Shield Tunnel Segment Research Articles

Experimental and Numerical Study on Damage Characteristics of the Shield Tunnel Segment Under Blast Impact Loading

The impact-resistant capacity of the subway tunnel lining is significant to prevent the subway tunnels from the serious damage under the blast impact loading. In this paper, the light gas gun experiment of the shield tunnel segment is carried out. The impact loading generated by light gas gun is used to simulate the blast impact loading. The strain variation characteristics and the damage crater of the shield tunnel segment are analyzed based on the experimental results. Three-dimensional finite element simulations of the specimens under the impacts of bullets with different velocities are also performed using the dynamic finite element program LS-DYNA, and their reliability are verified by the experimental data. Based on the numerical simulation results, the stress states of the elements of the shield tunnel segment are investigated to understand the damage mechanism. The damage levels of the shield tunnel segment under different blast impact loading are also studied. The relationship model between the impact velocities of the bullets and the impact loading is established. The damage depths of the shield tunnel segments under different blast impact loadings are quantified. Finally, the effect of concrete strength on the damage of shield tunnel segment is studied.

Experimental Study on Mechanical Behavior of Gas Transmission Shield Tunnel Segments

To analyze the mechanical behavior of the shield tunnel segment lining of underwater pipelines, based on the prototype segment structure practically applied in a project, a local model test of the combined shield segment considering front and rear ring staggered joints was designed. The internal forces and strains, joint opening and misalignment, and structural deflection change with the axial pressure ratio at different locations of the segment in the range of axial pressure ratio 0.02–0.54 were investigated, and the final failure form of the segment structure was also obtained. The experiment results show that in the assembly segments, the middle segment has the highest stiffness, followed by the side segments. When the segments are damaged, the maximum opening of the longitudinal joint is 1.75 mm. Because the overall damage of the segments is earlier than the joint damage, it is suggested that the development of structural cracks, joint misalignment, and structural deflection be taken as the basis for evaluating the safety of tunnel segments. When the axial compression ratio is loaded above 0.50, top concrete crush damage occurred in the middle segment, while the concrete on both sides happened to incur an oblique 45° shear damage.

Bending failure performance of a shield tunnel segment based on full-scale test and numerical analysis

Bending failure performance of a shield tunnel segment based on full-scale test and numerical analysis

Evaluation of the antenna parameters for inspection of hidden defects behind a reinforced shield tunnel using GPR

Ground penetrating radar (GPR), as a recognized non-destructive testing method, has been widely applied to detect hidden defects behind a reinforced shield tunnel. However, the scattering of electromagnetic waves caused by the dense double-layer rebar meshes embedded in a tunnel lining severely influences GPR's detection capabilities. Selecting the appropriate antenna parameters is a crucial step before conducting GPR measurements. In this paper, the penetration capability of GPR waves is evaluated using a shield tunnel model made of two shield tunnel segments. The laboratory experimental results demonstrate that an antenna with a center frequency of 400–600 MHz is appropriate for detecting hidden defects behind the concrete segment. Regarding the antenna polarization direction, it is better to set it in the longitudinal direction of the shield tunnel since the rebar spacing is slightly larger than that in the circumferential direction. The antenna height from the concrete segment should be controlled within a fifth of the wavelength in air to compromise between the data quality and detection efficiency. The results will aid in determining antenna parameters when GPR is applied to inspect hidden defects behind a reinforced shield tunnel.

Mechanical performances of shield tunnel segments under asymmetric unloading induced by pit excavation

To explore the stress and deformation responses, as well as the failure characteristics of the shield tunnel segment of Hangzhou Metro under the influences of pit excavation and other surrounding projects, a self-developed “shield tunnel segment hydraulic loading system” was used to carry out full-scale loading tests on the three-ring staggered assembled segments. The structural performances and failure process of the tunnel segment under step-by-step asymmetric unloading were studied. A safety index was proposed to describe the bearing capacity of the segment. Next, a finite element model (FEM) was established to analyze the bearing capacity of segment using the test results. Finally, the effect of reinforcement with a steel plate on the deformation and bearing capacity of the segment was analyzed. The results showed that under asymmetric unloading, the peak value and amplitude of the bending moment on the near unloading side converged with a greater value than those on the far side. The concrete internal force exhibited a directional transformation at different load stages. Cracks first appeared at the 180° inner arc surface of the bottom standard block and then expanded to both sides, while the rate of crack propagation of the outer arc surface was relatively lower. The bearing capacity of the segments can be evaluated by the combination of the factors, e.g. the residual bearing capacity coefficient, moment transfer coefficient, and characterization coefficient. The segments approaching failure can facilitate the increase in the residual bearing capacity coefficient by more than 50%. This can provide guidance for the service assessment of metro tunnel operations.

