Tunnel Failure Research Articles

Research on Meso-mechanism of Failure Mode of Tunnel in Jointed Rock Mass

The natural rock that contains micro particles, holes, cracks, impurities, etc. has a complex composition. According to whether the crack is closed or not, kinds of cracks can be divided into two types: open type and closed type. There was a bottleneck in the preparation of the test piece when the indoor test method analyzes the built-in closed cracks of rock materials, so PFC has its unique advantages in simulation analysis of fractured rocks with closed cracks. In order to analyze the influence of the inclination angle, length of the crack above the tunnel and the tunnel spacing on the tunnel failure and crack propagation, the particle was based on the granular flow microscopic parameters. It was shown that with the increase of the inclination of the pre-crack on the upper side of the tunnel, the distance of the tunnel and the length of the crack, the final failure mode of the specimen is similar to that of the non-crack specimen. The initiation of the crack at the end of a certain length of prefabricated crack is mainly affected by its inclination angle. The greater the inclination angle, the earlier the crack initiation is relatively early.

Support Measures to Prevent the Deformation and Failure of a Carbonaceous Mudstone Tunnel

A carbonaceous mudstone tunnel is a type of soft rock tunnel. There is little research on the prevention and control measures for the deformation and failure of carbonaceous mudstone tunnels. In this article, we investigated the construction of the Qiguding carbonaceous mudstone tunnel in Meizhou City, Guangdong Province, China. We monitored and analyzed the deformation and stress characteristics of a section under the original support scheme. The monitoring data showed that this section had large peripheral convergence, vault subsidence, steel arch strain, and concrete strain. The deformations exhibited significant differences in the horizontal and vertical directions, eventually resulting in concrete cracking, steel arch bulging, and distortion in the section. The analysis showed that the primary mechanisms for the failure were the softening characteristics of the carbonaceous mudstone, the plastic rheology, and the shear slip of the rock stratum. Based on a comparative analysis and numerical simulation, we proposed a new support measure called the longitudinal rigid enlarged foundation that consists of a steel arch longitudinal connection system and a locking foot anchor pipe system. Several comparative tests were performed at the tunnel site. The results demonstrated the excellent performance and reliability of the proposed support scheme for the deformation control of the carbonaceous mudstone, providing a reference for similar projects.

An Analysis of Loess Tunnel Failure and Its Mechanism

A series of changes of mechanical properties such as fracture development, relaxation, collapse deformation, and strength decreasing of the surrounding rock of loess tunnels occur due to shearing and immersing, and loess tunnels will be prone to engineering failures, including large deformation, fissure, ground collapse, landslide, and lining cracking, seriously threatening the construction and operation safety of tunnels. These problems are especially prominent for long-span loess tunnels. Based on the understanding of features in the construction and operation of the loess tunnel project and proceeding from the perspective of structural evolution of loess, distribution of the shear deformation zone, instability of the excavation face, and adverse effects of geological conditions, the predisposing factors of damage of the surrounding rock and the supporting structure of large-span loess tunnels, common types of failures, and their formation mechanisms are analyzed in this paper. According to the relationship between the evolution of the loess structure and the law of strength change, an improved Mohr–Coulomb elastic-plastic, tension-compression-shear, constitutive model, considering the loess structural property, is established and applied in numerical calculation. The formation mechanism of different failures in the course of loess tunnel construction is revealed by numerical analysis, in which the structural property of loess, loess strata, geological conditions, and excavating and supporting actions are simulated by the numerical method. A reference is provided for the prevention and remediation of engineering failures of a loess tunnel.

