Tunnel Joint Research Articles

Design of a distributed optical fiber sensor system for measuring immersed tunnel joint deformations

Monitoring the deformations of immersed tunnels is important during the entire tunnel service life to assess the structural integrity of the tunnel. Conventional joint deformation monitoring is based on manual levelling measurements and normally occurs only at multi-year intervals, which does not allow to capture short term deformation behavior. In this study a new joint monitoring system using distributed optical fiber sensors (DOFS) is developed. A special sensor layout is designed that allows simultaneous measurements of both horizontal joint opening and vertical uneven settlement of the immersion and dilation joints. For this sensor scheme the transfer relation from fiber strain to joint deformation is derived and verified by in-lab experiments. The sensor system proves to be able to detect sub-millimeter joint deformations, indicating a more than sufficient accuracy for structural monitoring of immersed tunnel joints. Subsequently, the First Heinenoordtunnel in the Netherlands is instrumented using this distributed optical fiber sensing system, in order to obtain additional data for both long-term and short-term assessment of its structural condition.

Behavior of deformation joints of RC utility tunnels considering multi-hazard conditions

Utility tunnels have been widely constructed worldwide to accommodate the lifeline infrastructure and ever-expanding municipal needs caused by fast population concentration and urbanization in recent years. Typical reinforced concrete utility tunnels consist of tunnel segments no longer than 30 m in length and deformation joints between adjacent segments. Although extensive research has been carried out on the seismic behavior of utility tunnels using shaking table testing and numerical method, little progress has been made in the understanding of the mechanical behavior of deformation joints under differential settlement and earthquake ground motion. Engineering practice has demonstrated that the deformation joints also play an important role in ensuring the functionability and durability of utility tunnels. In this research program, two groups of eight test models of utility tunnel deformation joints with shear dowel bars were constructed and tested under monotonic and reversed cyclic loading respectively, aiming to simulate the responses of the deformation joints subjected to differential settlement and earthquake excitation. Both ends of each shear dowel bar were inserted into adjacent segments for certain length, where one end is bonded with the segment concrete while the other debonded to allow for potential longitudinal movement due to temperature change. Concrete strength, dowel bar amount, insert length and layout were considered as the test variables. Test results indicated that concrete strength has little influence on the shear capacity of deformation joints. Placing dowel bars only at two vertical sides of the tunnel box-section can improve the deformation capacity and avoid concrete cracking at the bottom slab of the deformation joints. The reversed cyclic loading test results showed great seismic performance of the test models with great load bearing capacity, ductility, energy dissipation and stiffness. Although arranging all dowel bars at side walls can reduce the cracking of bottom slabs, the ductility and energy dissipation capacity are less favorable compared with placing dowel bars all around the box-section. In addition, although 10d is sufficient for the dowel bar insert length, it is suggested that use of 15d can help prevent severe concrete damages. The numerical analysis verified the test results and can be used for further study of the deformation joints of utility tunnels.

Heat transfer enhancement method for high-voltage cable joints in tunnels

A cable joint is regarded as a hot spot in the cable line. Especially for the case of high loads, a cable joint is prone to overheating, which can eventually cause electrical accidents such as explosions. There is still a lack of heat transfer enhancement methods to address this overheating. In this study, a forced convection method of applying cooling fan for cable joints in tunnels was proposed. Combined with the heat transfer characteristics and structural characteristics of cable joints, a forced convection thermal rating (FCTR) model was established. The effects of cooling fan positions and air velocity on cable joint heat transfer enhancement performance were determined using the FCTR model. The results show that the optimal position for a cooling fan is segment C1/C2 of a cable joint. At this position, the recommended air velocity is 4 m/s. This is because the heat transfer enhancement performance of cable joints at a higher air velocity is almost the same as that when the air velocity is 4 m/s. Based on the experimental measurements, the maximum error of the FCTR model is 2.2%. Compared with the previously reported model, the FCTR model is conducive to obtaining a more accurate conductor temperature with the accuracy improved by 4.8%. The results of this study can provide more accurate theoretical guidance for evaluating the heat transfer performance of cable joints in engineering.

