Stability Analysis Of Tunnel Research Articles

Stability Analysis and Support Design of Imam Reza Tunnel in Ardabil Sarcham Road by Numerical Methods

Geological structures and performance of the geodynamic processes can affect engineering projects on their own. Hence, the stability analysis and designing methods for foreseeing the retaining and support system for tunnels are diverse and came from different points of view. So this study seeks to present stability analysis of Imam Reza tunnel in Ardabil Sarcham Road with a special focus on the impact of future earthquakes on its stability using numerical methods. In this study, first designing and operating the initial structure with the height of 5.5 m and a semi-circular cross section. Secondly, drilling with the height of 3m and the width of 7.34 m and with a rectangle cross section. For stabilization, Rock Mass Rating (RMR) geomechanical classification systems and methods used. At the stabilization level, the materials were examined in laboratory, regarding the properties of sides and roof of the tunnel and pressure on them. The results of physical and mechanical experiments shown that the compressive strength ranged from 400 kg/cm2 to 500 kg/cm2 on average. The elastic modulus is between 12 and 13 GPa for the rocks. The Cohesion (C) ranged from 4-5MPa to 5 MPa and the Angle of Internal Friction (φ) is between 60ᵒ and 50ᵒ.

Upper-bound stability analysis of dual unlined horseshoe-shaped tunnels subjected to gravity

This study investigates the stability of dual horseshoe-shaped tunnels in cohesive-frictional soils subjected to gravity using an upper-bound finite element method combined with a plastic-dissipation-based mesh adaptive strategy. The results are presented in the form of dimensionless stability numbers, which decrease with C/D and increase with ϕ. The results indicate that the interaction between dual horseshoe-shaped tunnels disappears when their dimensionless center-to-center distance S/D lies approximately in any of the following ranges for C/D: (i) 3.5–4.5 for C/D = 1, (ii) 3.5–6.5 for C/D = 2, (iii) 3.5–9 for C/D = 3, (iv) 4–11 for C/D = 4, and (v) 4–13.5 for C/D = 5.

Investigate the effect of rock mass joint intensity on performance of support systems in the tunnel by using DFN-DEM numerical modeling (Case study: the access tunnel of Rudbar Lorestan Dam plant)

Summary In this paper, a DFN-DEM simulation using PFC3D software has been carried out to evaluate the effect of joint intensity variation on tunnel support systems performance. The obtained results indicated more resistance of steel frame against change of rock mass fracture intensity in relation to shotcrete. Introduction The geometric properties of joint sets, especially joint intensity, may be changed by various factors such as explosion, earthquakes, faulting etc. Therefore, it is essential to study the performance of tunnel support systems under various conditions of joint intensities. In this paper, by focusing on the access tunnel to the gallery of Rudbar Lorestan dam as a real case study, simulation of tunnel support systems and its surrounding rock mass close to the real condition using the DFN-DEM approach and PFC3D software is provided. Also for the first time, the dependence of the performance of shotcrete and steel frame to change the intensity of fracturing of rock mass, at this level of accuracy in simulation of jointed rock mass, has been investigated. Three dimensional distinct element software, PFC3D is considered for numerical modeling in this paper. This software has many advantages such as ability to create three-dimensional distinct joints with limited size and with different statistical characteristics, flexibility in different conditions and ability to monitor a momentarily caving and falling during tunnel stability analysis. Methodology and Approaches In this paper, at the first stage, by using the discrete fracture network (DFN) modeling and based on the surveyed data from the access tunnel, existing fractures in this region have been simulated in the PFC3D software. Then the model is linked with the intact rock model. Finally, the performance of tunnel support systems of shotcrete and steel frame relative to changes of the rock mass fracture intensity is investigated. Results and Conclusions Serious damage to Shotcrete support system occurs by doubling the number of joints, while serious damage occurs in the steel frame by quadrupling the number of joints. Therefore, by increasing joint intensity due to various factors such as explosions, earthquakes etc., the steel frame support system has higher reliability.

Stability Analysis of Underground Tunnel for 2nd Perimeter Highway Construction Work in Incheon

Construction of underground tunnel for highway in the urban area is a challenge to overcome many problems such as subsidence of residential houses and commercial buildings, broken of utilities lines, and vibrating and noise due to rock blasting. This paper presents the analysis of stability of 5.6 km long underground tunnel both partially completed tunnel and planed tunnel section, and the cause of tunnel collapse due to sinkhole. Several methods applied to analyze the stability of tunnel by the monitoring the instrumented data; settlement of ground, ground water level, and lateral and vertical displacement of internal face of tunnel. Soil investigation was also conducted to identify the exact soil layer characteristics and strength of soil and rock, and stratification of soil ground. The rock core was obtained and evaluated for the specimens from the 50 m long horizontal pre-boring process. The numerical analysis was carried out for the stability of tunnel in terms of internal displacement of tunnel, shotcrete bending compressive stress, and rock bolt axial force. GPR survey was also conducted for detection of sinkhole along the route of underground highways.

