Shield Tunnel Segment Research Articles

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.

Improvement study of elastic rubber gasket for shield tunnel segment

ABSTRACT In view of the current design idea of elastic rubber gasket of shield tunnel segment jointsbased on experience, a numerical simulation method is proposed.By adjusting the area and position of the circular hole,the reasonable deformation of gasket holes under compression,the stress concentration at weak parts,the amplitude and distribution of contact stress under the maximum opening amount,the pressure amplitude when the gasket is fully compressed into the groove and the compression deformation curveare analysed comprehensively, and finally three improved sections are obtained.The results show that both the composite section improved by section 1 and the single section improved by section 3 have good waterproof ability.However, considering the adverse factors, such as the quality difference of water swellable rubber due to water absorbent resin and other swellable materials in practical use, the decrease of elastic deformation property of base materials after swelling and the dissolution of swelling agents, the improved section 3 witha single type has a wider applicability.The originality of this paper lies in systematically discussing the improved schemes of elastic rubber gaskets by combining stress state and reasonable deformation.

Study on the Effect of Foundation Pit Excavation on the Deformation of Adjacent Shield Tunnel

With the construction of a large number of urban infrastructures, there will be new engineering loading and unloading behavior around the urban metro built‐up area, and the deformation characteristics of the new tunnel will be more significantly affected by the external environment. In this paper, the damage to shield tunnel structure caused by pit excavation in similar engineering is analyzed. The finite element model, based on the different distances between the foundation pit and the tunnel and the different thicknesses of tunnel segment, is established. The displacement field and the convergent and longitudinal deformation of the shield tunnel segment with different thicknesses are analyzed. The following conclusions are drawn: (1) the excavation of adjacent foundation pit will cause excessive displacement, settlement, and structural convergent deformation of shield tunnel, causing structural damage such as increasing of faulting, water leakage, and seeping. (2) With the decrease of the distance between the tunnel and the foundation pit, the convergent deformation of the tunnel increases continuously, and when the distance is less than 30 m, the increase of segment thickness greatly improves the convergent deformation of the structure. (3) The increase of segment thickness has no obvious effect on the resistance to longitudinal deformation. When the distance between tunnel and foundation pit is less than 50 m, additional protective measures should be taken to reduce the longitudinal deformation of tunnel.

Study on the Adaptability of Shield Tunnel Segments Orthogonal Crossing Grade III Loess Ground Fissure Section

Taking the Xi’an rail transit line orthogonal crossing the ground fissure section as the engineering background, the structural properties and adaptability of the shield tunnel lining segment under the ground fissure environment are carried out. Using the finite element numerical simulation method, combined with the relevant model tests that have been carried out by predecessors, the damage characteristics of shield tunnel lining segment structure under the action of the ground fissure are revealed. The results show that shield tunnel structure is mainly shear deformation, with local bending deformation. Secondly, the principal tensile stress and principal tensile strain at the arch waist and arch foot of segment ring intersecting with ground fissure section are the largest. The relative dislocation between the rings of the shield tunnel near the ground fissure in the hanging wall is the largest, and the opening of arch top ring seam near the ground fissure in the footwall is the largest. Finally, the conventional shield tunnel lining segment structure cannot be directly used in the ground fissure site with a vertical dislocation of 200 mm.

Performance Degradation of Subsea Shield Tunnel Segment Accounting for Concrete Strength Loss and Steel Bar Corrosion