Seismic Response Analysis of a Shield Tunnel in a Coastal Nuclear Power Plant under a Complex Foundation

As a transportation hub connecting sea and land, the seismic safety of an undersea tunnel is very important. Based on the structural and stress characteristics of a shield tunnel, a seismic response analysis of a coastal nuclear power plant under a complex foundation is carried out in this paper. Firstly, adopting the lateral and longitudinal response displacement methods, the authors study the variation and distribution features of the rate of diameter change and joint-stretching value of the shield tunnel segments. On this basis, a three-dimensional refined finite element model of a sinking tube–soil mass under a complex soil foundation is established. Finally, when the joints and segments of the shield tunnel are subjected to ground motion, the deformation and internal force distribution of its lining segments are studied. The findings show that under influence of SL-2-magnitude ground motion, the soft–hard stratum junction is the weak point of the shield tunnel structure’s longitudinal seismic resistance. When the silt layer at the position of the shield segment is thicker and the geological conditions are relatively poorer, the internal force, diameter deformation rate, and joint-stretching value will be larger. The research results can provide a reference for seismic research on shield tunnels in sea areas under complex foundations.

Numerical Analysis of New Stainless-Steel Corrugated-Plate Reinforcement of Shield-Tunnel Segmental Joints Based on Virtual-Tracking-Element Technology

Shield tunnels inevitably endure various forms of damage as their service times increase. Steel corrugated plates have been used extensively under multiple conditions and have proven effective in strengthening segmental joints, according to full-scale tests. A numerical model is proposed to probe the feasibility of using a new stainless-steel corrugated plate (SSCP) to reinforce shield-tunnel segments. A new method, called virtual-tracking-element technology, is employed to achieve the simulation of a realistic stress state of the segmental joint. Moreover, a segmental-joint-component analysis and a parametric study were conducted based on the numerical model. The results demonstrate that: (1) the virtual-tracking-element technology is a valid and efficient approach to the simulation of the secondary-stress state of segmental joints; (2) SSCP reinforcement is not fully utilized when the grade of segmental concrete is C50, and it has a wide safety margin for potential overload; (3) SSCP reinforcement performs well regardless of the burial depth, and reinforcement in advance is recommended.

Deep learning of electromechanical impedance for concrete structural damage identification using 1-D convolutional neural networks

Common damages in concrete materials and structures are usually in small sizes at initial stage, which induce small stiffness and mass loss being difficult to evaluate severity level merely depending on traditional electromechanical admittance (EMA, inverse of impedance) technique. In fact, several state-of-the-art computerized techniques have been incorporated with the EMA for automated evaluation of concrete damages. However, complicated data preprocessing still limits the efficiency of these techniques in terms of accuracy and computational cost. To this end, this paper proposed a novel deep learning approach using one-dimensional (1-D) convolutional neural networks (CNNs) for exploiting the raw EMA signatures to automatically identify tiny damages in concrete structures, which eliminated tedious data preprocessing for network training and testing. Two independent EMA databases measured by smart piezoelectric sensors were established based on proof-of-concept experiment of slight/severe mass-loss damage detection on a concrete cube, as well as practical application of bolt-looseness identification on a full-scaled shield tunnel segment assembled structure. For both tests, effect of varied dimensions of input data on the efficiency of CNN models were evaluated as well. The well-trained CNN model perfectly quantified the severity degrees of mass-loss and bolt-looseness damages, which demonstrated significant superiority than traditional back propagation neural network and the model with less dimensions of input data exhibited higher accuracy. Delightful results in this work potentially provided a potential paradigm of EMA data-driven tiny damage identification for real-life concrete infrastructures.

