Behavior Of Tunnel Lining Research Articles

Experimental investigation on damage development and failure mechanism of shield tunnel lining under internal blast considering stratum-structure interaction

With the expansion of international terrorism and the potential threat of attacks against civil infrastructure, the dynamic response and failure modes of underground tunnels under explosive loads have become a prominent research topic. The high cost and inherent danger associated with explosion experiments have limited current research on tunnel internal explosions, particularly in the context of scaled model tests of shield tunnels. This study presents a series of scaled model tests under 1 g-condition simulating internal blast events within a shield tunnel based on the prototype of the Shantou Bay Tunnel, considering the influences of surrounding stratum and equivalent explosive yield. Three different TNT explosive yields are considered in the model tests, namely 0.2, 0.4, and 1.0 kg. The model tests focus on the damage behavior and collapse modes of the shield tunnel lining under internal explosive loads. The model tests reveal that the shield tunnel is prone to damage at the joints of the tunnel crown and shoulder when subjected to internal explosive loads, with the upper half of the tunnel lining experiencing segment collapse, while the lower half remains largely undamaged. As the TNT equivalent increases, the damage area at the tunnel joints expands, and the number of segment failures in the upper half of the tunnel rises, transitioning from a damaged state to a collapsed state. The influence of “stratum-structure” interaction is investigated by comparing two models, one with overburden soil and the other positioned at the ground surface. The model tests reveal that the presence of soil pressure and confinement can significantly enhance the tunnel resistance to internal blast loads. Based on the observation of the model tests, five different damage modes of segment joints under internal explosion are proposed in this study.

A deep learning informed-mesoscale cohesive numerical model for investigating the mechanical behavior of shield tunnels with crack damage

The present deep learning (DL)-based detection of crack damage of shield tunnels through images can only provide part of geometric information of the crack damage, which prevents the comprehensive understanding of the mechanical behavior of the cracked tunnel linings. This study bridges the gap between the geometric information identified by DL models and the transformation law of mechanical behavior of tunnel linings revealed by numerical methods. A mask-region-based hybrid attention convolutional neural network (Mask R-HACNN) and mesoscale cohesive numerical model are developed to obtain the geometric information of crack damage and investigate the structural response of segments and joints with crack damage, respectively. The numerical simulation results demonstrate that the relationship between in-depth crack length and crack opening displacement and the relationship between the degradation stiffness and in-depth crack length are independent of the loading path. Based on these findings, prediction formulas are established to interpret the relationships between the stiffness degradation coefficients, flexural stiffness, in-depth crack length, joint openings, and crack opening displacement. Then, the geometric information of crack damage obtained by the Mask R-HACNN is provided to the mesoscale cohesive numerical model to estimate the in-depth crack length, flexural stiffness, and stiffness degradation coefficient of cracked segments. Results show that the deep learning informed-mesoscale cohesive numerical model is satisfying in understanding the mechanical behavior of segments and joints during crack damage evolution.

Multifidelity operator learning for predicting displacement fields of tunnel linings under external loads

In practical tunnel projects, the deformation of tunnel linings affects the service performance and structural reliability of tunnels. However, currently, several monitoring points must be installed to represent the specific deformation patterns of tunnel linings accurately, incurring high labor and financial costs. In recent years, the rapid development of artificial intelligence has provided potential solutions to this issue. To solve the aforementioned problem, this study proposed a multifidelity DeepONet framework, which comprised two neural networks. The first low-fidelity network was trained with data provided by a macro-level numerical model validated by experimental campaigns to learn the physical deformation patterns of tunnel linings. The second network was trained with limited high-fidelity monitoring data to learn the correlations between observations and numerical models. Even with very limited monitoring data, the proposed framework could still predict the mechanical behavior of tunnel linings under different loading scenarios. In this study, data collected from noncircular tunnel projects were used as case studies. The results demonstrated that the final output conformed to the deformation pattern obtained with the numerical simulations and was consistent with the actual measurements, achieving seamless fusion of the experimental campaigns and numerical models.

