Deep-buried Tunnel Research Articles

Peridynamics simulation of surrounding rock damage characteristics during tunnel excavation

The improved peridynamics is introduced to analyze the stability of surrounding rock in tunnel excavation process. By introducing short-range repulsive force into peridynamic equation of motion, the tensile and compression failure characteristics of rock materials is simulated. In order to simulate the process of tunnel excavation, the material point dormancy method is proposed in this paper. By simulating the distribution characteristics of excavation damage zone (EDZ) during the excavation of a circular tunnel with high stress difference, the relationship between the distribution position of EDZ and the direction of maximum principal stress is revealed. The v-shaped notches developed on the tunnel periphery at the direction of perpendicular to the maximum principal stress. The predicted EDZ distribution characteristics is consistent with the results of previous studies. And the displacement field of surrounding rock after tunnel excavation is also in good agreement with FEM simulation result. The simulation results show that this method not only has good stability, but also has high computational efficiency. By analyzing the deformation, damage and failure characteristics of surrounding rock under different buried depths, different lateral pressure coefficients, different excavation methods and different section shapes, the evolution process of rock instability caused by tunnel excavation and unloading is revealed. Which provides reference for the design and optimization of surrounding rock support scheme in deep buried tunnels.

Research on construction method and deformation control technology of high ground stress interbedded soft rock tunnel

The construction of tunnels is often long and deep buried tunnels, and the geological conditions are more complex. Based on Jianshan tunnel in Gansu Province, the special geological conditions such as high ground stress and weak interbedded surrounding rock make the excavation of tunnel easy to produce large deformation. In this article, the software finite difference software FLAC3D was used to establish numerical models and select the best construction method by comparing the deformation of the tunnel under different construction methods. Aiming at the deformation characteristics of soft rock tunnels in highland interbedded layers, the control measures of tunnel deformation are discussed. Mainly consider the two aspects of the bolt support plan and the second lining construction time, comprehensively compare the deformation characteristics of the tunnel, and select the best working condition. The research results show that the combination of three-step temporary invert method and three-step ultra short bench method is recommended for the tunnel construction; when the bench length is 4 m, the deformation control effect of the tunnel is the best; by improving the length and angle of the anchor rod, the deformation of the tunnel can also be well controlled.

Analysis on Loose Circle of Surrounding Rock of Large Deformation Soft‐Rock Tunnel

With the rapid development of tunnel construction in China, deep buried and long tunnel projects are emerging in areas with complex engineering geological conditions and harsh environment, and thus large deformation of tunnels under conditions of high in situ stress and soft rock becomes increasingly prominent and endangers engineering safety. Therefore, it is of great significance to control the deformation and improve the stability of surrounding rock by analyzing the thickness and distribution law of loose circle according to the unique mechanical properties and failure mechanism of surrounding rock of large deformation soft‐rock tunnel. Based on unified strength theory, this paper deduces the radius calculation formula of the loose circle by considering the influence of intermediate principal stress. Furthermore, the theoretical calculations and field tests of the loose circle in the typical sections of grade II and III deformation of Yuntunbao tunnel are carried out, and the thickness and distribution law of loose circle of surrounding rock of large deformation soft‐rock tunnel is revealed. The results show that the formula based on the unified strength criterion is applicable for a large deformation tunnel in soft rock.

Effects of Different Interface Forms on Mechanical Properties of Steel Self‐Compacting Concrete Composite Beams

In the water resources allocation project in Pearl River Delta, in order to optimize the structural design, the deep buried tunnel adopts the composite lining structure. However, the weakest link in a complex structure is the connection between two different interfaces. This paper reports the findings of an experimental study that was undertaken to investigate the interface mechanical performance of steel self‐compacting concrete composite structure subjected to cyclic loads. In this study, different shear connectors are considered, and six different specimens were designed and tested, respectively. The test is used to research the effect of the different shear connectors on the bearing capacity and interface mechanical properties of composite structure in an experimental study. According to these test results, a detailed analysis was carried out on the relationships, such as the stress‐strain and load‐displacement relationships for the specimen. These tests show that the shear connectors will significantly enhance the bearing capacity and interface mechanical properties of the composite structure. Among them, the comprehensive performance of the specimens using the stud‐longitudinal ribs shear connectors is the best. Additionally, a finite element analysis (FEA) model was developed. The comparison of the simulation results with the experimental results shows that this FEA is applicable for this type of experiment.

