Stability Analysis Of Tunnel Research Articles

Face stability analysis of large diameter shield tunnel in soft clay considering high water pressure seepage

The aim of this paper is to study the influence of high water pressure seepage on the stability of large diameter shield tunnel face in soft clay. Based on allowable displacement rate field of the established double logarithmic spiral collapse body, the theoretical solution of limit support force of large diameter shield tunnel face under seepage was derived, the theoretical solutions of limit support force under different water levels were verified. And the influence of water levels and internal friction angles on the stability of large diameter shield tunnel face under seepage was also analyzed. The results show that the seepage force is the main part of the total limit support force. The influence of seepage on the stability of large diameter shield tunnel face in theoretical analysis can be regarded as seepage force on tunnel face and pore water seepage force in collapse body. The seepage effect in collapse body can be considered as the downward seepage in soil layer above the tunnel face, and the horizontal seepage in soil layer where the tunnel face is located. The influence of water levels and soil internal friction angles on the face stability is obvious when considering seepage effect.

Upper-Bound face stability analysis of rectangular shield-driven tunnels in undrained clays

The face stability of rectangular shield-driven tunnels in undrained clays where the undrained shear strength increases linearly with depth is investigated numerically and analytically in this paper. In the framework of the kinematic approach of limit analysis, two new failure mechanisms based on the translational movement of rigid blocks and continuous deformation of soil mass are proposed for collapse and blowout cases. The analytical solutions of the failure mechanisms were compared with those of finite element simulations and the existing approaches in the literature to evaluate their validity and productivity. The critical support pressures obtained from the analytical models are relatively consistent with the results of the numerical simulations for square and wide rectangular tunnels. Simple design formulas were provided for analytical models to compute the limit support pressure for practical use. Finally, parametric studies were performed to explore the impact of different geometrical and geotechnical parameters pertaining to the stability of the tunnel face.

Influence of blasting load directions on tunnel stability in fractured rock mass

Tunnels in fractured rock masses are typically damaged by dynamic disturbances from various directions. To investigate the influence of blasting load directions on the stability of a tunnel with a pre-crack nearby, blasting tests were conducted on the physical models of an external crack around a tunnel (ECT) in this study. Failure modes of the tunnels were analysed based on stress wave theory. The Riedel–Hiermaier–Thoma (RHT) material model was employed to perform the numerical simulations on ECT models. Stress distribution around the tunnels and final failure patterns of the tunnels were characterised. The results show that, under blasting loads, the pre-crack propagates and then new cracks initiates on the incident side of the tunnel. These cracks extend towards each other and eventually coalesce. Blasting load directions significantly influence the ultimate failure mode of the tunnel in the fractured rock masses. The new cracks on the shadow side of the tunnel appear at different positions when the blasting stress waves come from various directions. The results are meaningful to the analysis of tunnel stability and optimisation of the tunnel support scheme.

Stability Analysis of Tunnel by External Force Increment Method

A new tunnel stability analysis method is proposed which is the external force increment method (EFIM) to transform the traditional tunnel stability ratio (<I>N</I>). The EFIM can be defined as the field stability raito (<I>N</I>_f), which consists of two newly defined parameters, namely the natural stability ratio (<I>N</I>_n) and the critical stability ratio (<I>N</I>_c). The relationship between the field stability ratio (<I>N</I>_f) and the change of external force is given. The tunnel stability plane and tunnel stability analysis plot are constructed. Based on this, the relationship between the field stability ratio (<I>N</I>_f) and the critical stability ratio (<I>N</I>_c) when the initial tunnel is stable or unstable is determined. According to the field stability rate (<I>N</I>_f), the critical stable state can be achieved with the tunnel by increasing two ways: one is to increase the external load to act on the external force on the tunnel, and the other is to reduce the internal support force of the tunnel. The relations for reaching the critical stability ratio (<I>N</I>_c) of the two EFIM are given respectively. The upper bound solutions of single tunnel, twin tunnels with the same diameter and twin tunnels with different diameters are analyzed by this method. The results show that the EFIM is reasonable and feasible for stability analysis of tunnel.