Revised Comparison of Tunnel Collapse Frequencies and Tunnel Failure Probabilities

Comparison of calculated failure probabilities of technical systems with observed failure frequencies is an important part of the assessment of probabilistic calculations and can point to significant factors that are neglected in the calculations. Recent comparisons of failure probabilities and failure frequencies of nuclear power plants, bridges, and dams have shown that the calculated and observed values correspond surprisingly well. In addition, although various factors could be identified which have both positive and negative influences on the observed values, they almost cancel each other out. This study focuses on the comparison as it relates to tunnels. Extensive statistics indicate that most tunnel collapses occur during construction. Although this is also seen to a certain extent in bridges, it is not to the extent seen in tunnels. Events such as earthquakes and floods, which are the major causes of collapse of other structures, account for only about 10% to 20% of all tunnel collapses. Increasingly, tunnels are also being proven probabilistically. Based on these calculations, the available failure statistics can be compared with representative probabilistic tunnel proofs. The comparison shows large deviations between individual computations as well as between the mean value of all computations and the observed collapse frequencies.

Analysis of Surrounding Rock Creep Effect on the Long‐Term Stability of Tunnel Secondary Lining

The secondary lining failure of deep buried soft rock tunnel often occurs, which is obviously related to the time factor. The formation mechanism of this phenomenon is studied in this paper. Therefore, the combination of in situ stress measurement and neural network inversion is used to analyze the distribution characteristics of in situ stress. At the same time, the creep characteristics of surrounding rock are tested in laboratory, and the key parameters are obtained. Combined with the characteristics of surrounding rock, the calculation model is established by using discrete element simulation technology and considering the joints of surrounding rock. According to the above multiple information, the stress characteristics of the secondary lining in different time periods are analyzed creatively. Finally, the method of setting arch and adding anchor bolt in key parts is proposed, and significant effect results are obtained.

Experimental Investigation of Spalling Failure of D-Shaped Tunnel Under Three-Dimensional High-Stress Conditions in Hard Rock

The D-shaped cross section is a commonly used tunnel cross section in underground engineering. To simulate the failure process of a D-shaped hole under deep three-dimensional (3D) high-stress conditions, true-triaxial tests were conducted on cubic granite specimens with a through D-shaped hole, and the failure process of the hole sidewall was recorded in real time. Results show that the spalling failure process of the D-shaped hole sidewall can be divided into four periods: calm, fine particle ejection, crack generation and propagation, and rock slab gradually buckling and spalling. Afterwards, symmetrical V-shaped notches were formed on both sidewalls between the corner and arch springing. The spalling failure shows tensile failure characteristics. Under high vertical stress and constant horizontal axial stress, increasing the lateral stress reduces the severity of the spalling failure and the depth of the V-shaped notch. The initial failure vertical stress of the D-shaped hole sidewall is higher than that of circular hole sidewall, and the failure of D-shaped hole sidewall is mainly characterized by static failure. The failure of the circular hole sidewall is a more severe dynamic failure. When the vertical applied stress is the maximum principal stress, the position of the V-shaped notch tip is 0.20–0.25 h (h is the height of the D-shaped tunnel) from the tunnel floor, whereas that in the circular tunnel is 0.5 d (d is the diameter of the circular tunnel) from the tunnel floor. Specific support schemes should therefore be designed for tunnels with different cross sections according to the damage location, depth of failure zone, and severity of failure.

Study on Mechanical Failure and PermeabilityCharacteristicsof Porous Gas-Bearing Coal under Triaxial Stress

To explore the mechanical failure and permeability characteristics of porous gas-bearing coal under triaxial stress, the triaxial compression experiment was carried out for porous and conventional gas-bearing coal samples based on the triaxial creep-seepage experiment system and sound emission signal acquisition system. Acoustic emission testing was carried out at the same time of loading failure. The experimental results showed that (1) under fixed gas pressure but changing confining pressure, the porous gas-bearing coal sample had higher peak strength and elastic modulus but lower peak strain; under changing gas pressure but fixed confining pressure, the porous gas-bearing coal sample had lower peak strength and peak strain but higher elastic modulus. When either confining pressure or gas pressure was changed, the mechanical properties of the two kinds of gas-bearing coal samples showed a good consistency, but the mechanical parameters differed greatly, with the peak strength, peak strain, and elastic modulus of porous coal samples are reduced by 1/4, 2/3, and 3/4, respectively. (2) When either the confining pressure or gas pressure was changed, the permeability of the porous gas-bearing coal sample was larger than that of the conventional gas-bearing coal sample. However, the change rules of permeability characteristics of the two were basically the same, except that there was a large difference in permeability value that the porous gas-bearing coal sample increases nearly twice as much as that of the conventional gas-bearing coal sample. (3) In the whole stress-strain process, the acoustic emission characteristics of the porous gas-bearing coal sample differed significantly from those of the conventional gas-bearing coal sample. The maximum ringdown count of the porous gas-bearing coal sample can be reduced by one-third at most, the maximum energy can be reduced by nearly half at most, and the maximum amplitude changes little with only 1–3 dB reduction. The research results have important guiding significance for the prediction of failure and instability of coal tunnel and the development of relevant protective techniques.