Post-peak deformation and failure behaviour of Jinping marble under true triaxial stresses

The post-peak behaviour of rocks plays an important role in studying the stability of surrounding rocks. A series of true triaxial compression tests in high-low stress states were carried out on 58 Jinping marble specimens. The characteristics of complete stress–strain curves, including the post-peak stage, the corresponding meso- and micro-failure characteristics with scanning electron microscopy (SEM), and the whole progressive failure processes with acoustic emission (AE), were analysed. With either decreasing σ3 or increasing σ2, the shapes of the post-peak curves change from Class I to Transition and then to Class II. Additionally, the changes have obvious stress boundaries. As σ2 increases at low-constant σ3 or σ3 decreases at constant σ2, the failure mode changes from tensile–shear mixed failure or shear failure to tensile failure, and these changes correspond with the changes in the post-peak curves. Micro-failure of marble changes from intergranular failure at Class I to transgranular failure at Class II. The AE characteristics of the three typical post-peak progressive failure processes are significantly different, matching the brittle failure behaviour from weak to strong. This study enhances the knowledge of in situ failure mechanisms and the stability of deep-buried tunnels and caverns.

Visualization Analysis for Tunnel Researches Based on CiteSpace

In order to find out the history, present situation and hot trend of tunnel research, this article is based on the literature data of tunnel study from 1997 to 2017 in CNKI database, using CiteSpace visual econometric analysis software to co-occurrence analysis and keyword co-word analysis and processing by citation data of authors and research institutions. The results showed that there is close cooperation among the authors of the main research groups, haveing a good cooperative relationship chain among the research institutions, and the keywords of hot research are diversion tunnel, deep buried tunnel, numerical simulation, water conveyance tunnel, lining, rock burst, rock mechanics, surrounding rock, river diversion tunnel, TBM and so on.

Analytical solution for stress distribution around deep lined pressure tunnels under the water table

Existing models on the stress distribution around deep buried tunnels pay little attention to the impact of rock-liner interaction and seepage variation. The conventional solution for deep lined tunnels has an inherent mathematical restriction since it is limited to thin liners. In this paper, we solve the poro-mechanical problem of stress and pore pressure distribution using the complex variable method and the conformal mapping technique. The proposed solution relaxes the assumptions of thin liner and negligible stresses that limit the usefulness of existing approaches. To derive the solution, the stress function is expanded into Laurent series in the complex plane. Analytic expressions for both with and without gravity conditions are obtained. The proposed solution is compared with the Finite Element Method; a good agreement has been obtained between the numerical simulations and proposed analytical solution. It is found that with the liner installation, the effective maximum principal stress (MPS) decreases by about 50% for the given case condition. In addition, the pore pressure distribution around the tunnel increases sharply compared to the no liner condition. The parametric study shows that the effective MPS value is highly affected by the liner relative thickness, stiffness and permeability. Its location on the tunnel boundary moves from the horizontal direction to the invert with the increase of the liner thickness and stiffness. Furthermore, the results show that low liner permeability results in high pore pressure around the tunnel, which reduces the effective stress within the rock mass.

Mechanical Parameter Inversion in Sandstone Diversion Tunnel and Stability Analysis during Operation Period

A large number of experimental studies show that the mechanical parameters of deep buried surrounding rock show significant attenuation characteristics with the increase of strain from the rheological acceleration stage to the attenuation stage. However, the existing numerical models all take mechanical parameters as constants when describing the rheological behavior of surrounding rocks, which can only be applied to the stability analysis of the shallowly buried tunnel. Therefore, this work proceeding from the actual project, improved the sandstone rheological constitutive model and optimized the algorithm of parameter inversion, and put forward a long-term stability analysis model that can accurately reflect the rheological characteristics of surrounding rocks under the complex geological condition including high stress induced by great depth and high seepage pressure. In the process, a three-dimensional nonlinear rheological damage model was established based on Burgers rheological model by introducing damage factors into the derivation of the sandstone rheological constitutive model to accurately describe the rheological behaviors of the deep buried tunnel. And BP (Back Propagation) neural network optimized by the multi-descendant genetic algorithm is used to invert the mechanical parameters in the model, which improves the efficiency and precision of parameter inversion. Finally, the rheological equation was written by using parametric programming language and incorporated into the general finite element software ANSYS to simulate the rheological behavior of the tunnel rock mass at runtime. The results of the model analysis are in good agreement with the monitoring data in the later stage. The research results can provide a reference for the stability analysis of similar projects.