Stability Analysis of Directional Tunnel in Sandy Soil

In recent times, water storage is becoming a confronting task because of the depletion of water resources worldwide. Domestic rainwater harvesting and human-made structures for water procurement achieved significance because of the increase in intermittent water accessibility. In turn, functional water infrastructures fetch prominence in the wake of constructive coordination among the communities in a locality. Low water security and losses through evaporation observed by practising different rainwater harvesting methods create a research gap to construct water infrastructure in rural areas to procure water productively. The current research work represents the model of a water storage structure, named directional tunnel (DT), which is placed below the ground level in a declination, as it reduces evaporation and temperature, thus storing rainwater for longer days. DT stores runoff and rainwater collected from the rooftop of multiple houses in a selected locality. The detailed working of the DT is discussed using Building Information Modelling (BIM) concept. Combined with the engineering geological characteristics, the DT’s stability during water storage comes into the picture as the whole structure interacts with the soil. The current study also focuses on the behaviour of DT with respect to sandy soil using PLAXIS 3D software, and the results are interpreted for practical viability.

Three-Dimensional Face Stability Analysis of Deep and Shallow Tunnels in Rock Masses

Face stability is a critical issue in the stability analysis of tunnels, especially in soft soils and crushed rock masses. In this paper, considering two three-dimensional collapse mechanisms, upper-bound solutions are presented for determining the face pressure of deep and shallow tunnels excavated in rock masses. The Hoek–Brown failure criterion was considered for the rock mass surrounding the tunnel. The proposed upper-bound formulations were compared with three-dimensional finite-element simulations and also with centrifuge test results available in the literature. The obtained results showed that the face pressure decreases with increasing σci, mi, and geological strength index. Besides, increasing the tunnel diameter and the rock mass density led to an increase in the face pressure, where for larger tunnels, the effect of the density became more pronounced. Finally, some charts were presented to specify the range of applicability of the concepts of deep and shallow tunnels. The results obtained from these charts demonstrated that the reduction in the Hoek–Brown parameters of the rock mass results in spreading the collapse mechanism from the tunnel face to the ground surface.

Effect of high temperature and confining pressure on the mechanical behavior of granite from Batang fault zone

The mechanical behavior of rocks under high temperature and confining pressure contributes to the design and stability analysis of deep-buried tunnels. In this study, a series of triaxial compression tests with high temperature and confining pressure was conducted on granite samples through a self-developed high temperature true triaxial test system. The granite samples were collected from the Batang fault zone located at the eastern of the Qinghai-Tibet Plateau. Based on the actual geological conditions, three temperatures (room temperature/70°C/110°C) and the confining pressure of 30 MPa were used. The stress–strain output, peak stress, and peak strain were summarized, and the relationship between the peak stress and temperature was obtained based on the experimental data. The results of the test show that high temperatures can weaken the mechanical properties of granite. The peak stress of the granite is decreased with the increase in temperature. A linear function can describe the strength behavior of the granite being studies at different temperatures. The experimental data obtained in this study can be used as basic parameters for the construction and stability evaluation of the deep-buried tunnels near the Batang fault zone.

Undrained Stability Analysis of Shallow Tunnel and Sinkhole in Soft Clay: The Cavity Contraction Method

This paper presents theoretical methods for the undrained stability analysis of shallow tunnels/sinkholes in clay based on the cavity contraction theory, with some assumptions and simplifications. To examine the accuracy and reliability of the new methods, a database was assembled, which consists of stability numbers of tunnel/sinkholes in clays from 22 centrifuge model tests, 10 field tests, and 62 FELA results. It is shown that the proposed methods give an average of 2.5% overestimation for the stability numbers from model tests and is in a good agreement with the FELA results. The cavity contraction theory-based methods are then discussed, which could provide useful guidance for designers to roughly assess shallow tunnel/sinkhole stability in clays.

A Possible Tunnels Execution Technology on Subsection E2 of the Highway A1

Abstract The paper aims to establish the design elements of the tunnels to be executed on subsection E2 of the Lugoj-Deva highway section, an integral part of the A1 highway. From the multitude of problems related to the execution of a tunnel, the paper investigates the following aspects: geotechnical investigations of the areas to be crossed by tunnels, analysis of tunnel stability, static checks of the final support/lining and, finally, a possible technology for their execution.

Stability Analysis and Protection Measures of Large Section Tunnel in Coal Rich Weak Rock Stratum

Due to poor engineering geological conditions of Liujiazhuang tunnel on Shanghai-Kunming Passenger Dedicated Line, the large deformation of weak rock occurs repeatedly during tunnel construction. In this paper, the large-scale finite element software ABAQUS is used to simulate the construction process of a large-section tunnel in weak surrounding rock. It is found that when tunnel face passes through the coal seam, the displacement and stress simulated by the bench method increase abruptly. The maximum stress reaches up to 18 MPa, and displacement reaches 45 mm, which is about twice when without crossing coal seam. It is technically feasible to use the bench method for tunnel construction, under the condition when large settlements is allowed; additionally, the bench method has better technical and economic benefits than that of the CD method. Through the comparative analysis of onsite monitoring data and numerical simulation results, it can be seen that the tunnel is in a dangerous state when passing through the coal seam and measures such as strengthening support or auxiliary advance support should be taken immediately to control the surrounding rock and to ensure tunnel construction safety.