Deformation Characteristics and Damage Assessment of Prefabricated Frame Tunnels after Central and External Explosions

The urban social environment is complex and changeable, and there are accidental and non-accidental explosion risks in tunnels. Performance analysis and assessment after tunnel explosions has become important work. In this study, a prefabricated frame structure (single-layer and double-layer) for urban road tunnels was designed. A three-dimensional refined dynamic response numerical model of a frame tunnel considering the joint effect was established, and the reliability of the modeling method was verified by a full-scale explosion test. Considering factors such as the explosion equivalent (100, 200, 300, and 400 kg), explosion distance (3, 6, 9, and 12 m), and central and external explosions, the deformation characteristics and damage evolution law of the prefabricated frame tunnel after the explosions were explored. The deformation failure mode of the prefabricated frame tunnel was analyzed. The study shows that the roof of a single-layer tunnel and the mid-partition of a double-layer tunnel are weak components of a prefabricated frame tunnel with steel column joints under a central explosion load. The deformation and damage at tunnel joints are greater than those at other positions. Under an external explosion load, the closer the explosion point is, the greater the damage and deformation of the prefabricated frame tunnel lining are. Furthermore, showing a high degree of locality. With the equal amplitude increase of the detonation distance (3–6 m, 6–9 m, 9–12 m), the lining displacement is relatively reduced by about 75.7%, 39.9%, and 10.0%, respectively, and the lining deformation is mainly represented by the overall bending deformation.

Transfer matrix method for analyzing dynamic response of multi-span elastically supported SFT under moving load

This paper proposed a new theoretical model for analyzing the submerged floating tunnel(SFT) under moving load, whose boundary at two ends was regarded as elastic constraint, and the anchor cable was simplified as the discrete spring support. Besides, the tunnel joint was simulated as a flexural spring to connect two adjacent tube segments. The modes and natural frequencies of the model were solved by transfer matrix method, and the dynamic response of the SFT under moving load was investigated by the modal superposition method, which was verified by comparing with the results obtained by the general FEM software. The influence of boundary conditions, dissimilarity of cable stiffness and joint flexural stiffness on the dynamic response of the SFT was analyzed. The difference of the response between the beam on elastic supports (BOES) and the beam on elastic foundation (BOEF) was compared. The results showed that the boundary conditions had little influence on the vibration response of SFT's intermediate spans, but had great influence on the displacement and bending moment of the side span. Besides, even in the case when the frequency differentials of the BOES and the BOEF were small (1.84%), the displacements of the two models also had significant difference. The disparity of the cable stiffness and joint flexural stiffness had great influence on the distribution of displacement and bending moment of SFT.

Failure Mechanism Analysis and Optimization Analysis of Tunnel Joint Waterstop Considering Bonding and Extrusion

In waterproofing mountain tunnels, the tunnel joint is the weak link. To explore the waterproof failure mechanism of the tunnel joint waterstop belt and to propose an optimization method for the waterstop belt, this paper combines tests and numerical simulations, summarizes the waterproofing mechanism of the waterstop belt, establishes a finite element model of the waterstop belt considering bonding and extrusion, and studies the waterproofing ability and mechanical properties of the waterstop. The main conclusions are as follows: (1) The waterproofing capacity of the water stop belt depends on its surface contact pressure and bonding force. (2) Waterstop deformation will partially destroy the bonding between the waterstop and concrete, reducing the reliability of the waterproofing mechanism. (3) When the deformation of the waterstop belt reaches a certain degree, its stress value is too large to meet the requirements of its service life. (4) The design can be optimized from two aspects: the bond between the waterstop and concrete, and the size of the waterstop.

Experimental study on effect of ductile-iron panel stiffness on mechanical properties of segmental joints of shield tunnels

In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels, as the axial force at the segmental lining decreases, the bolt load at the segmental joint increases. It is essential to adopt high-stiffness segmental joints to improve the bearing capacity and control the deformation at the joint position. When designing high-stiffness segmental joints, the selection of ductile-iron joint panel is crucial. In this study, two types of segmental joints with different joint panels were fabricated, and the effects of joint panel stiffness on the mechanical properties of segmental joints were analyzed through full-scale sagging and hogging bending tests. The results showed that the failure mode of high-stiffness segmental joint was similar to that of large eccentric compression section. According to the difference of panel stiffness, the failure modes can be specified into two types. If the stiffness is sufficient, the joint failure occurs due to the yielding of bolts; otherwise, it occurs due to the large deformation of ductile-iron joint panels. As for the design requirement of segmental joint, the stiffness of joint panel should be sufficient, i.e., the opening and failure of the joints are finally induced by the bolt deformation. Otherwise, before the plastic deformation of the bolts, the large deformation of the joint panels will occur under a bending-moment-dominant load, and the bearing capacity of the joints will greatly decrease.