Numerical Simulation to Research on the Fracture Mechanism of the Surrounding Rock in Deep Tunnels

In order to further explored the mechanical mechanism of surrounding rock zonal disintegration in deep buried tunnels, Numerical simulation was used in this paper to analyze the variation of different rock mass mechanical parameters (c, φ, µ) of surrounding rock and variation of the zonal disintegration under horizontal tectonic stress. Through the research and analysis, the influence law of rock mass mechanical parameters (c, φ, µ) on the zonal disintegration of surrounding rock of deep buried tunnel was obtained. The increase of the cohesive force and internal friction angle of the rock mass can reduce the range of partition failure. However, the influence of Poisson’s ratio on the zonal disintegration range presents nonlinear characteristics. At the same time, the horizontal tectonic stress directly determines whether the zonal disintegration phenomenon occurs, and it is the key factor for the regional failure of the surrounding rock of the deep tunnel. The above conclusions had certain reference value for in-depth study of the failure problem in deep buried tunnels, and provided theoretical support for further discussion of its mechanical mechanism.

Analytical analysis of stress and displacement for surrounding rock of deep-buried rectangular tunnel in layered strata

This study presents a theoretical solution on stress and displacement of the deep-buried tunnel surrounding rock in layered strata. Based on theory of Покровский equivalent layer method, we convert layered strata into homogeneous ones and then map the rectangular tunnel in the coordinate plane z to the unit circle of complex plane ζ, through using a complex variable method and calculating the analytic functions Φ(ζ) and Ψ(ζ) with Matlab, the study obtains that the stress of the surrounding rock of deep-buried rectangular tunnel in layered strata. Subsequently, we derive the strain and displacement of the surrounding rock. Finally, we study the effects of lateral pressure coefficient and grade of surrounding rock and height-to-width ratio of the tunnel on the stress of tunnel surrounding rock. Based on our analysis, we formulate valuable rules.

Limit Analysis of Progressive Asymmetrical Collapse Failure of Tunnels in Inclined Rock Stratum

Tunnels commonly pass through inclined rock stratum, but research on the collapse of the rock surrounding the tunnels in inclined rock strata is currently underdeveloped. The purpose of this study was to predict the progressive asymmetrical collapse failure of deep-buried tunnels in inclined rock strata to decrease the risk of collapse during tunnel construction. We constructed a new two-dimensional progressive asymmetrical collapse failure mechanism for deep-buried tunnels in inclined rock layers to analyze their collapse failure characteristics with the help of the nonlinear Hoek–Brown yield criterion and the limit analysis theorem. The calculation equations of the range and total weight of the asymmetrical collapsing block in rectangular and circular tunnels were obtained via theoretical derivation. The validity of the proposed method in this work was verified by comparison with existing research. To discuss the impact of different parameters on the range and total weight of an asymmetrical collapsing block of the surrounding rock in inclined rock stratum, the range and total weight of the asymmetrical collapsing block of the most common rectangular and circular tunnels under the varied parameters are provided. The results of this study can provide useful support for practical tunnel construction and design.

A Case Study on the Asymmetric Deformation Characteristics and Mechanical Behavior of Deep-Buried Tunnel in Phyllite

When tunneling through deep-buried layered soft strata, asymmetric deformation of surrounding rock and asymmetric mechanical behavior of supporting structures are often encountered. This paper investigates the anisotropic mechanical properties of deep-buried carbonaceous phyllite and its influence on the asymmetrical mechanical behavior of supporting structures in the Zhegu mountain tunnel in Sichuan Province, China. It is a typical road tunnel that suffered from large asymmetrical deformation and cracking of the secondary lining due to layered strata and high geo-stresses. Firstly, experimental tests were conducted to investigate the influence of bedding angle on the mechanical properties and failure behavior of phyllite. Then, the UDEC numerical software was adopted to study the effects of the lateral pressure coefficient, rock layer inclination angle, bedding spacing and shear stress on the mechanical behavior of supporting structures. Moreover, a field test was conducted to measure the pressure between the surrounding rock and the primary support as well as the internal force of the steel arch and the secondary lining. Based on the field data and numerical simulation results, it can be concluded that the asymmetrical deformations of surrounding rock and the cracking of secondary lining in the Zhegu mountain tunnel were results of the coupling effect of layered soft rock and shearing action along the foliation.