Subsea shield tunnels usually serve in a typical corrosive marine environment. Under the action of chloride penetration and carbonization, tunnel lining segments are often damaged because of concrete strength loss and steel bar corrosion induced concrete cracking during their service life, which seriously degrades the service performance of the tunnels. A systematical experimental and numerical investigation into the performance degradation of subsea shield tunnel segments accounting for concrete strength loss and steel bar corrosion is presented in this paper. The study demonstrates that chloride penetration decreases the peak strength and elastic modulus of the segment concrete by 42% and 46.1%, respectively. The average of the ratio of dissipated energy to the total energy of dry concrete is much smaller than that of water saturated concrete and chlorine solution saturated concrete, and chloride penetration reduces the energy storage capacity of concrete, and the ability to resist damage is weakened. When steel bars corrode for 120 days, the outer cracks continue to extend, and the concrete around the inner steel bars just begin to crack initiation; when corrode for 20 years, the length of the inner cracks gradually exceeds that of the outer cracks, and the inner cracks initiating from different steel bars coalesce with each other and form a continuous failure surface, causing great serious damage to the segment. Due to the difference in concrete strength, for the outer layer, the evolution processes of steel bar corrosion-induced cracks show the characteristics of early initiation, slow propagation, and late coalescence, and those for the inner layer have the characteristics of late initiation, rapid propagation, and early coalescence. During the whole process the propagation speed of the inner and outer cracks appears to be fast first and then slow. Moreover, the study also illustrates that the final state of segment performance degradation after crack coalescence presents the characteristics of whole lamellar exfoliation of the concrete cover.

Recent Advances in the GPR Detection of Grouting Defects behind Shield Tunnel Segments

Injecting grout into the gaps between tunnel shield segments and surrounding rocks can reduce ground subsidence and prevent ground water penetration. However, insufficient grouting and grouting defects may cause serious geological disasters. Ground penetrating radar (GPR) is widely used as a nondestructive testing (NDT) method to evaluate grouting quality and determine the existence of defects. This paper provides an overview of GPR applications for grouting defect detection behind tunnel shield segments. State-of-the-art methodologies, field cases, experimental tests and signal processing methods are discussed. The reported field cases and model test results show that GPR can detect grouting defects behind shield tunnel segments by identifying reflected waves. However, some subsequent problems still exist, including the interference of steel bars and small differences in the dielectric constants among media. Recent studies have focused on enhancing the signal-to-noise ratio and imaging methods. Advanced GPR signal processing methods, including full waveform inversion and machine learning methods, are promising for detecting imaging defects. Additionally, we conduct a preliminary experiment to investigate environmental noise, antenna configuration and coupling condition influences. Some promising topics, including multichannel configuration, rapid evaluation methods, elastic wave method scanning equipment for evaluating grout quality and comprehensive NDT methods, are recommended for future studies.

Study on the selection of inner diameter in shield tunnel segment in soft soil stratum

In the soft soil stratum, problems such as non-uniform settlement, leakage, and loss of bearing capacity occur during a shield tunnel's construction and operation process. The wrong selection of the inner diameter of the shield tunnel segment will even increase the scale of the problem. It has not been clear how the inner diameter of the segment will influence a tunnel's bearing capacity. Thus, a 3D numerical model is built to determine the mechanism between the inner diameter and the bearing capacity. Two kinds of the diameter of shield tunnel, which refer to 5.5m and 5.9m, are analyzed in this model. The results indicate that the deformation mechanism of these two kinds of shield tunnel in both normal loading process and a loading process concerning the surrounding engineering activities; meanwhile, it is found that the shape of the deformed tunnel is like a horizontal ellipse; finally, the deformation mechanism of segment and bolt is further revealed.

Study on cracking behaviors of shield tunnel segment with annular interfacial unevenness under jacking thrust force

As one of the major engineering disasters in tunnel structures, segment lining cracks have significant impacts on the carrying capacity and durability of shield tunnels. This study focused on the lining cracking problems that are induced by annular interfacial unevenness during construction; a three-dimensional finite element model of shield tunnel linings was established that uses particular gasket elements and considers the assembly tolerance between segments and dowel pads at the annular interface. Through the numerical simulation, the lining’s structural deformation and crack propagation in the presence of the annular joint’s unevenness were studied by adjusting the initial gap and the normal stiffness modulus of the dowel pad at the annular interface. The numerical results indicate that the cracks induced by the jacking thrust force are initiated in hang holes in the midspan of the segments and subsequently develop along the longitudinal direction. In addition, the critical thrust loads for crack occurrence and the crack length are directly related to the initial gap and the stiffness modulus of the dowel pads at the annular interface of the segments. Moreover, the higher the assembly tolerance and the dowel pad stiffness modulus, the more serious will be the longitudinal cracks. It is confirmed that the use of appropriate dowel pads can effectively control the initiation and development of longitudinal cracks and enhance the structure’s carrying capacity.