Anisotropic Failure in Foliated Rock Tunnels: Comparison between Deformational Behavior and Confined Pressure

Foliated rock mass, such as slate, schist, and phyllite, is widely distributed in Northwest China. During tunnel excavation, some geotechnical problems are encountered in the surrounding rock, such as excessive over break and intense deformation by asymmetric squeezing, because of low strength, poor self-stationary, and intense anisotropy of structural strength. The large deformation results in intense damage of the primary support and splitting of the secondary support, which can significantly influence the construction and security of tunnels. Anisotropic failure in foliated rock tunnels under high stress conditions has become an engineering challenge. The deformational anisotropy of both rock and underground structures has drawn increasing attention in the field. The relative orientation of foliation plays an essential role on the deformational behavior of layered surrounding rocks by laboratory experiments and numerical simulations. Meanwhile, the symmetrical rigid support structure cannot effectively resist the asymmetric deformation exhibited by the excavation in foliated rock mass. Consequently, the excessive confined pressure generated between surrounding rock and support is essential for anisotropic failure in tunnels. In-situ monitoring tests of deformation and contact pressure were conducted in different positions of sections within a deep-buried tunnel in the Lanzhou–Chongqing railway. The comparison results indicated that the contact pressure of the support system showed irregular space distribution, which agreed with the concentrated deformation position of the surrounding rock. However, the monitoring data showed that the occurrence of failure obviously lagged behind the stabilization of convergence deformation. The internal confined pressure could last for a long time period than the deformation monitored outside. The failure of the support takes place in the weak axis plane because of its small lateral anti-bending rigidity. The authors believe that the proposed findings will be a step further in supporting the design of tunnels passing through foliated rock mass under high in-situ stress conditions.

Tunnel failure in hard rock with multiple weak planes due to excavation unloading of in-situ stress

Natural geological structures in rock (e.g., joints, weakness planes, defects) play a vital role in the stability of tunnels and underground operations during construction. We investigated the failure characteristics of a deep circular tunnel in a rock mass with multiple weakness planes using a 2D combined finite element method/discrete element method (FEM/DEM). Conventional triaxial compression tests were performed on typical hard rock (marble) specimens under a range of confinement stress conditions to validate the rationale and accuracy of the proposed numerical approach. Parametric analysis was subsequently conducted to investigate the influence of inclination angle, and length on the crack propagation behavior, failure mode, energy evolution, and displacement distribution of the surrounding rock. The results show that the inclination angle strongly affects tunnel stability, and the failure intensity and damage range increase with increasing inclination angle and then decrease. The dynamic disasters are more likely with increasing weak plane length. Shearing and sliding along multiple weak planes are also consistently accompanied by kinetic energy fluctuations and surges after unloading, which implies a potentially violent dynamic response around a deeply-buried tunnel. Interactions between slabbing and shearing near the excavation boundaries are also discussed. The results presented here provide important insight into deep tunnel failure in hard rock influenced by both unloading disturbance and tectonic activation.