Physical and Mechanical Characteristics of Soft Rock Tunnel and the Effect of Excavation on Supporting Structure

The problem of large deformation is very prominent in deep-buried tunnel excavation in soft rock, which brings serious potential safety hazards and economic losses to projects. The knowledge of deformation law and support measures is the key to ensure the rational design and safe construction in a large deformation tunnel of soft rock. This paper describes rock physical and mechanical tests and field monitoring is employed to investigate the cause and development process of large deformation in Dongsong hydropower station in Sichuan Province, China. The results show that the free expansion rate of the rock sample is 20.0%, the average expansion stress of the rock sample is 11.0 kPa, and the expansibility of the rock is low. Large deformation of surrounding rock mainly comes from the dilatancy effect with high geostress and relaxation deformation with weak support. Shotcrete sealing exposed surrounding rock, and early strength support avoiding water immersion are useful to deal with the three main factors (weathering, water and confining pressure) that affect the strength of surrounding rocks. The second lining applied in time can effectively limit the further development of stress and deformation of initial support, and prevent the cracking and large deformation of concrete. Clearance convergence is suggested to be the main monitoring work in construction, because of its advantages of intuitive results, easy quality assurance of instrument installation and high accuracy.

Parameter Optimization for the Thickness and Hydraulic Conductivity of Tunnel Lining and Grouting Rings

Water inrush is a serious geological hazard in the deep buried tunnel construction in karst areas. Lining and grouting ring are often built to prevent tunnel from water inrush. The estimation of external water pressure and water inflow is of great significance to the structure design of lining and grouting ring. In this paper, the axisymmetric analytic solutions of external water pressure and water inflow were derived for deep karst tunnels under saturated steady-state flow conditions. A simplified formula for the reduction coefficient of external water pressure was established. This paper analyzed the changing rule of water inflow coefficient and the reduction coefficient of external hydraulic pressure on linings, which varies with the parameters of lining and grouting circle. The rational and available coefficients of grouting circle in karst deep buried tunnel construction are drawn: the grouting ring thickness is 6 m and the hydraulic conductivity ratio of surrounding rock and lining is 100. In addition, the accuracy of the simplified formula was verified by the comparison of analytical solution and numerical analysis. This study provides a reliable calculation method for water inflow and lining water pressure of the deep buried tunnel and have certain reference value for the structural design of deep buried tunnel to reduce water inflow and ensure construction safety.

Study on Mechanism of Segmental Lining-Bolt Combined Support for Deep-Buried Tunnel

Segmental lining-bolt combined support is extensively applied in mechanized shield tunneling for deep tunnel. In order to reveal the mechanism of segmental lining-bolt combined support, a true three-dimensional geo-mechanical model test and numerical simulation study are conducted on the background of Xianglushan Tunnel in the Yunnan Water Diversion Project. The research results show that: (1) the mechanism of segmental lining-bolt combined support includes two aspects: “load bearing effect” and “protection and reinforcement effect”. The segmental lining is a kind of rigid support and mainly plays a load-bearing role. The bolt reinforces and protects the surrounding rock, whose load-bearing effect is not obvious; (2) the fault has a distinct influence on the bearing capacity of the surrounding rock. The loads taken by the surrounding rock and the support is significantly different under different geological conditions; (3) the plastic zone causes the surrounding rock stress to move to deep rock mass, which induces the formation of pressure arch. The larger the size of plastic zone is, the larger the range of pressure arch formed in deep rock mass is, and the farther the distance from pressure arch to tunnel wall is. The plastic zone is the necessary condition for the formation of pressure arch. The research results can provide the basis for the establishment of construction scheme and the optimization of support design for large buried tunnel under complex geological conditions.