Long-Term Evolution of Joint Leakage and Joint Opening for Shield Tunnel in Soft Soils Deep under Seabed

Long-term leakage at the tunnel joint induces significant tunnel deformations, which in turn aggravates the joint leakage. A finite element model (FEM) model with a defined leakage element incorporated in a segmental joint is developed to investigate the evolution of joint leakage and deformation. Subsequently, a series of parametric analyses are conducted to reveal the time-dependent law of joint opening and leakage variation with leakage location, water head, and waterproof capacity based on Qiongzhou Strait tunnel. The results show that the interaction between joint opening and leakage undergoes a dynamic evolution process during the long-term operation of the tunnel. It is found that the joint opening on the extrados is much more critical and hazardous than that on the intrados, and the synthetic action of water head and waterproof capacity can remarkably delay the development of joint opening and leakage. For Qiongzhou Strait tunnel, the joint opening on the extrados occurs after at least 30 years of initial leakage at the springline and increases to 1.28 mm, and the leakage rate increases from 0.909 × 10−4 m3/d to 1.508 × 10−4 m3/d after 120 years. It is suggested that the waterproof capacity and initial leakages near the springline should be strictly controlled to ensure the long-term safety of the tunnel.

Parameter Sensitivity Analysis of a New Fabricated Rectangular Tunnel Joint Using Numerical Method

An assembled rectangular tunnel has the advantages of high space utilization rate and strong urban applicability. This solution has been widely used in urban underground traffic construction. During their construction and operation, the joints are the weakest parts of the structure. The mechanical behavior of joints is closely related to the safety of the tunnel; thus, it is important to use a joint with good mechanical behavior. This study presents a new type of joints for shallow buried assembled rectangular tunnels. To evaluate the effect of design parameters (tenon depth and tenon angle) on the behavior of joints, the finite element method was used. At the same time, the mechanical behavior of rectangular tunnel joint was analyzed and compared with that of a traditional straight joint under the same loading conditions, showing better results. The performance-based engineering (PBE) concept was implemented to evaluate the robustness of rectangular tunnel joints. The results show that if the bolt is placed on the tensile side of the structure, it provides a strong restraining effect on the deformation of the joint. When the tenon depth and angle are 0.8 m and 3.6°, respectively, the overall behavior of the rectangular tunnel joint was improved. The new type of assembled rectangular tunnel joint designed in this study has a good application prospect in a shallow stratum and provides new ideas for the design and construction of such tunnels.

Full-scale testing and numerical modelling of segmental-joint performance with corroded bolt

Water leakage through segmental joints often occurs for shield tunnels built under groundwater. Chloride ions in groundwater can cause the corrosion of steel bolts in segmental joints, reducing the rigidity of the tunnel lining and endanger the operation safety of tunnels. In this paper, the impact of the corrosion of the steel bolt on the structural performance of segmental joint was investigated using six full-scale segmental joint tests and a series of numerical simulation. Both the experimental and numerical results indicate that the segmental-joint performance can be divided into three stages under different loading and corrosion states. The bolt corrosion can reduce the waterproof ability, bending stiffness, and ultimate bearing capacity of the segmental joint. The impact of the bolt corrosion is most significant in the second stage. Furthermore, the bolt corrosion has a larger impact on segmental-joint performance under a positive bending moment than under a negative bending moment, owing to the configuration of the joint. The impact of the bolt corrosion is strongly dependent on the loading state of the tunnel joint and the corrosion ratio of the bolt.