Experiments and numerical simulation of the reinforcement effect of channel-steel-reinforced shield tunnel segments under unloading conditions

The increasing emergence of foundation pit excavations in dense urban areas has caused a series of adverse impacts on operating tunnels. Thus, the investigation of tunnel segment reinforcement is crucial and essential for geotechnical engineers. This article intends to investigate the reinforcement effect of the channel steel reinforcement method through a three-ring full-scale test and finite element simulation. The three-ring full-scale test is carried out by considering different confining pressures under the influence of different tunnel burial depths and different distances between the foundation pit and tunnel (clearance distances). In addition, a three-dimensional refined FEM numerical simulation verified by the full-scale model test is conducted to study the influence of foundation pit retaining structure deformation. The research results show that channel steel reinforcement can significantly improve the stiffness of the segment and its bearing capacity. The effect of the channel steel is more prominent in tunnels with a large burial depth. The stress and deformation of the segment are relatively uniform under the conditions of different clearance distances after the reinforcement of the channel steel. The top and bottom convergence of the segment and the bolt stress increase as the deformation parameters of the envelope structure increase; furthermore, the top and bottom convergence of the segment can be reduced up to 46.88% after the channel steel reinforcement.

Experimental Study on the Properties of Mixed-Fiber Concrete Shield Tunnel Segments Subjected to High Temperatures

In order to study the mechanical and damage behavior of concrete shield tunnel segments under a high temperature, two self-compacting concrete and three mixed-fiber (steel and polypropylene fiber) self-compacting concrete test blocks were designed. The influence of several key factors, including fire duration, pre-loading, and concrete type, on the fire behavior of concrete shield tunnel segments were studied. The results show that the type of fiber and pre-loading have an important influence on crack development in concrete shield tunnel segments. Compared with undoped segments, cracks in segments with steel fibers and polypropylene fibers appeared later, and the average crack spacing decreased. The pre-loading has an important effect on the vertical deformation before and after the temperature rise. As the load level increases, so does the deformation after the temperature rise. The influence of the initial load level should be considered when designing the fire resistance of the segment.

Experimental investigation of corrosion effect on bending deflection of shield tunnel segment containing transverse cracks

AbstractCorrosion of the steel rebar will be generated in the cracked concrete of the shield tunnel during the operation period, which will reduce the bending performance of the tunnel segment. In this study, the effect of the rebar corrosion on the bending deflection of the shield tunnel segment that contains transverse cracks is investigated by experimental tests. The initial transverse cracks of the segment are simulated by a bending load device, and the galvanostatic method is used to simulate the corrosion of the segment rebar. The degradation of the segment bending deflection after the rebar corrosion process is measured and compared with the non‐corroded segment. The results reveal that when the depth of the transverse crack does not exceed the thickness of the protective layer, the corrosion of the rebar has little effect on the bending degradation. However, when the width and depth of the transverse crack reach approximately 1.2 and 210 mm, respectively, the degradation rate of bending deflection begins to increase rapidly.

Seismic response of shield tunnel structure embedded in soil deposit with liquefiable interlayer

Shield tunnels are widely in used urban areas and could be constructed in fully or partially liquefiable soil deposits and are thus susceptible to damage during earthquake events. In this paper, a two-dimensional saturated soil-structure dynamic interaction model is developed for shield tunnel lining structures. The model accounts for the nonlinear mechanical behaviors of the shield tunnel segments and joints. It also accounts for the soil nonlinear behavior by employing plasticity models (i.e., PM4Sand and PM4silt for sand and plastic silt/clay, respectively). The seismic response of the shield tunnel structure in soil deposit with liquefiable interlayer as well as the interaction mechanism between the liquefiable soil layer and the tunnel are investigated. The obtained results demonstrate that the sand dilatancy and cyclic mobility behaviors under undrained loading conditions govern the seismic site response and that the presence of tunnel structure changes the site acceleration response and degree of soil liquefaction. It is also found that internal forces and deformations of the tunnel segment joint around the foot and shoulder are significantly larger than that in the rest of joint positions. Therefore, particular attention should be paid to potential damage of joint bolts around the foot and shoulder in a liquefiable soil deposit.