Evaluation of environmental and economic compatibility of different types of segment linings based on the structural performance with some aggravating factors

The performance of supporting systems can be significantly affected by aggravating factors that contribute to segmental tunnel lining damage. Based on previous studies and statistical data, the excessive thrust force and defect in support conditions are the crucial factors that can aggravate the damage of segmental linings during the installation stage. This study aims to evaluate the effect of influential factors, including the excessive thrust force, the incomplete contact of loading shoes, configuration of loading shoes, defect gap thickness, and segment type. In addition, a series of numerical simulation are performed to investigate the impact of the influential factors on the performance of three different segmental lining types, including conventional reinforced concrete segment, recycled steel fiber reinforced concrete segment, and new hybrid design recycled steel fiber reinforced concrete segment. The results indicated that numerical modeling can accurately simulate stress concentration and damage patterns of segmental lining in different conditions. This method can provide useful information about the performance of segmental tunnel linings, considering essential phenomena that are neglected in traditional design methods, such as the effect of incomplete contact of the support area, and the thickness of circumferential gap. Numerical analysis of segmental tunnel lining behavior by considering different conditions can help reduce undesirable consequences and construction costs. The results indicated that the increase in the thickness of the gap significantly increase in crack opening and destructive damages. While, the configuration of the loading shoes affects the amount of crack openings, the number and position of these cracks; the effect of this parameter is very lower compared to the presence of defects in the supporting area. Finally, it was concluded that the hybrid design showed high efficiency for all investigated conditions, in terms of structural performance, environmental impact and economic compatibility.

Investigation on the fire spalling behavior of underground structures in varied situations by global–local phase field modeling

The fire response of concrete underground structures and the near vicinity is not well understood yet, partly due to a lack of an effective and efficient fracture model for spalling of concrete, especially when the large-scale stratum-structure model is involved. In this paper, the spalling behavior is numerically reproduced by a global–local phase field method in light of the s-version finite element method. Only the mesh for the potential spalling zone is refined, which contributes to lowering the computational effort. Numerical models for different cases were constructed and studied to account for several influential factors, including the shape, size, buried depth of the tunnel, the fire scenario, and the ground conditions. These models were expected to show the fire-induced spalling behavior of tunnel linings and the induced disturbance to the nearby ground in varied situations. The comparative analysis indicates that the fire-induced spalling pattern on the tunnel lining is highly related to the fire scenario and the structural shape. Severe damage occurs at the position where there exists a high temperature gradient or concentrated stress. The heated surface of the vault/roof experiences settlement after a transitory upheaval, while the ground above the tunnel is constantly uplifted. The disturbance the ground suffered from the fire accident is relatively slight.

A simulation-based software to support the real-time operational parameters selection of tunnel boring machines

With the fact that the main operational parameters of the construction process in mechanized tunneling are currently selected based on monitoring data and engineering experience without exploiting the advantages of computer methods, the focus of this work is to develop a simulation-based real-time assistant system to support the selection of operational parameters. The choice of an appropriate set of these parameters (i.e., the face support pressure, the grouting pressure, and the advance speed) during the operation of tunnel boring machines (TBM) is determined by evaluating different tunneling-induced soil-structure interactions such as the surface settlement, the associated risks on existing structures and the tunnel lining behavior. To evaluate soil-structure behavior, an advanced process-oriented numerical simulation model based on the finite cell method is utilized. To enable the real-time prediction capability of the simulation model for a practical application during the advancement of TBMs, surrogate models based on the Proper Orthogonal Decomposition and Radial Basis Functions (POD-RBF) are adopted. The proposed approach is demonstrated through several synthetic numerical examples inspired by the data of real tunnel projects. The developed methods are integrated into a user-friendly application called SMART to serve as a support platform for tunnel engineers at construction sites. Corresponding to each user adjustment of the input parameters, i.e., each TBM driving scenario, approximately two million outputs of soil-structure interactions are quickly predicted and visualized in seconds, which can provide the site engineers with a rough estimation of the impacts of the chosen scenario on structural responses of the tunnel and above ground structures.

3D numerical study of the joint dislocation and spacing impacts on the damage of tunnel segmental linings

Aggravating factors of the segmental tunnel lining damage can severely affect the performance of support systems. Based on previous studies and statistical data, the excessive thrust force, offset, and gap are the essential factors that can aggravate the damage of segmental linings during the thrust force application stage. This study aims to evaluate the effect of influential factors, including longitudinal offset, circumferential offset, incomplete contact of loading shoes, and incomplete contact in the support area. To evaluate the impact of these defects and compare the numerical results, crack width, crack starting force, allowable crack force, plastic strain, and damage parameters were considered. In addition, the impact of mentioned factors is evaluated on the performance of three different segmental lining types, including reinforced concrete segment, recycled steel fiber reinforced concrete segment, and ultra-high performance recycled steel fiber reinforced concrete segment. In this parametric study, the parameters' values were selected based on statistical data of more than 23,000 installed segments. According to the results, it can be said that numerical modeling is able to simulate stress and damage patterns in different conditions accurately. This method can also provide helpful information about the performance of segmental tunnel lining because the repetition of the classical design often uses very simple models, which ignore essential phenomena such as the effect of longitudinal or circumferential offset, incomplete contact of the shoe loading, or in the support area, and excessive thrust force. Numerical analysis of segmental tunnel lining behavior by considering different conditions can reduce undesirable phenomena and, consequently, construction costs.