Face stability analysis of shield-driven tunnels shallowly buried in dry sand using 1-g large-scale model tests

This paper investigates the face stability of shield-driven tunnels shallowly buried in dry sand using 1-g large-scale model tests. A half-circular tunnel model with a rigid front face was designed and tested. The ground movement was mobilized by pulling the tunnel face backwards at different speeds. The support pressure at tunnel face, settlement at ground surface, and internal movement of soil body were measured by load cells, linear variable differential transducers, and a camera, respectively, and the progress of face failure was observed through a transparent lateral wall of model tank. The tests show that, as the tunnel face moves backwards, the support pressure at the tunnel face drops sharply initially, then rebounds slightly, and tends to be stabilized at the end. Similarly, the ground surface settlement shows a three-stage variation pattern. Using the particle image velocimetry technique, the particle movement, shear strain, and vortex location of soil are analyzed. The variation of support pressure and ground surface settlement related to the internal movement of soil particles is discussed. The impact of the tunnel face moving speed on the face stability is discussed. As the tunnel face moves relatively fast, soil failure originates from a height above tunnel invert and an analytical model is developed to analyze such failure.

Probabilistic analysis of tunnels considering uncertainty in peak and post-peak strength parameters

Stability analysis of rock tunnels is a complex problem because of various types of uncertainties present in the rock mass properties and hence probabilistic approaches are used to systematically consider these uncertainties in the analysis. While the uncertainty in deformation modulus and peak strength parameters has been considered previously it has been observed that the uncertainty in post-peak strength parameters is generally neglected in earlier studies. Post-peak strength parameters are among the most important factors which significantly influence the plastic zone development and displacements around the tunnel and hence neglecting uncertainty in post-peak strength parameters is not appropriate. In the current study, a quantitative approach based on the Geological Strength Index (GSI) has been used to estimate the uncertainty in peak strength, residual strength and deformation parameters. Then the uncertainty in yield zone and displacement around the tunnel is estimated using Hong’s point estimate method coupled with finite element method. The approach was used to estimate the displacements around tunnels of different shapes in three case studies in average quality rock mass and the predicted displacements were compared with the in-situ measurements. A comparison is provided with the generally adopted conventional probabilistic approach in which uncertainty in peak strength parameters and deformation modulus is considered and rock mass is assumed as elastic-perfectly plastic. It was observed that predicted displacements were matching well with the measured displacements for all the tunnels by considering uncertainty in residual strength parameters while displacements were underestimated when the conventional approach was used. A parametric study was conducted to estimate the influence of Coefficient of Variation (COV) of different parameters on the plastic zone development and displacements of rock tunnel by selecting one of the case studies. It was observed that COV of yield zone depth and displacement was varying with the COV of the intact rock properties and thus influencing the probability of failure.

Stress and pressure fields around two wellbores in a poroelastic medium

The problem of two circular wellbores of different size in a poroelastic medium is considered in the present work. The constitutive behaviour of the poroelastic medium is assumed to comply with the classical Biot model for isotropic porous materials infiltrated by compressible fluid. The wellbores are assumed infinitely long and the fluid flow is taken stationary, thus making it possible to perform a plane strain analysis. Owing to the geometrical layout of the system, bipolar cylindrical coordinates have been adopted. Three different sets of BCs on the pressure field and on the fluid flux have been considered, founding the corresponding forms of the pressure field. Based on Helmholtz representation, a displacement potential has been introduced, and the corresponding stress field in the poroelastic medium has been assessed. However, such a solution does not satisfy the BCs at the edges of the wells. Then, an auxiliary stress function, which allows accomplishing the BCs, is introduced, leading to the complete solution of the problem. The cases of two coaxial wellbores (eccentric annulus), a single hole bored in a poroelastic half plane and two intersecting holes have been considered also. The proposed approach allows evaluating the pore pressure and the stress and strain fields in the system varying the amplitude of the wells and the physical parameters of the porous material. In particular, the evaluation of the peak values of the stress components around the circular boreholes plays a key role in a variety of engineering contexts, with particular reference to the stability analysis of wellbores and tunnels and failure of vascular vessels in biological tissues.