ARTAN SICAKLIK ETKİSİNDEKİ BETONARME TÜNEL SEGMANLARININ SEM İLE SAYISAL OLARAK İNCELENMESİ

There has been increasing concern about the fire-resistant design of reinforced concrete tunnel lines among structural engineers due to the fire incidents that occurred recently. A limited number of experimental works focused on the fire behavior of the conventional reinforced concrete (RC) and hybrid fiber reinforced concrete (HFRC) tunnel segments have been presented in the literature. However, there is no comprehensive numerical study related to RC shield tunnel segments under the effect of elevated temperature. Thus, this study intends to establish a 3D finite element model (FEM) for the evaluation of the fire behavior of RC shield tunnel segments. At the first stage of the presented FEM, the temperature distribution that occurred in the RC tunnel segment was evaluated with a heat transfer analysis carried out. In the second stage, the stress analysis was conducted to calculate the load-displacement behavior of the RC tunnel segment under the combined effect of the gravity load and the elevated temperature. The results obtained from the FEM were compared with an experimental work existing in the literature. The fact that numerical analysis is compatible with experimental results proves that the presented FEM can be used in the determination of the behavior of RC shield tunnel segments subjected to elevated temperature.

Interfacial Behaviour of Shield Tunnel Segment Strengthened by Thin Plate at Inner Surface

The strength and stiffness of a shield tunnel segment can be improved significantly by bonding a steel plate at its inner surface. In this kind of strengthened segment, interface debonding is usually the controlling failure mode, and it strongly depends on the interfacial stresses of the adhesive layer between the segment and the steel plate. To deepen the understanding of the interfacial behaviour, this study proposes a three-dimensional fine finite element (FE) model regarding the interfacial stresses. An existing full-scale experimental result is then employed to confirm the feasibility and accuracy of the proposed model. Further, the fine finite element model is used to calculate the interfacial stress distributions and to evaluate the structural parameters on the interfacial behaviour of the strengthened segment. A high concentration of interfacial stresses exists at the vicinity of the steel plate ends and the joints, which might result in premature failure at these locations. Both the normal and shear stresses at the interface are significantly influenced by the structural parameters. The findings in this study can provide guidance for the optimal design of strengthened shield segment that can prevent premature interfacial debonding.

Quantitative Evaluation Index for Analysis of Assembly Effect on Shield Tunnel Segment Structures

The local force and deformation of shield tunnel will be transferred and redistributed owing to the discontinuous segmental structure. This study develops quantitative evaluation index to explore the influence of the axial compression ratio, eccentricity, and longitudinal force on the assembly effect. A full-scale test is conducted on a single segment and staggered assembled segmental linings. First, the results show that the assembly effect has an obvious redistribution influence on the force and deformation of the segment. Second, the influence of eccentricity on the bending moment is much larger than that of the axial force. The stiffness between rings varied at different positions and the larger the stiffness difference, the more obvious the assembly effect. The results demonstrate that the design and mechanical performance of the shield tunnel under different embedded conditions can be optimized by increasing the longitudinal force, which moderates the assembly effect and ensures the structure reaches the highest bearing capacity.

Modification of Segment Structure Calculation Theory and Development and Application of Integrated Software for a Shield Tunnel

From the aspect of calculation theory, the beam–spring model method and modified routine method of shield tunnel segment structure calculation were improved, and an efficient integrated software system for segment structure calculation of shield tunnel was developed. The beam–spring method is generally calculated according to the assumption of continuous displacement between beams and joints, and the existing modified routine method assumes that the lateral pressure gradient is constant generally, which does not consider the variation in lateral pressure gradient caused by the difference in the lateral pressure coefficient of soil layers or the water level height, which has a certain deviation from the actual situation. The existing beam–spring method and modified routine method theory were improved, the discontinuous displacement between beams and joints in the beam–spring method was taken into account, and the problem of lateral pressure gradient change in the modified routine method was solved. The calculation software system developed by C# and python programming language was proposed to improve the accuracy and efficiency of segment structure calculation. Based on the actual monitoring data of the internal force of the shield tunnel segment and the adjacent shield tunnel segments under construction in Changsha, China, the segments of the shield tunnel with different cross-section sizes and different hydrogeological conditions are calculated to verify the reliability of the calculation software system. At the same time, combined with the calculation results of the software system and field test data, the stiffness reduction coefficient and equivalent foundation resistance coefficient in the modified routine method were derived to further improve the accuracy of the calculation results, which provided a new idea for the calculation of segment structure of shield tunnel with different diameters under different hydrogeological conditions.