Fracture mechanism of rock around a tunnel-shaped cavity with interconnected cracks under blasting stress waves

The existence of cracks in the surrounding rock significantly affects tunnel stability under dynamic disturbances. To study the fracture mechanism of tunnels in fractured rock masses under blasting stress waves, a new specimen, i.e., the specimen with a tunnel-shaped cavity and interconnected cracks (TCIC), was proposed in this paper. Using these specimens, blasting tests were conducted. The crack propagation data were monitored by crack propagation gauges (CPGs) and strain gauges (SGs). The Riedel-Hiermaier-Thoma (RHT) model was used to perform equal-scale numerical simulations on TCIC specimens. The stress distribution and fracture modes around the tunnel in a fractured rock mass under blasting stress waves were characterised. The results show that the interconnected cracks have an important influence on the dynamic response of the tunnel under blasting stress waves. The stress distribution around the tunnel remarkably changes due to the existence of the interconnected cracks, resulting in the initiation and propagation of these cracks, but there is no fracture on the tunnel boundary. The dynamic crack propagation behaviours are influenced by the incident direction of the blasting stress wave. The crack propagation velocity in the front blasting side of the tunnel is higher than that in the back blasting side. The research results are significant to the analysis of tunnel stability and the support design.

The Application of the Strength Reduction Shortest Path Method to the Stability Analysis of Shallow Buried Tunnel

To improve the theoretical analysis of surrounding rock stability of shallow buried tunnels. The strength reduction shortest path theory is applied to the stability analysis of shallow buried tunnel surrounding rock, combined with the ultimate equilibrium strength reduction theory. We discussed the influence of the depth and span ratio of tunnel, cohesion, and internal friction angle on the shortest path of the strength reduction, and studied the effects of various factors on shallow buried tunnel safety relationship by using strength reduction factor of safety and the shortest path of the shallow buried tunnel surrounding rock and the grey relational analysis theory. The results show that: in the analysis of shallow buried tunnel in strength reduction, the approximate distribution obeys parabolic between reduction path length and the reduction ratio. When the strength reduction of cohesion is the shortest path the reduction rate is greater than the internal friction angle. The internal friction angle and cohesive force have a great influence on the stability of shallow tunnels under the method of shortest path of strength reduction. Finally, the comprehensive safety factor of shallow buried tunnels calculated by the finite element strength reduction shortest path method is greater than that calculated by the limit equilibrium method.

Study on stability of portal section of High Slope Tunnel Based on numerical analysis

Due to the complexity of the portal section of high slope tunnel, unsafe accidents are prone to occur. Because of its convenience and accuracy, numerical simulation method is often used in tunnel stability analysis. In this paper, the excavation process of the slope and tunnel at the entrance of the tunnel is simulated by using the finite element software MIDAS-GTS, taking the No.6 tunnel project of the Kovi-Agvida E60 Highway Line in Georgia as an example. According to the results of numerical calculation, although the excavation volume of the slope is large, the displacement is small and the stability is good; the deformation of the surrounding rock of the tunnel is stable, and the displacement of the supporting structure is small, and the maximum displacement is about 20 mm, which is located at the vault. Therefore, the monitoring work should be done well and the support can be strengthened properly during the construction.

Reconstitution method for tunnel spatiotemporal deformation based on 3D laser scanning technology and corresponding instability warning

The three dimensional deformation and corresponding temporal evolution of surrounding rock is a key information for tunnel stability analysis and safety warning. To reconstruct the 3D deformation process of tunnel based on point cloud data by laser scanning, a semi-automatic method is presented to align the point cloud data of the tunnel surfaces at different stages. This method includes three steps: (i) initial alignment, splitting, denosing and merging of the tunnel surface’s point clouds; (ii) coordinate transformation between the tunnel surface’s point clouds according to the arch’s geometric characteristics; and (iii) calculation and visualization of the tunnel surface’s sequential deformation based on the multiscale model cloud comparison algorithm. The technical application of the time-dependent deformation analysis for an experimental tunnel in a mine indicated that this method can not only fully expose the evolution process of tunnel surrounding rock deformation, i.e., the spatial inhomogeneity, partitioning and temporal characteristics, but also can warn instability of tunnel by discerning hot deformation islands, i.e., zones with relatively large deformation.