Mechanical behaviour of shield tunnel linings strengthened by steel plates spanning circumferential joints

Shield tunnel is susceptible to nearby disturbances, resulting in excessive longitudinal differential deformation, which severely affects the structural performance of the tunnel. Reinforcing the tunnel with steel plates spanning circumferential joints was recently proposed to control the longitudinal differential deformation of the tunnel. However, the acting mechanism and strengthening effects of the steel plates need to be further investigated. Firstly, a multi-scale solid ring-spring numerical model was proposed in the ABAQUS software and validated by available field data. Next, the behaviour of shield tunnel linings reinforced with steel plates in the rings (in-ring scheme) and spanning the rings (across-ring scheme) was compared in detail. Results indicate that the stiffness of circumferential joints can be greatly improved by the across-ring scheme, thereby effectively controlling the longitudinal differential settlement and dislocation. Even when the coupling effect of longitudinal and lateral deformation is present, the across-ring scheme can control lateral deformation more effectively than the in-ring one. Overall, the across-ring scheme is more effective in controlling the deformation of shield tunnels, whether it be longitudinal differential deformation, dislocation, or lateral deformation. This research can provide helpful guidance on deformation control of shield tunnels. In addition, it could be broadly applied in engineering.

Numerical characterisation of the rotational behaviour of grey cast iron tunnel joints

The structural assessment of segmental grey cast iron (GCI) tunnel linings to nearby construction is challenging due to the presence of the joints affecting the stiffness of the tunnel lining. This paper presents an extensive investigation, using 3D finite element (FE) analyses, into the bending moment-rotation (M-θ) behaviour of two GCI tunnel joint geometries. These two geometries correspond to standard running and station tunnels of the London Underground network. The contribution of this study is two-fold. i) The novel characterisation of the M-θ response enables the development of new models for simulating the mechanical response of GCI tunnel joints with structural elements which can be used in simplified, 2D geotechnical analysis for tunnel safety assessments. ii) The analyses provide insight into the behaviour of GCI tunnel linings that would be difficult to achieve through experimental and field observations alone. More specifically, the analyses show that when the bolts are removed from the joints the possibility of tensile failure can be disregarded; that the initial bolt preload influences the rotational stiffness only after some rotation has taken place and does not alter the bending moment of opening; and that the out-of-plane displacement restraint has little influence on the joint response.

Thermomechanical behavior of tunnel linings in the geothermal environment: Field tests and analytical study

Geothermal environment brings challenge to the construction and maintenance of tunnels. This motivates the present study on the thermomechanical behavior of the supporting system of these tunnels. Evolution of the temperature and strain fields of the surrounding rock and linings of three representative cross-sections were monitored in field. These sections exhibit significant difference in the initial geothermal temperature, reading as 28.2∘C, 45.4∘C, and 68.6∘C, respectively. The measurements indicate that, with an increase of the initial geothermal temperature, the speed of the temperature drop of the surrounding rock increases after the excavation, whereas the thermal shock resulting from the construction of secondary lining becomes less obvious. Significant tensile strains were observed in the primary lining, as a result of the geothermal environment. This stimulates the establishment of a simplified arch model in quantification of the thermal stresses of the primary lining. The quantitative thermoelastic analysis indicates that the high geothermal environment leads to remarkable tensile stresses at the vault of the outer surface and at the side wall of the inner surface, which counteracts with the released heat from the cast in-situ concrete of the secondary lining. It is concluded that geothermal environment raises the risk of tensile cracking of tunnel linings. Therefore, careful inspection is recommended for its integrity and, thus, for the long-term durability of such tunnel linings.

