine stress states for three metamorphic rocks recovered from the Canadian Shield from rock masses that present a very blocky structure. We carried out 241 simulations using the finite element code RS2 to assess the effect of the geological strength index (GSI), in situ stress, and rock type on the deviation of wall displacement, the number of yielded elements, and the differential stress obtained by the GHB and EMC parameters. A combination of low in situ stress and high GSI yielded similar results when using both failure criteria.

Development and Occurrence Mechanisms of Fault-Slip Rockburst in a Deep Tunnel Excavated by Drilling and Blasting: A Case Study

Development and Occurrence Mechanisms of Fault-Slip Rockburst in a Deep Tunnel Excavated by Drilling and Blasting: A Case Study

Coherent state representation of thermal correlation functions with applications to rate theory.

A coherent state phase space representation of operators, based on the Husimi distribution, is used to derive an exact expression for the symmetrized version of thermal correlation functions. In addition to the time and temperature independent phase space representation of the two operators whose correlation function is of interest, the integrand includes a non-negative distribution function where only one imaginary time and one real time propagation are needed to compute it. The methodology is exemplified for the flux side correlation function used in rate theory. The coherent state representation necessitates the use of a smeared Gaussian flux operator whose coherent state phase space representation is identical to the classical flux expression. The resulting coherent state expression for the flux side correlation function has a number of advantages as compared to previous formulations. Since only one time propagation is needed, it is much easier to converge it with a semiclassical initial value representation. There is no need for forward-backward approximations, and in principle, the computation may be implemented on the fly. It also provides a route for analytic semiclassical approximations for the thermal rate, as exemplified by a computation of the transmission factor through symmetric and asymmetric Eckart barriers using a thawed Gaussian approximation for both imaginary and real time propagations. As a by-product, this example shows that one may obtain "good" tunneling rates using only above barrier classical trajectories even in the deep tunneling regime.

Study on the Surrounding Rock Pressure Characteristics of Loess Tunnel Based on Statistical Analysis in China

A method of load calculation in a tunnel was adopted in consideration of the state of covering depth. Due to the macropore characteristics of loess soil, the existing demarcation regulations of deep and shallow tunnels are inappropriate for large-section and shallow loess in highway tunnels. To determine the load of large-section loess tunnel and provide a proper reference for structural design, the theoretical basis for distinguishing depth of deep and shallow tunnels, as well as the characteristics of common calculation methods for surrounding rock load on depth, were analyzed. Through statistical analysis and significance analysis, the significance of the variation of surrounding rock pressure with cover depth was studied. Correlation analysis was carried out on significant results to fit the relationship between cover depth and surrounding rock pressure. The results showed that the surrounding rock pressure varied linearly with the cover depth, and the surrounding rock pressure was about 0.3 times the initial pressure in deep tunnels. The surrounding rock pressure of shallow tunnels did not change significantly with the cover depth, and the surrounding rock pressure was loose pressure. A method based on statistics was proposed to distinguish the cover depth threshold (CDT) of deep and shallow tunnels.

Analytical solution of external water pressure on deep tunnel lining in horizontally layered hydrogeological structures

Analytical solution of external water pressure on deep tunnel lining in horizontally layered hydrogeological structures