Construction of twin tunnel in weak and blocky rock mass by using arch supporting method

Design of tunnel excavation and support system in weathered and blocky rock mass is usually a principal challenge in tunneling. In this study, the excavation method of twin tunnel was newly taken into consideration in the condition of weak rock mass, the section size of tunnel was reasonably determined, and new supporting method was established. Firstly, the mechanical characteristics of the project rock mass were determined in each section of tunnel using in-situ point load test (PLT) and RocLab software. Then, design of twin tunnel excavation from mono-tunnel excavation in the weak parts of rock mass was proposed and section of twin tunnel joint was reasonably determined based on the safety and stability of the twin tunnel joint by FLAC3D. Finally, the sequential excavation method of combining top heading and benching with arch supporting method (ASM) was newly proposed and the validity of this method was determined by the numerical simulation modeling. Introducing ASM for the support system ensured the support strength in the excavation tunnel. Advanced excavation scheme and the support system have been successfully applied to ensure the safety and conveniency of the target tunnel construction, with about twice reduction of construction time and 1.5 times raising of stability factor. As a result, proposed method in this paper can be used to all manual tunnelling and underground structures in weak and blocky rock mass.

Study of the mechanical behaviour and damage characteristics of three new types of joints for fabricated rectangular tunnels using a numerical approach

Joints are the weakest parts of prefabricated tunnels, and it is important to consider the material nonlinearities, mechanical properties and complex behaviours of joints in structural design. Based on existing joints, this paper proposes the design of three new types of joints for fabricated rectangular tunnels, including self-weight mortise and tenon joints, bolt mortise and tenon joints and steel plate mortise and tenon joints. To explore the mechanical behaviour and damage characteristics of these new joints, three-dimensional finite element numerical models are established with a plastic damage model to reflect the nonlinear mechanical characteristics of each component of the joint. The results of the numerical analysis are compared with experimental data, verifying the validity of the process. Then, the compressive and bending capacity, steel reinforcement bar stress and concrete damage characteristics of rectangular tunnel joints under different combinations of axial loads and displacement loads are defined. It is indicated that the mortise and tenon joint type significantly affects the damage evolution process of the concrete at these joints. Among the three joint types, the bolt mortise and tenon joint has the largest damage area of concrete and, consequently, the most damage elements due to its reasonable joint structure. Hence, from the perspective of the mechanical performance of the structure, the bolt mortise and tenon joint provides the largest flexural bearing capacity and structural safety, followed by the steel plate mortise and tenon joint. The self-weight mortise and tenon joint has the smallest flexural bearing capacity, but it is the simplest joint proposed and is easier to construct than the other two joints.

Semi-analytical thermo-mechanical model for the shield tunnel segmental joint subjected to elevated temperatures

The segmental joint is the most critical component for determining the mechanical response of concrete segmental linings in a shield-tunnel structure. Existing segmental joint models have been developed mainly for the analysis of segmental lining design, but in the event of a fire, the conditions that a tunnel joint may experience could well exceed the normal design range. Consequently, the validity of the existing segmental joint models becomes questionable. In this paper, an improved semi-analytical thermo-mechanical model is derived based on the general plane joint model to consider the thermal effect induced by elevated temperatures. As a benchmark for the development of the model, a laboratory experiment was conducted on concrete lining segmental joints under elevated temperatures. The general heat transfer and special heat flow invading through the joint were deduced by theorical and numerical methods. A finite element (FE) model is developed and calibrated against experimental model tests, whilst the FE model is employed to generate the required parametric data, from which a fitting function is created. A temperature adjustment coefficient is introduced to improve the calculation of the joint section temperature field. The influence of elevated temperature and axial force on the bending moment of a segmental joint is also incorporated according to the stress state of the joint section. The validation of the proposed semi-analytical thermo-mechanical model is demonstrated through comparisons with the results of fire tests. Finally, the influences of the heating curves, bolt location, and axial load on the rotation stiffness of the joint are investigated using the proposed model.

Preliminary Design for Segmental Joint of Precast Tunnel Liner

Abstract Responses of the segmental tunnel liner to external forces are primarily dependent on complicated interactions among construction process, soil structural interactions, segmental (longitudinal) joint characteristic etc. However, most proposed liner’s design procedures and recommendations are basically empirical and experience based, especially when the roles of tunnel joint are concerned. In the present study, a preliminary design calculation for the segmental joint with consideration of three practical conditions was proposed. The method adopts two main assumptions; the stiffness reduction factor and simplified pre-stressed concrete blocks, so that the flexural capacity of the segmental joint and its interactions to the main reinforced concrete segment body can be designated. Calculation examples are given for three most probable cases, namely, 1) the unbolted joint without joint opening, 2) the bolted joint without joint opening and 3) the unbolted segmental joint with allowing joint opening. Based on these calculations, the required compressive strength of concrete, thickness of liner, steel reinforcement, bolts and number of segments of the liner could be specified. The proposed method could well provide an engineer a tool to determine the initial joint configuration and its interaction to the overall tunnel lining.