Seismic stability analysis of subsea tunnels under the effects of seepage and temperature

ABSTRACTThis study used the strength reduction method to analyze the seismic stability of a subsea tunnel under the effects of seepage and temperature. Excess pore water pressure within the rock mass was first eliminated by calculating the consolidation; then, an earthquake wave was applied to begin the dynamic and time-history analysis and to obtain the maximum horizontal displacement of the model boundary. Finally, a temperature field model was established for the thermal analysis of the structure. The temperature of each node of the structure was regarded as a form of outside load applied to the reduction model; both sides of the vertical horizontal displacement of the boundary nodes and gravity were used as inputs for the static analysis when the vertex horizontal displacement reached its maximum value. By continuously decreasing the shear strength parameters, the safety factor of the tunnel structure was determined. The results show that the plastic zone first appeared in a smaller range on both sides of the tunnel arch feet near the lining and vault of both sides. The safety factor decreased with increasing water depth and overburden layer thickness.

Upper-bound stability analysis of dual unlined elliptical tunnels in cohesive-frictional soils

This study investigates the stability of dual unlined elliptical tunnels in cohesive-frictional soils using upper-bound finite element methods with rigid translatory moving elements (UBFEM-RTME). Results are determined in terms of dimensionless stability numbers, which increase with ϕ and decrease with increasing B/D and C/D, and collapse mechanisms, which mainly include two wedge-shaped zones and a complete non-plastic wedge. The center-to-center distance S significantly affects the stability of dual tunnels, and the interaction between the elliptical tunnels tends to disappear when Sc lies within (i) 2.5D-4D for C/D=1, and (ii) 4D-11D for C/D=5. The results agree well with those in literature.

Stability analysis of shallow tunnels subjected to eccentric loads by a boundary element method

In this paper, stress behavior of shallow tunnels under simultaneous non-uniform surface traction and symmetric gravity loading was studied using a direct boundary element method (BEM). The existing full-plane elastostatic fundamental solutions to displacement and stress fields were used and implemented in a developed algorithm. The cross-section of the tunnel was considered in circular, square, and horseshoe shapes and the lateral coefficient of the domain was assumed as unit quantity. Double-node procedure of the BEM was applied at the corners to improve the model including sudden traction changes. The results showed that the method used was a powerful tool for modeling underground openings under various external as well as internal loads. Eccentric loads significantly influenced the stress pattern of the surrounding tunnel. The achievements can be practically used in completing and modifying regulations for stability investigation of shallow tunnels.

Elastic-Plastic Numerical Analysis of Tunnel Stability Based on the Closest Point Projection Method Considering the Effect of Water Pressure

To study the tunnel stability at various static water pressures and determine the mechanical properties and deformation behavior of surrounding rock, a modified effective stress formula was introduced into a numerical integration algorithm of elastic-plastic constitutive equation, that is, closest point projection method (CPPM). Taking the effects of water pressure and seepage into account, a CPPM-based formula was derived and a CPPM algorithm based on Drucker-Prager yield criterion considering the effect of pore water pressure was provided. On this basis, a CPPM-based elastic-plastic numerical analysis program considering pore water pressure was developed, which can be applied in the engineering of tunnels and other underground structures. The algorithm can accurately take the effects of groundwater on stability of surrounding rock mass into account and it can show the more pronounced effect of pore water pressure on stress, deformation, and the plastic zone in a tunnel. The stability of water flooding in Fusong tunnel was systematically analyzed using the developed program. The analysis results showed that the existence of groundwater seepage under tunnel construction will give rise to stress redistribution in the surrounding rock mass. Pore water pressure has a significant effect on the surrounding rock mass.

Face stability analysis of shallow underwater tunnels in fractured zones

When an underwater tunnel constructed via the mining method crosses a fault fracture zone, one of the most important issues to consider is ensuring the stability of its face. Several auxiliary techniques have been adopted in construction; however, the design parameters of these auxiliary measures are mainly determined by experience. In this study, a stability analysis model of the working face of an underwater tunnel constructed via mining method in a fractured zone was established by considering the effect of groundwater seepage force. Afterward, the corresponding formula was determined. By considering a pre-support pipe roof and an advanced grouting ring as a beam on the elastic foundation, the corresponding stability analysis model and computing method under pre-reinforced condition were built. In addition, an engineering example was analyzed. Results show that the stability coefficient of the tunnel face is only 0.77 without the pipe roof and advanced grouting. Meanwhile, the stability coefficient increases to 2.47 under pre-reinforced condition. This finding indicates that a tunnel must be reinforced in advance in a fractured zone to ensure safe construction. The influences of pre-reinforcement parameters (i.e., thickness, cohesion, and internal friction angle of the grouting circle) on the stability of the tunnel face are discussed at the end of the article.