Long-term deformation and control structure of rheological tunnels based on numerical simulation and on-site monitoring

The time-varying and creep failure of rocks affect the long-term stability of support structures in deep rheological tunnels. Structure instability is the macroscopic result of damage evolution and strength degradation in microstructures. Hence, the calculation model of long-term deformation and failure of soft rock tunnels is established. The model explains the heterogeneity of rocks by a random local stress field, and explains the local degradation of rocks by an exponential softening law. The effect of stress field distribution on failure mode and long-term instability is revealed. The deformation characteristics of different structure sections are analyzed, and the damage evolution process, failure, and instability properties are further clarified in rock tunnels. The results indicate that the coefficient of lateral pressure determines the long-term creep and damage properties of the surrounding rock, and the rocks show a strong time effect from a large to small deformation rate. The stability of curve shapes is better than that of straight ones in deep tunnels. The shoulder and foot of the structure are always damaged firstly, and continue to evolve in an arc until fracture. A mechanical mechanism is applied to the design of a stable structure, and the control principle of soft rocks is proposed: stress–deformation applicability and space–time applicability. The failure mechanism, control principle, and stability structure “yielding bolt + W steel strip + shotcrete” are demonstrated with the soft rock tunnels of cross mining in Baijiao Coal Mine. Finally, results of this study promote the utilization of soft rock tunnels and provide a new control structure for engineering stability in deep-cross mining.

Effect of particle shape on the progressive failure of shield tunnel face in granular soils by coupled FDM-DEM method

The face failure of tunnels has been extensively studied. However, the effect of particle shape on the failure process still remains unclear. In this paper, the progressive face failure of a shield tunnel in sand is analyzed with coupled discrete element method (DEM) and the finite difference method (FDM) in three-dimension. Soils at the tunnel face, where large deformation occurs and continuum mechanics description does not apply, are modeled with DEM. And the FDM is used for the rest areas where deformation and displacement are relatively small. In order to obtain appropriate parameters for soils as reference, a series of triaxial tests on both loose and dense soils are conducted. The face failure is generated by moving the tunnel forward and backward, which, respectively, simulates the collapse failure corresponding to the tunneling speed higher than soil excavating speed and the blow-out failure corresponding to the converse case. In particular, the effect of particle shape on the failure process is investigated in detail by adopting tetrahedral particles, elongated particles and spherical particles with rolling resistance coefficient of 0.0, 0.1, 0.2 and 0.4. The soil movement, ground surface movement, supporting force of the tunnel face, and the distribution of microscopic contacts are analyzed during the progressive failure of the tunnel face, which demonstrate a significant effect of particle shape.

Upper bound analysis of collapse failure of deep tunnel under karst cave considering seismic force

When tunnels are excavated in karst areas, the existence of karst caves in the surrounding rock usually results in the collapse failure of tunnels. Tunnel collapse has always been a challenging issue because it seriously threatens the safety of tunnel builders. To investigate the collapse of a deep tunnel under a karst cave, we constructed the collapse mechanisms of the rectangular and circular tunnels under a karst cave, and obtained the expressions of the collapse failure in tunnel considering seismic force and seepage force by means of the variational principle and limit analysis theory. Compared with previous results and numerical solutions, it is found that the results in this paper are consistent with those results and numerical solutions, which indicates that the proposed method in this work is rational. According to the analytical solutions, the shape of the collapsing blocks of the deep rectangular and circular tunnels under a karst cave are drawn, and the effects of different parameters, especially the vertical seismic coefficient kv, on the collapsing blocks are analyzed. The findings in this paper indicate that the range of collapsing blocks decreases with increased kv. The two formulas for calculating the critical height between the tunnel and the karst cave are given by derivation.