Thermal Diffusion Effects in a Tunnel with a Cylindrical Lining and Soil System under Explosive Loading

An analytical method is employed to study the thermoelastic dynamic response of deep-buried circular tunnel lining-soil system under explosion load, considering thermal diffusion effects. The soil and lining are analyzed as homogeneous elastic media. Based on the generalized thermal diffusion theory and the classical thermal elasticity theory, the thermoelastic dynamic response of a soil-lining system in the event of an explosion is solved using the Laplace transform and Helmholtz decomposition. By using continuity boundary conditions, the corresponding numerical solution is obtained through an inverse Laplace transform. The calculated results are compared to those without the lining and without consideration for the diffusion effect. The effects are analyzed under thermal, mechanical, and chemical coupling of the lining and soil properties, and their geometric parameters on the temperature gradient, displacement, stress, and chemical potential of the system. It provides significant guidance for theoretical calculations and antiexplosion design of the lining tunnel.

Stress Field Distribution and Deformation Law of Large Deformation Tunnel Excavation in Soft Rock Mass

The problem of large deformation is very prominent in deep-buried tunnel excavation in soft rock, which brings serious potential safety hazards and economic losses to projects. Knowledge of the stress field distribution and deformation law is the key to ensuring rational design and safe construction in large deformation tunnels of soft rock. As described in this paper, theoretical analysis, numerical simulation and field monitoring were employed to investigate the surrounding rock stress and displacement state in the Dongsong hydropower station in Sichuan Province, China. The results show that the short-bench construction method can effectively control the deformation of surrounding rock and range of the plastic zone. In order to reserve enough working space, the optimum bench length in the actual construction was 10 to 14 m. The peripheral displacement and plastic radius decreased with the increase of tunnel support strength and the advance of supporting time. The displacement can be effectively controlled by applying the second lining in time at a position about twice the diameter of the hole (16 m) from the working face. A reasonable reserved deformation should be adopted to avoid secondary expanding excavation. The values of different positions in the tunnel laterally and longitudinally may be different, and adjustments are needed according to the actual situation.

Supporting mechanism and mechanical behavior of a double primary support method for tunnels in broken phyllite under high geo-stress: a case study

Large squeezing deformation has always been a critical concern in the construction of deep-buried tunnels in soft-weak rock masses. This paper describes a case study on the large deformation mechanism and supporting method of the Maoxian tunnel in Sichuan Province, China, which is located in the core area influenced by the 2008 Wenchuan earthquake and suffered severe large deformation in broken phyllite under high geo-stress. Through a survey on the geological features, the deformation mechanism of surrounding rock and the failure characteristics of supporting structures of the Maoxian tunnel in F1 fault zone were studied. It was found that the occurrence of large deformation was due to the combined action of the high geo-stress and poor self-stability of carbonaceous phyllite. In order to control the squeezing deformation, single and double primary support methods were adopted in succession. A comparative field test was conducted to study their supporting mechanism and mechanical behavior in terms of surrounding rock pressure, internal stress of the steel arch, and axial force and bending moment of the secondary lining. The results revealed that the single primary support method cannot ensure the long-term safety of the tunnel, since many cracks in concrete occurred after about 180 days. The double primary support method, however, was able to control the large deformation and rheological effects of broken phyllite under high geo-stress effectively.

Analysis of stress evolution characteristics during TBM excavation in deep buried tunnels

Full-face tunnel boring machines (TBMs) are widely used in tunnel engineering projects as an efficient, safe and economical tunneling method. However, TBM excavation causes stress near the tunnel boundary that is disturbed and redistributed under high in situ stress. The changing stress of the surrounding rock can lead to rock failure and cause machinery damage, owing to large rock mass deformations. Research on the impact of TBM excavation on the surrounding rock has mostly focused on the stress magnitude, while the influence of the variation of stress orientation has not been considered. In this study, the practical simulation of a double-shield TBM (DSTBM) construction process was conducted using a three-dimensional (3D) numerical simulation. The rock mass stress changed intensely with the rotations of the principal stress axes as the tunnel face passed through the rock monitoring section during the tunnel excavation. Additionally, the significant influence of stress variation is discussed in qualitative terms, and the analysis results of the stress path are presented. Moreover, using a new self-developed laboratory apparatus, the actual stress path of the surrounding rock is proposed under conditions of a changing principal stress magnitude and changing rotation of the principal axis during the process of TBM excavation.

Analytical Solution for the External Stress Acting on the Lining in a Deep-Buried Circular TBM Tunnel Considering the Seepage Field

Analytical Solution for the External Stress Acting on the Lining in a Deep-Buried Circular TBM Tunnel Considering the Seepage Field