Investigation of the Deformation Characteristics and Bearing Capacity of a Segment Structure of a Shield Tunnel with Cracks

In this paper, the displacement data of a segment lining structure in a similar model test were analyzed in depth based on a field investigation and the analysis of a cracked segment in a metro project. In doing so, we proved the displacement characteristics and bearing capacity of shield tunnel segments with different cracks numbers, lengths, and locations. The results showed that the presence of a crack decreases the overall stiffness of the structure relative to an undamaged segment ring and causes the deformation increases with the same load to increase. One-third of the width of a segment is the demarcation point at which the length of the crack begins to affect the mechanical properties of structure of the lining of the segment. When the length of the crack is larger than one-third the width of the segment, the instability of the structure tends to result in sudden failure. Although an increase in the number of cracks does not reduces the ultimate bearing capacity of the structure further, the deformation of the structure of the lining of the segment increases significantly as the number of cracks increases. compared to a crack at the vault and at the arch waist, the ultimate bearing capacity of the segment is the same when the crack is at the bottom of the arch, but the effects of cracks located at the arch bottom in the structural deformation are the most significant.

Internal force – deformation and corresponding control measures of shield tunnel with a 5.8m diameter under lateral pressure loss conditions

In consideration of the deformation reservation, treatment and repair of the shield tunnel structure in the 100-year service life, the designed inner diameter of the shield tunnel structure tends to increase. However, the increase in the diameter will reduce the overall stiffness of the structure and reduce the shield tunnel’s mechanical properties under load changing conditions. Taking the 5.8m-inner-diameter shield tunnel in Nanjing as an example, this paper establishes a refined three-dimensional numerical model of the shield tunnel and validates the model with the results from a full-scale experimental test. Mechanical responses of the shield tunnel under the influence of the surrounding engineering activities are analyzed, and the structural maintenance and deformation control strategy are also discussed. The research shows that as the lateral pressure coefficient decreases (i.e. when unloading occurs around the tunnel structure), the stress and deformation curves of the structure have a strong nonlinear characteristic: when the lateral earth pressure loss is about 0% to 21%, the structure is in a near-elastic state, and the deformation and internal force response are not sensitive to load-changing conditions; when the lateral earth pressure loss is 21%∼43%, the damage, stress and deformation of the tunnel structure will increase rapidly, indicating that the structure is in the stage of plasticity, which is the critical interval for structural maintenance; when the lateral pressure loss exceeds 43%, the structure reaches total yielding stage. Therefore, the corresponding maintenance and control measures of shield tunnel segment structure are proposed from the aspects of prevention at the source, control in the process and treatment at the end.

Reconstruction of shield tunnel lining using point cloud

This paper proposes a technique for automatically identifying segments and creating parametric as-built building information models (BIMs) of shield tunnel lining using terrestrial laser scanning data. The developed algorithm includes two parts: (i) a robust method for the classification of the point cloud of shield tunnel segments, and (ii) a new cylinder fitting method for the high-density incomplete cylindrical point cloud data. The point cloud classification includes i) the generation of the 2-D unwrapped depth map, ii) the edge detection, iii) the regional growth of the tunnel, and iv) the classification. The cylinder fitting consists of i) fitting with known cylinder direction, ii) obtaining the direction of the cylinder axis, and iii) finding the boundaries of the tunnel segment. The proposed algorithm is utilized to analyze two shield tunnels; the results confirm that the developed algorithm is practical, and the root-mean-square error of the point-to-model distance is only 1 mm.

Numerical Investigation on Crack Propagation and Fatigue Life Estimation of Shield Lining under Train Vibration Load

Dynamic loads such as the train vibration load usually act on the shield tunnel lining in the long term, which could make the initial flaws in shield segment propagate and gradually weaken the robustness of the tunnel structure. In this paper, a three-dimensional numerical model of shield tunnel lining structure with the initial defect is built to study its dynamic reaction and fatigue crack propagation under the train vibration load. Furthermore, the damage to intact shield segment caused by train vibration load is studied by employing the rain-flow counting method and the Miner damage theory, and a rational fatigue life estimation for the concrete shield tunnel lining is finally made. Results show that crack propagation is influenced by both the train speed and train axle, the higher the train speed, the longer the final crack, and train axle has a larger influence than train speed on the crack propagation in shield tunnel segment. The shield tunnel lining structure of Nanjing Metro Line 5 can meet the demand of working for a hundred years under the current working conditions.