Assessment of the Stability of an Unlined Rectangular Tunnel with an Overload on the Ground Surface

City tunnels are often constructed at shallow depths, and tunnel failure may be initiated by overloads resulting from surrounding buildings, structures, heavy‐haul trailers, and other installations. Although several works have been reported on tunnel stability, stability numbers have mainly been obtained for cases with fully cohesive soils. Moreover, little information has been presented about the influence of overloads on the failure patterns for unlined rectangular tunnels. This paper uses upper‐bound finite element methods to assess the stability of an unlined rectangular tunnel in cohesive‐frictional soils with an overload acting on the ground surface. A complete set of dimensionless parameters covering the tunnel size and shallow tunnel depth and Mohr‐Coulomb material parameters are determined to obtain the dimensionless overload. In addition, failure modes that are similar to slip line fields are acquired. A failure mechanism that may cause base heave is proposed in this paper to improve the accuracy of the results. These failure patterns are more complex for cases with larger dimensionless depth, larger internal friction angle, and smaller dimensionless unit weight. Compared with the rigid‐block mechanisms from the upper‐bound rigid‐block analysis method, these computed failure mechanisms are better suited for rectangular tunnel stability analysis.

Risk identification in tunnel construction project: A literature review

Every construction project is always faced with the possibility of various occurrence kinds of risks. The higher the level of complexity of a project, the greater the level of risk that might happen to the project. Based on historical data from tunnel construction many problems and even failure of tunnel construction caused by various factors has been noted and it can have an impact on project delays. A risk management is expected to reduce the adverse impact of risks faced during construction work. Tunnel construction needs management handling with high risk, so it is necessary to identify risks that can minimize bad risks. A risk management is expected to reduce the adverse effects of risks faced in a construction work. It is necessary to perform risk identification to manage the risks that we will face. To successfully improve the performance of tunnel projects, we need to identify various risk factors in a project for efficient project fulfillment. The research method begins with an extensive literature review by reviewing at least 48 journal, journal papers, review articles to provide a list of the main risk factors which are also added to the expertise to achieve a list of final risk factors that contain all risks that may be encountered during road construction. This analysis involves the identification, classification of various risks involved in the construction of a tunnel construction project.

Application of stochastic joint network simulation to composite strata of shallow-buried long-span metro tunnels

A large number of shallow-buried tunnels have currently been built in cities, and specific strata, such as thick upper-soft and lower-hard ground layers, are often encountered. For shallow-buried large-span metro tunnels in urban composite strata, it is particularly important to study the effects of rock mass structures on engineering applications; random joint network simulation technology is a suitable method to study this problem. Considering the shallow-buried large-span metro tunnel in Dalian, which is located in a composite stratum, as the engineering background, first, a set of visualizations is developed with a joint network simulation program. The program can also generate several sets of joints and multistratum random joint networks and then combine program-generated data files and UDEC discrete element software-generated random network models. Combined with orthogonal testing, the failure modes of shallow-buried large-span metro tunnels are discussed, and the influences of rock mass structural parameters on tunnel failures are analyzed. The results indicate that the failure modes of all models are shear or tension failure of the overburden strata along weak planes of random joints, which eventually leads to the occurrence of staggered traction slip collapses and clear slip surfaces. This study provides a certain degree of guidance for the deformation and failure of shallow-buried large-span metro tunnels and for the determination of the surrounding rock pressure in urban composite strata.

Effect of Voids Behind Lining on the Failure Behavior of Symmetrical Double-Arch Tunnels

The presence of voids behind lining seriously affects the safety of the symmetrical double-arch tunnels during service life. It is essential to find out the impact of voids on tunnel safety due to the increasing demand for the construction and maintenance of symmetrical double-arch tunnels. Model tests and numerical analyses were conducted in this research. The results attained were explored including earth pressure, internal force, and lining failure. Results reveal that the presence of voids has a large influence on the internal force in the lining of symmetrical double-arch tunnels, generally in the form of asymmetrical failure patterns of the lining. The failure patterns of the lining are greatly influenced by the size and location of voids with respect to the symmetrical double-arch tunnel circumference. Significant changes in the lining internal forces were found at the areas in the close vicinity of the void whereas a few changes were found at the bottom of the sidewall, the invert, and the central wall far away from the void. The propagation laws of lining cracks of asymmetrical double-arch tunnels are more complicated than symmetrical tunnels with a void behind the central wall. The location of the initial cracking of symmetrical and asymmetrical double-arch tunnels is the same, while the lining failure of the large-section tunnel is the most complicated.