Integration of three dimensional discontinuous deformation analysis (DDA) with binocular photogrammetry for stability analysis of tunnels in blocky rockmass

This paper demonstrates and evaluates an integrated system coupling 3-dimensional binocular photogrammetry and discontinuous deformation analysis (DDA) for stability analysis of tunnels in blocky rockmass. 3D DDA is an effective numerical method for discontinuous and large displacement problems. In stability analysis of rockmass, especially for tunnels, one of the primary bottlenecks in 3D DDA is generating discontinuous models. For tunnel constructions requiring small interval time for blasting, traditional geotechnical data collection approaches such as hand-mapping and geologic compass are always lacking in efficiency and accuracy. 3D photogrammetry is an economical and efficient method for collecting geometric features and surface data. An integrated system connecting geometrical data acquisition and discontinuous numerical analysis automatically, is valid for improving safety in tunnel construction. This system includes photogrammetry module, modeling module and analysis module. In the photogrammetry module, binocular photogrammetry devices and image reconstruction technique are implemented for geometric data of rockmass. Then location, dip direction and dip angle of joints as well as other geometric information of tunnels are input into the modeling module to generate 3-dimensional discontinuous models. The analysis module using 3-dimensional DDA to evaluate the stability of the surrounding rock in tunnels. The integrated system is implemented in an engineering instance, Suocaopo Tunnel in Guizhou, China.

Analysis of EDZ Development of Columnar Jointed Rock Mass in the Baihetan Diversion Tunnel

Due to the time dependency of the crack propagation, columnar jointed rock masses exhibit marked time-dependent behaviour. In this study, in situ measurements, scanning electron microscope (SEM), back-analysis method and numerical simulations are presented to study the time-dependent development of the excavation damaged zone (EDZ) around underground diversion tunnels in a columnar jointed rock mass. Through in situ measurements of crack propagation and EDZ development, their extent is seen to have increased over time, despite the fact that the advancing face has passed. Similar to creep behaviour, the time-dependent EDZ development curve also consists of three stages: a deceleration stage, a stabilization stage, and an acceleration stage. A corresponding constitutive model of columnar jointed rock mass considering time-dependent behaviour is proposed. The time-dependent degradation coefficient of the roughness coefficient and residual friction angle in the Barton–Bandis strength criterion are taken into account. An intelligent back-analysis method is adopted to obtain the unknown time-dependent degradation coefficients for the proposed constitutive model. The numerical modelling results are in good agreement with the measured EDZ. Not only that, the failure pattern simulated by this time-dependent constitutive model is consistent with that observed in the scanning electron microscope (SEM) and in situ observation, indicating that this model could accurately simulate the failure pattern and time-dependent EDZ development of columnar joints. Moreover, the effects of the support system provided and the in situ stress on the time-dependent coefficients are studied. Finally, the long-term stability analysis of diversion tunnels excavated in columnar jointed rock masses is performed.

Face stability analysis of shallow circular tunnels in cohesive–frictional soils

The face stability of a circular tunnel in cohesive–frictional soils was numerically and theoretically investigated. Three-dimensional (3D) numerical simulations were first performed to analyze the face stability of a circular tunnel with a series of tunnel diameter-to-depth ratios and soil properties. The limit support pressure on the tunnel face and the failure zone in front of the tunnel face were both obtained from the numerical simulations. A simple and feasible criterion was suggested to outline the boundary strip of the failure zone at collapse in displacement clouds under different conditions. Based on the numerical simulation results, a new 3D failure mechanism was proposed using the kinematic approach of limit analysis theory to determine the limit support pressure of the tunnel face. The new 3D failure mechanism was composed of four truncated cones on which a distributed force acts. Finally, the limit support pressures and failure zones obtained from the new failure mechanism and the numerical simulations were compared. In addition, comparisons between the results of this work and those of existing approaches were performed. Overall, the new failure mechanism is substantially more consistent with the shapes of the failure zones observed in numerical simulations and experimental tests than the existing multi-block failure mechanisms. The new failure mechanism is more effective and reasonable.