Dynamic behavior of fault tunnel lining under seismic loading conditions

Dynamic behavior of fault tunnel lining under seismic loading conditions

A novel method of imposing external water pressure to explore the failure behavior of railway tunnel linings

The mechanical behavior of tunnel linings is of paramount importance in tunnel design, especially for tunnels that are subjected to high external water pressure. A novel method is proposed to impose water pressure on a tunnel lining based on the principle of mechanical equivalency. A purpose-built device was manufactured to simulate external water pressure on a horseshoe-shaped tunnel lining. The device thus avoids the abrupt disintegration of the lining material that can occur when actual water is used with test models. The proposed methodology is verified via finite element (FE) numerical modeling by comparing the pertinent bending moments, thrusts, and shear forces. Different hoop tensions were employed to simultaneously apply loads around the upper part of the lining and the invert in order to recreate the effect of the non-uniform external water pressure that acts on real tunnel linings. Tests using our 1:30 scaled models reveal that bending-induced tensile failure occurs at the knees and invert of the tunnel lining. However, earth pressure results in thrust-induced compressive failure of the upper parts of the lining, i.e., the shoulders and roof. Typically, the failure mode under external water pressure is different from that under earth pressure. Consequently, tunnel linings encountering high external water pressure should be based on different design parameters to those subjected to high earth pressure.

Effect of Horizontal Curve on the Response of Road Tunnels under Internal Explosion

Internal explosion in a tunnel is a complex loading phenomenon where the tunnel lining is subjected to not only direct impact of explosion but also loading due to multiple reflection of blast waves which could be of magnitude higher than that of incident blast wave. This kind of loading is complex in nature and difficult to predict using simple analysis tools. Further, it poses a serious threat to its structural integrity. Studies have been conducted in the past to understand the behaviour of tunnel under internal explosion. However, they have been focused on straight tunnels ignoring the convex and concave shapes introduced due to horizontal and vertical curves. Shape of the target surface has significant effect on the characteristics of blast wave. This study investigates the effect of horizontal curves on the damage behaviour of tunnel lining due to internal explosion. A series of numerical simulation are performed on box-shaped tunnel with varying curvature radius and the results are compared with that of straight tunnel adopting Multi-Material Arbitrary Lagrangian-Eulerian (MM-ALE) method using LS-DYNA®. Explosive and air are modeled using ALE formulation, whereas, tunnel and soil are modeled using Lagrangian formulation. Further, Jones-Wilkins-Lee equation of state is used to model the explosion. Damage to the tunnel lining is measured in terms of peak particle velocity (PPV) and von-Mises stress. It is observed that walls of curved tunnels undergo more PPV compared with straight tunnel wherein concave wall show the highest PPV. Propagation of blast wave along the tunnel length is significantly affected due to the introduction of curvature resulting in change in reflection patterns. This further leads to variation in stress contours on tunnel lining with higher concentration of stress in curved tunnels than in straight tunnel.

Study on the Mechanical Response Mechanism and Damage Behavior of a Tunnel Lining Structure under Reverse Fault Dislocation

In this paper, the mechanical response mechanism and damage behavior of a railway tunnel lining structure under reverse fault dislocation were studied. The damage behavior of railway tunnel linings under reverse fault dislocation was validated by undertaking laboratory tests and three-dimensional numerical simulations, where Coulomb’s friction was used in the tangential direction of the interface. The failure damage, which increasingly accumulates with displacements, mainly concentrates in fault fracture neighborhoods 0.5 D to 1.5 D (D is the tunnel diameter) within the footwall. The maximum surrounding rock pressure and the maximum longitudinal strain develop in the tunnel near the hanging wall area. The damage begins as longitudinal cracking of the inverted arch. With the increase in dislocations, those cracks develop upward to the arch foot and the waist. Consequently, those oblique cracks separate lining segments, leading to abutment dislocation. The research results provide technical guidance and theoretical support for on-site construction and follow-up research, and they have important application value.

Cracking behaviour of tunnel lining under bias pressure strengthened using FRP Grid-PCM method

During operational stage, lining cracking is a common anomaly for road tunnels, which seriously affects the integrity and service-life of tunnels. Bias pressure is one of the most important factors that cause lining cracking. In order to provide a novel and effective control method for lining cracking, a series of scale tests regarding the strengthening of tunnel lining using fiber reinforced plastic grid with polymer-cement-mortar (FRP grid - PCM) were carried out, and the effects of various parameters on the control of lining cracking, such as the acting range of bias pressure, the layout range of the FRP grid layer and the number of FRP grid layers were studied. The scale tests were composed of seven specimens, including two reference specimens under different acting ranges of the bias pressure and five strengthened specimens with different strengthening parameters. The inhibitory mechanism of FRP grid layer for lining cracking was also discussed. The results show that the FRP grid layer could effectively bear tensile stress, so that the propagation of the tensile crack was effectively suppressed, and the bearing capacity of the lining was significantly improved. When the acting range of the bias pressure was small, that is, the internal force of the lining section was dominated by the bending moment, the FRP grid layer could improve the rigidity of the lining. More specifically, the gain increased with a concurrent increase in both the number and the layout range of FRP grid layers, whereas it worsened with an increase in the acting range of the bias pressure. The results showed that the FRP grid - PCM method is a potential control method for the tensile crack of the lining.