Experimental simulation and investigation of spalling failure of rectangular tunnel under different three-dimensional stress states

Spalling (or slabbing) in the sidewalls of deep rectangular tunnels is a type of rock failure phenomenon under the three-dimensional stress environment, which often occurs on the surrounding rocks after the tunnel face excavation is completed and has a significant impact on the safety of construction and support. In order to investigate the spalling process in deep rectangular excavated tunnels under three-dimensional stress, a granite material was firstly processed into cubic specimens (100 mm × 100 mm × 100 mm) with prefabricated rectangular holes (40 mm × 40 mm). Simulation experiments were performed using a rock true-triaxial electro-hydraulic servo mutagenesis testing system under four different initial stress states. Meanwhile, a wireless micro-camera was used to record and monitor the damage process on the sidewalls of the rectangular tunnel in real time. The results showed that under the four stress conditions, an evident spalling failure occurred on the entire sidewalls of the rectangular hole. It was observed that the spalling-damaged zone gradually developed toward the deep part of the hole in a horizontal direction. Finally, it formed a penetrating symmetric arc-shaped groove along the axial direction, whereas the roof and bottom slab remained stable. The spalling failure process of the sidewalls had four stages: the calm period, particle ejection at the upper and lower shoulders, sidewall crack propagation, and crack penetration spalling failure. Compared with the dynamic failure (rockburst) of a circular tunnel under the same three-dimensional high stress conditions, the spalling failure of the rectangular tunnel sidewalls was of the static failure mode. Under the three-dimensional stress condition, the radial stress had a greater effect on the spalling failure than the axial stress, by increasing the radial stress can be significantly reduced the degree of spalling failure and effectively improved the stability of the surroundings.

Stability Analysis of Surrounding Rock in Tunnel Crossing Water-Rich Fault Based on Catastrophe Theory

The failure of surrounding rock in tunnel crossing water-rich fault is a sudden damage phenomenon with obvious nonlinear and abrupt characteristics, which is characterized by the uncertainty of deformation, the nonlinearity of constitutive relation and the mutation of failure process. Based on the mechanical model of tunnel-fault system, the cusp catastrophe model of the failure of surrounding rock in tunnel crossing water-rich fault is established. Combining with the field monitoring data, the model is employed to judge the stability of surrounding rock. Results show that the deformation curve of tunnel vault has a good correlation to the cusp catastrophe model, and the results for stability analysis is consistent with the actual situation. The influences that the strength of rock mass, groundwater and fault width have on the failure of tunnel are further discussed, which provides scientific guidelines to the construction of tunnel.

Experimental evaluation of PMMA simulated tunnel stability under dynamic disturbance using digital image correlation

The dynamic disturbance is a non-ignorable external factor inducing rock mass instability around underground caverns. In this paper, the failure characteristics of the polymethylmethacrylate (PMMA) simulated tunnel under coupled biaxial static stress and high strain rate dynamic disturbance are experimentally investigated. The effects of lateral pressure coefficient, overbreak and underbreak, fault, and dynamic disturbance direction on the PMMA simulated tunnel failure are considered. During the tests, the two-dimensional digital image correlation (DIC) technique is used to monitor the failure process. The results indicate that the contribution of the dynamic disturbance on the failure of the PMMA simulated tunnel is closely related to the static in-situ stress. Sufficient static stress is essential for PMMA simulated tunnel failure under dynamic disturbance. The effect of the lateral pressure coefficient is not monotonic but depends on the relationship between horizontal and vertical in-situ stresses. For specimens with prefabricated defects, the cracks always initiate from the protruding defects with rough boundary. Thus, in areas where the tunnel is seriously under-excavated or over-excavated with rough boundary, attention should be taken to prevent and mitigate the severe damage caused by dynamic disturbances. The effect of the fault on the PMMA simulated tunnel stability depends on both the distance between the fault and the tunnel, and the dip of the fault. Most devastating failure occurred when the dynamic disturbance is applied in the direction of the higher static in-situ stress.

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.