Analytical Study on the Transverse Internal Forces of Shield Tunnel Segments due to Adjacent Excavations in Soft Clays

Deep excavations unavoidably cause the changes in stress and displacement of surrounding soils, which further generate additional internal forces on the adjacent existing tunnel segments, and compromise the performance and stability of the tunnels. In this study, two-stage analysis method is used to theoretically calculate the additional internal forces in the tunnel segments due to laterally adjacent excavation. Based on an empirical deformation curve of diaphragm walls, the excavation-induced stress in a linear elastic soil is formulated using source-sink imaging method. A distribution model of additional external load acting on the tunnel segments due to adjacent excavation is further established, and the additional internal forces in the tunnel segments under the corresponding additional loads are estimated using elastic equation method. Parametric studies are then conducted to investigate the effects of excavation procedure, buried depth of shield tunnel, and excavation-tunnel horizontal distance on the additional internal forces in the tunnel segments. The results show that the studied parameters have significant effect on the additional internal forces in the tunnel segments due to laterally adjacent excavation. When the excavation-tunnel horizontal distance is less than the excavation depth, the accompanied effect on the additional internal forces in the tunnel segments is highly sensitive. This study can provide theoretical insights into the estimation of tunnel segment responses due to laterally adjacent excavation.

Experimental and Numerical Research on Defective Shield Segment under Cyclic Loading

The retaining structure of a shield tunnel is usually subjected to static loading; however, cyclic loading such as the vibration loading of the train will act on the lining structure year after year that cannot be neglected. Due to the complex manufacturing and assembling process of the lining segment, initial defects in the segment are inevitable. Such defects will propagate under the cyclic loading such as the train vibration, which may cause a large threat to the shield tunnel system. In this paper, a defective shield tunnel lining segment under cyclic loading is studied by both a full-scale experiment and three-dimensional numerical simulations to investigate its fracture properties and failure mechanism and make a rational estimate of its fatigue life. Results show that crack propagation of the defective shield tunnel segment can be identified as several different stages based on its deformation characteristics, and the failure pattern of the segment is determined by its initial defects. The results by the experiment and numerical investigation are in good agreement for each other.

Theoretical Solution for Failure Mechanism ofCircumferential Joint of ShieldTunnel Segment Connected Using Diagonal Bolts

Theoretical Solution for Failure Mechanism ofCircumferential Joint of ShieldTunnel Segment Connected Using Diagonal Bolts

The effect of the force between rings of large-diameter shield tunnels on the segmental cracking in weak stratum

Large-diameter shield tunneling in weak strata has the risks of segment floating, segment cracking and seepage, affecting the durability of the tunnel structure. In this paper, the statistical analysis of the cracks of a large-diameter shield tunnel segment was carried out, and the thickness of the force transmission liner was studied. The experiment showed that the average number of cracks per ring was the smallest when using a 3mm liner. Based on the structural characteristics of the segment, four types of stresses, namely simple support of segment boss, double-sided cantilever, single-point cantilever and two-point cantilever, and it is verified through on-site statistics, which has certain guiding significance for crack prevention.

Deep learning based method of longitudinal dislocation detection for metro shield tunnel segment

This paper presents a longitudinal dislocation detection method using an accurate tunnel segment joint labeling algorithm featured by deep CNNs (Convolutional Neural Networks). This method is proposed to be four steps. First, a mobile scanning system is used to acquire 3D point clouds of metro shield tunnels. Then, we use cylinder projection to generate tunnel surface depth images from 3D point clouds for segment joint labeling. Subsequently, two deep CNNs are designed to accurately label the segment joints on the depth images. The first CNN can roughly locate the segment joint positions, and the second precisely label the segment joints. Based on the labeled segment joints, two point data sets are obtained on both sides of each segment joint. By using the RANSAC algorithm, the two point sets can fit into two planes, the equation of which is then calculated to generate the dislocation value of the tunnel segment. Experiment results show that this method can label segment joints integrally and accurately without being affected by nearby tunnel equipment. Compared with traditional image edge detection algorithms (Canny and Sobel with Hough Transform), the CNNs are more powerful in labeling segment joints. When the distance measuring accuracy of scanner is 1.2 mm + 10 ppm, the internal and external accuracy of our detection method are evaluated to be 0.4 mm and 0.9 mm respectively. Compared with the scanning line method, the external accuracy of our method is higher and more reliable when there is tunnel equipment around segment joints.