Experimental study of fire damage to reinforced concrete tunnel slabs

Fire hazards are a major threat to tunnel structures; however, the existing understanding of the behavior of tunnel linings under fire is limited, which restricts cost-effective and safe design of tunnels for fire. The research work in this paper aims to experimentally evaluate and quantify fire damage to tunnel linings considering a combination of influencing factors. The effects of three parameters on fire damage to the ceiling (typically the most damaged area) of a tunnel lining are studied through five furnace tests on large-scale reinforced concrete slabs. The parameters include: (1) concrete composition - presence/absence of polypropylene fibers, (2) the level of structural restraint (induced using post-tensioned strands), and (3) the fire intensity and duration. These parameters are selected to reflect realistic scenarios and provide a rational basis for evaluating tunnel damage, in terms of crack pattern, spalling, discoloration, non-destructive testing, and deflections during fire and after cooling. This research provides vital experimental data for fire damage assessment of reinforced concrete tunnel linings, and assists in verifying numerical models for analyzing structural performance during both the heating and cooling phases of fire.

Study on cracking behavior of tunnel linings with the diseases of void and lining insufficient thickness

Typical tunnel diseases, such as lining cracking, void behind the lining, and lining insufficient thickness, can commonly occur in tunnel structure, seriously threatening the safety state of tunnel operation. In this research, to investigate the relationship between these diseases, the cracking behavior of tunnel structure with typical combined diseases of void behind the lining and lining insufficient thickness were concentrated on using the cohesive zone model (CZM) method. At first, the zero-thickness cohesive elements were inserted between the lining solid elements globally to determine the possible cracking zone, guaranteeing the randomness of cracking. Subsequently, the characteristics of crack propagation of linings with typical combined tunnel diseases were explored detailed under the applied gradual loading. Finally, to quantitatively explore the development of lining cracks, the statistics of cracks (including the number of damaged cohesive elements and crack area) were conducted. The main results of this study indicated that the distribution of void and lining insufficient thickness influences the cracking behavior obviously, and the cracking degree shows a positive relationship with the applied gradual loading. Furthermore, as the gradual loading increases, the number of damaged cohesive elements presents a significant increasing trend, and the number of damaged cohesive elements also shows a positive relationship with the void range. In addition, the crack area also shows a positive relationship with the applied gradual loading and the void range.

Thermal behaviour of unloaded concrete tunnel lining through an innovative large-scale tunnel fire experimental testing setup

A full-scale tunnel fire test requires extensive preparation of the fire source and an empirical design setup of the tunnel to reach 1200 °C of tunnel fire temperature. This paper shows comprehensive experimental research on the method of designing a large scale fire test setup for new unloaded concrete tunnel segments. The thermal and spalling behaviour of fire-resistant Patent- MY-163281 composition concrete (PMC) tunnel lining segments are compared to those of a current construction project coded SPC. The tests were conducted to follow the RABT time–temperature curve. Unloaded tunnel segments were considered to minimise the effects of mechanical loading on the spalling and failure behaviour. The results show that the test setup could replicate the RABT time–temperature curve with a nominal difference. The temperatures decreased gradually, with the increasing depth of concrete cover from the surface exposed to fire, with the PMC segments less than SPC’s. The PMC segments showed good concrete spalling resistance behaviour, but the SPC segments were severely spalled. The PMC tunnel lining showed better performance under tunnel fire compared to SPC lining with similar design strength.

Numerical modeling of twin tunnels under seismic loading using the Finite Difference Method and Finite Element Method

Considerable advances in the development of user-friendly modeling code against the limitations of analytical methods have led to an increase in the utilization of numerical methods to predict the dynamic behavior of tunnel lining under seismic loading. This paper examines the seismic performance of the ZAM (Zaouit Ait Mellal) twin tunnels located between the cities of Marrakesh and Agadir in Morocco, using the Finite Difference Method (FDM) provided by FLAC 2D software, and Finite ElementMethod (FEM) provided by PLAXIS 2D software. The adopted simulated acceleration is obtained from an artificial earthquake event with free-field boundary conditions in the numerical models. Three points are chosen in the tunnel lining: two in the corner and one in the crown. The results show the evolution displacement during the dynamic time for each point, we note different distributions of values in FLAC compared with PLAXIS, which these differences are justified by the type of interface used in both programs.

Simulation of subway tunnel construction process based on fi-nite element analysis

Simulation of subway tunnel construction process based on fi-nite element analysis