Complex Deformation Monitoring of Shield Tunnel Segment Joints Using Distributed Fiber Optic Sensing Technology: Experimental Verification

Complex Deformation Monitoring of Shield Tunnel Segment Joints Using Distributed Fiber Optic Sensing Technology: Experimental Verification

Mechanical behaviour of splicing joints in shield tunnel lining subjected to fire

Shield tunnel segment joints are weak links in tunnel structures; however, studies on their fire-resisting performance are limited. In this study, scaled tests were performed on lining joints to investigate their fire-resisting behaviour in relation to installation errors. The results indicated that the lining segment with initial defects exhibited a large peeling depth, whereas those without initial defects exhibited a large spalling area and shallow depth. Moreover, the damage rate of the lining joints with initial defects was 10.52%, and the lining segment with initial defects exhibited a larger residual deformation after cooling. Furthermore, the bending and shear resistance of the lining joints decreased sharply, which was manifested by an increase in the joint opening angles. The stiffness of the lining joints with initial defects decayed faster, and the stiffness loss was greater than in those without initial defects. After the test, the remaining stiffness was reduced by 69.7% compared to that of the lining joint with no defects. The results obtained can be used to further develop the thermal–mechanical coupling of splicing joint structures in shield tunnel linings.

Relationship between Invert-Filling Disengaging and Deformation of Shield Tunnel Using Staggered Assembled Segment

The disengaging between invert filling and segment affects the safety of train operation. A 3D numerical model of a three-ring staggered assembled shield tunnel is established, which is verified by a full-scale test. On this basis, cohesive element is inserted between the invert filling and tunnel segment to simulate the fracture process of invert filling-segment interface, and explore the relationship between the deformation of staggered assembled shield tunnel and the disengaging of invert filling. The results show that: 1) The development of invert filling disengaging affects the internal forces of shield tunnel segments. 2) The relationship between the development of invert filling disengaging and the deformation of shield tunnel can be four stages. Different segment assembly methods do not affect the variability of the disengaging ratio. Tensile failure occurs in 89% of the interface layer, which is the main form of invert filling disengaging. 3) The relationship between the development of disengaging distance and the deformation of shield tunnel also can be four stages. The faster the horizontal convergent deformation develops in the segment assembly method, the slower the growth rate of the disengaging distance. 4) The faster the horizontal convergent deformation develops in the segment assembly method, the slower the growth rate of the disengaging volume.

Compressive stress-hydrothermal aging behavior and constitutive model of shield tunnel EPDM rubber material

The damage and aging of the ethylene-propylene-diene monomer (EPDM) rubber material significantly impact the attenuation of the shield tunnel's waterproof performance. Furthermore, the compressive stress acting on the rubber material will further exacerbate this consequence. Therefore, it is necessary to explore the time-dependent properties of rubber under compressive stress. In this study, the EPDM rubber was subjected to compressive stress-hydrothermal aging (CS-HA) test at different pre-compression strains, temperatures, and time according to the application environment of the shield tunnel. The rule of compression set (CS) and the variation rule of mechanical properties of rubber materials after aging were investigated, and the reasons for these rules were analyzed. According to the rule of rubber material performance degradation, a constitutive model of EPDM rubber for shield tunnel segment squeezing environment was proposed. Using compression set as the index of material performance deterioration degree, the time and temperature conversion relationship between laboratory aging and service environment aging of the EPDM rubber segment joint was obtained. Furthermore, based on the constitutive model and related parameter expressions proposed in this paper, the attenuation rule of rubber mechanical properties and residual properties was obtained. It was proposed that the service performance of EPDM rubber under compressive stress should be considered when setting the pre-tightening force during the construction of the shield tunnel, and a reasonable pre-compression force should be adopted. This work provides an effective test method and constitutive model for predicting the time-dependent characteristics of the mechanical properties of rubber materials under compressive stress.