ANALYTICAL SOLUTION FOR CIRCULAR TUNNELS WITH ROCK BOLTS

Analytical expressions of stress, displacement, and plastic zone radius in circular tunnels with or without rock bolts are presented. Considering a circular tunnel in hydrostatic stress field, with elastic-brittle-plastic rock mass, a linear Mohr-Coulomb yield criterion, and a non-associated flow rule, a new elastoplastic analytical solution for unsupported circular tunnels was derived. Based on the homogenization method, considering the composite material of rock mass and rock bolts as a new homogeneous, isotropic, parameter-strengthened equivalent material, the bolt density parameter was defined to reflect the influence of a high density support pattern of rock bolts, thus an equivalent Young’s modulus, equivalent cohesion, and equivalent friction angle for supported circular tunnels can be derived. Then an analytical solution for circular tunnel with rock bolts can be derived based on the new elastoplastic analytical solution without rock bolts. Bolt support was shown to be effective in reducing plastic zone radius and displacement of circular tunnel by comparison with an unsupported tunnel, also comparative analysis was undertaken using existing results and numerical solutions; the solutions derived provide reference for circular tunnel stability analysis in underground engineering.

Application of ABAQUS in Surrounding Rock Stability Analysis of Shallow Large Cross-Section Tunnel

HuJiaDi tunnel construction of Dai Gong highway is troublesome, the surrounding-rock mass give priority to full to strong weathering basalt, surrounding rock integrity is poor, weak self-stability of surrounding rock, and tunnel is prone to collapse. In order to reduce disturbance, taking advantage of the ability of rock mass, excavation adopt the method of "more steps, short footage and strong support". The excavation method using three steps excavation, The excavation footage is about 1.2 ~ 1.5 m; The surrounding rock bolting system still produce a large deformation after completion of the first support construction, it shows that the adopted support intensity cannot guarantee the stability of the tunnel engineering. Using ABAQUS to simulate tunnel excavation support, optimizing the support parameters of the tunnel, conducting comparative analysis with Monitoring and Measuring and numerical simulation results, it shows that the displacement - time curves have a certain consistency in numerical simulation of ABAQUS and Monitoring and Measuring.

Stability analysis of unlined elliptical tunnel using finite element upper-bound method with rigid translatory moving elements

The stability of an unlined elliptical tunnel in cohesive-frictional soils is determined. The analysis has been performed with two methods: finite element upper-bound method with plastic deformation elements (UP-PDE) and finite element upper-bound method with rigid translatory moving elements (UP-RTME). UP-PDE has been used to study tunnel stability by many scholars. The UP-RTME in combination with a finite element approach and triangular rigid translator moving elements is presented in detail. In the proposed method, the node coordinates and velocities of rigid elements are treated as unknowns without considering the rotating freedom. A specific plane strain formulation is proposed using nonlinear programming, and the optimal slip lines are determined by automatically adjusting the velocity discontinuities. Solutions for the influence of a range of soil parameters, dimensionless depths C/D and dimensionless spans B/D on the stability numbers γD/c and collapse mechanisms are solved using this method. The γD/c values increase with ϕ and decrease with C/D and B/D. γD/c is less sensitive to C/D as ϕ increases. The collapse mechanisms of unlined elliptical tunnels comprising two groups of slip lines are also presented, and they explicitly reflect the relative movement of blocks. The results show that these two methods are in agreement with each other.

Stability Analysis of Tunnel - Slope Coupling Based on Genetic Algorithm

Subjects in tunnels, being constrained by terrain and routes, entrances and exits to tunnels, usually stay in the terrain with slopes. Thus, it is necessary to carry out stability analysis by treating the tunnel slope as an entity. In this study, based on the Janbu slices method, a model for the calculation of the stability of the original slope-tunnel-bank slope is established. The genetic algorithm is used to implement calculation variables, safety coefficient expression and fitness function design. The stability of the original slope-tunnel-bank slope under different conditions is calculated, after utilizing the secondary development function of the mathematical tool MATLAB for programming. We found that the bearing capacity of the original slopes is reduced as the tunnels are excavated and the safety coefficient is gradually decreased as loads of the embankment construction increased. After the embankment was constructed, the safety coefficient was 1.38, which is larger than the 1.3 value specified by China’s standards. Thus, the original slope-tunnel-bank slope would remain in a stable state.

Three-dimensional face stability analysis of pressurized tunnels driven in a multilayered purely frictional medium

This paper aims at presenting a three-dimensional (3D) failure mechanism for a circular tunnel driven under a compressed air shield in the case of a dry multilayered purely frictional soil. This mechanism is an extension of the limit analysis rotational failure mechanism developed by Mollon et al. (2011a) in the case of a single frictional layer. The results of the present mechanism are compared (in terms of the critical collapse pressure and the corresponding shape of the collapse mechanism) with those of a numerical model based on Midas-GTS software. Both models were found to be in good agreement. Furthermore, the proposed mechanism has the significant advantage of reduced computation time when compared to the numerical model. Thus, it can be used in practice (for preliminary design studies) in the case of a multilayered soil medium.