Three-dimensional face stability analysis of shallow tunnels using numerical limit analysis and material point method

In this work, the collapse conditions of shallow tunnel faces are studied using the Numerical Limit Analysis (NLA) and the Material Point Method (MPM). A particular form (based on a mixed representation of velocities and stresses) of the lower bound formulation of numerical limit analysis was used. The solution using NLA is evaluated considering finite elements for the volume discretization in conjunction with the second order cone and semidefinite programming methodologies. Drucker-Prager and Mohr-Coulomb failure criteria have been used. In the case of MPM, the continuum media is discretized by a set of material points which store all the relevant properties and variables such as mass, stress, velocity, and energy. The objective of this paper is to evaluate the characteristics of both methods when applied to the determination of the tunnel face stability conditions of shallow tunnels, in particular to the determination of failure mechanisms and run-out analysis of the failed mass. Results obtained from experiments on a small-scale model (Sterpi et al., 1996) are used as a reference for the study. The results obtained showed that both MPM and NLA can predict the global failure mechanism and the minimum tunnel face pressure required for stability.

Construction Method and Stability Analysis of High-speed Rail Tunnel Crossing Fault Broken Zone

Construction Method and Stability Analysis of High-speed Rail Tunnel Crossing Fault Broken Zone

Face Stability Analysis of EPB Shield Tunnels in Dry Granular Soils Considering Nonuniform Chamber Pressure and a Dynamic Excavation Process

Abstract The support pressure at the tunnel face of earth pressure balance (EPB) shield machines is usually assumed to be uniform from the crown to the invert, which is a notable simplification of ...

Undrained stability analysis of dual unlined horseshoe-shaped tunnels in non-homogeneous clays using lower bound limit analysis method

A rigorous adaptive lower bound limit analysis method with 3-noded element (LB-FELA) is adopted to discuss the tunnel stability and failure mechanism of dual unlined horseshoe-shaped tunnels in non-homogeneous clays. The clays mass has heterogeneity, where the shear strength increases linearly with depth. This problem is defined as a plane strain analysis model. The calculation results are provided using the dimensionless stability numbers, which are affected by dimensionless parameters C/D, S/D and ρD/c0.The typical failure mechanisms of the dual horseshoe-shaped tunnels are presented based on the parametric studies using the final refined meshes of the proposed method. The results show that the dimensionless parameters ρD/c0, C/D,and S/D have great influences on tunnel stability and failure mechanism of the dual horseshoe-shaped tunnels. Using the calculation results provided by this paper, the tunnel designers can directly evaluate the stability of the tunnel in non-homogeneous clays.

Three-Dimensional Face Stability of Tunnels in Unsaturated Soils with Nonlinear Soil Strength

Stability analysis of tunnel faces is usually carried out under dry or saturated assumptions. However, in practice, soils are often unsaturated due to the presence of matric suction, and unsaturated components often have nonnegligible effect on soil strength. For a more realistic solution, the influence of unsaturated components on the stability of a three-dimensional tunnel face was considered for the first time. To meet this requirement, the three-dimensional rotational failure mechanism and the extended form of Mohr–Coulomb failure criterion were used to express the face failure in the limit analysis framework. The strength reduction technique was employed to estimate the stability of ta hree-dimensional tunnel face and the safety factors were calculated by the bracketing method. The proposed method is verified by comparing with the results obtained by FLAC3D. The effects of matric suction distribution, tunnel geometry parameters and shear strength nonlinearity on the stability of three-dimensional tunnel face were analyzed in the parameter analysis. The results show that considering the effect of suction stress is beneficial for improving the tunnel face stability, but it is influenced by the matric suction distribution, the tunnel geometry, soil types, and the shear strength nonlinearity. The main novelty of this study is to develop an effective method to evaluate the face stability of tunnels in unsaturated soils.

Creep Parameter Inversion and Long‐Term Stability Analysis of Tunnel Based on GP‐DE Intelligent Algorithm

Aiming at the creep problem of Banshi Tunnel in Jilin province, the creep laws of rock are analyzed by the creep test, and the Cvsic model describing the creep characteristics of the tunnel is established. To obtain the creep parameters accurately, considering the advantages of Gauss process and differential evolution algorithm, coupling the two methods, a Gauss process‐differential evolution intelligent inversion method is proposed. According to on‐site monitoring data, the the creep parameters of the tunnel are accurately inverted. On this basis, the stability analysis of the tunnel and the selection of a reasonable construction plan are carried out. The research results show that to ensure the stability of the tunnel, the construction scheme of initial lining + pipe shed + advanced grouting anchor rod should be adopted. The research results have guiding significance for the long‐term stability evaluation of the tunnel.