Investigation on the Influence Caused by Shield Tunneling: WSN Monitoring and Numerical Simulation

Traditional monitoring techniques are faced with the problems of low acquisition frequency and easy to be affected by the construction environment during the shield tunneling, which cannot meet the actual needs of timeliness monitoring of surrounding environmental impact on shield tunnel construction. Based on this actual demand, a wireless sensor network (WSN) system was used to monitor the response of shield tunnel segments and surrounding buildings during the shield tunneling in this study. According to the result of the signal transmission test, an optimization scheme of microelectromechanical system (MEMS) sensor layout is designed to improve the monitoring efficiency of the WSN system. Through the comparative analysis of WSN system monitoring data and traditional monitoring data, it is found that, with the increasing distance between the monitoring section and the tunnel face, the convergence value of tunnel lining clearance gradually tends to be stable, and the wireless monitoring results of transverse clearance convergence of the tunnel in this section are consistent with the overall deformation trend of the convergence gauge monitoring results. This study also simulated the shield tunneling adjacent buildings using a nonlinear finite element method. A parameter sensitivity analysis of the support pressure of the excavation face and the grouting pressure at the tail of the shield is carried out. The results show that the surface settlement can be reduced by properly increasing the grouting pressure and the support pressure of the excavation face. Moreover, increasing the support pressure of the excavation face has a better inhibition effect on the settlement of the surface soil than increasing the grouting pressure.

Control of Strata Deformation in Subway Interval Tunnels Crossing a High-Speed Rail Shield Tunnel at a Short Distance

The construction of subway interval tunnels at a short distance from existing buildings and engineering structures in cities is often a high-risk project. This research discusses subway interval tunnels crossing a high-speed rail shield tunnel at a short distance based on numerical simulations and on-site monitoring. The deformation patterns of the interior of tunnel, ground, and shield segments are analyzed, and the principle and function of reinforcement measures for deformation control are presented. The results indicate that constructing a temporary inverted arch using bolting and shotcreting as per the bench method has higher integral stiffness, and thus, the foot-locking effect of anchor pipes to reduce strata deformation is fully utilized. The deformation of upper high-speed railway shield tunnel segments induced by the construction of subway interval tunnels primarily occurs within a distance three times the diameter of the tunnel. Thus, this is the key area to install advanced support to control tunnel deformation. A compound advanced support approach including pipe sheds and deep-hole grouting is proposed that can exert the arching effect of deep-hole grouting and beam effect of pipe sheds to control strata deformation.

Analysis of Structural Response of Subway Shield Tunnel Lining under the Influence of Cavities

The existence of cavities behind the shield tunnel lining can cause cracking, broken pieces, water leakage, and other problems, which reduces the durability and safety of the shield tunnel segment structure. In order to clarify the mechanism of cavity damage, a more systematic study of the effects of cavities on the shield tunnel lining structure from the angle, depth, and the number of cavities is carried out using model tests and numerical simulations without considering the effects of the stiffness reduction effect at the tunnel segment joints and groundwater seepage in this paper. The findings show that the bending moment value and the cavity angle value are approximately linear with the increase of single cavity angle, and the bending moment at the vault arch is reversed when the angle of the cavity behind the arch is greater than 30°. With the increase of single cavity depth, the axial force and bending moment at the cavity increase, and the distribution of bending moment remains unchanged, and the bending moment tends to be stable and unchanged beyond a certain depth. With the increase of single cavity angle and depth, the structural safety coefficient of the segment decreases, and the degree of influence is angle value > depth value. The existence of multiple cavities intensifies the influence of each cavity on the segment, especially when there are cavities behind the top and bottom of the vault; the bending moment value of the top of the vault increases by 22.53% compared with that of the single cavity condition.