Research on Waterproof Performance of Prefabricated Utility Tunnel with Different Types of Joints

In the waterproof system of prefabricated utility tunnel, rubber gasket is usually used at the joint of adjacent pipes. The waterproofing effect of prefabricated utility tunnel joint is mostly judged by the field water injection test and the practical effect of former project. In this paper, the finite element software ANSYS is used to carry out the finite element simulation for three types of joint waterproofing of prefabricated utility tunnel. Considering the uneven settlement of utility tunnel foundation, the influence of different staggered joint installation spacing on the waterproofing of the joints is analyzed. Thus, suggestions are provided for the selection of utility tunnel joint. For the prefabricated utility tunnel with side+end face and double-side joint waterproof type, the longitudinal distance between socket joints should be constrained within 3mm after the joint is installed. It is suggested that the end face+side joint waterproof type should be used for the collapsible foundation, and the longitudinal displacement of the control socket and socket should be less than 3mm. For non-collapsible and settled foundation, double-end joint waterproof type or side+end joint waterproof type can be selected.

Large scale shaking table model test and analysis on seismic response of utility tunnel in non-homogeneous soil

Underground utility tunnels are the most fundamental and reliable lifeline network in urban cities, and are widely constructed throughout the world. In urban areas, most utility tunnels usually encounter the non-homogeneity of subsoil condition due to various construction effects. Studies have shown that the damage mechanism of shallow underground structures mainly depends on the inhomogeneity of the subsoil conditions. This would become a considerable factor for the stability of the underground utility tunnel structures. However, this type of research still needs to establish the vulnerable seismic design. In this study, a series of shaking table tests were conducted on non-homogenous soils to investigate the performance of seismic interaction between utility tunnels, surrounding soils and interior pipelines. The dynamic responses measured from the test account for the boundary condition of non-homogeneous soils, the internal forces, displacement of tunnel joints, the dynamic characteristics on interior pipelines and the reasonable spring stiffness with damping in the seismically isolated gas pipeline model inside the tunnel. The vulnerability of underground utility tunnel in non-homogeneous soil zone and the mechanism of the stability of interior facilities are the main topics discussed in this paper.

Experimental study on mechanical behavior of the skew joints of shield tunnels under large eccentric compressive loading

The existence of joints in shield tunnel lining rings contributes to various deformation problems, such as leakage, joint opening, cracking and dislocation, which will severely impair the safety and durability of tunnel structures. Laborious experiments having tried to work out the mechanical properties of joints, none have drawn attention to two special segmental joints existing in Shanghai metro shield tunnels, which are obliquely intersecting the frontal plane of the lining ring and thus appear askew compared with the rest. The study investigated segmental specimens with the K-shaped top block and its two adjacent segments, including two skew joints connected using straight bolts. Given two groups of experiments, their mechanical behaviors throughout the failure process when subject to a positive and a negative bending moment showed that the bending moment’s impact on bolt strain, joint opening and segmental rotation could be illustrated by two stages when the bending moment was positive and four when negative. Besides, the joint compression height slightly decreased under both conditions and tended to be stable after bolts yielded when subject to a negative moment. The joint opening angle was proved equal to the sum of the segmental rotation angles from both sides of the joint, indicating the individual segment could be regarded as a rigid body. Moreover, the maximum joint opening width increased linearly with the joint opening angle, so did the deflection at the joint position with the segmental rotation. Above all, the skew joints examined behaved similarly to but differently from those of straight joints as there happened strain advance of the bolt and the concrete at one side and strain lag at the other side, which would probably become more obvious as steeper the oblique angle of the skew joints grew.

Optimization Study on Longitudinal Joints in Quasi-Rectangular Shield Tunnels

There are large bending moments in quasi-rectangular shield tunnels due to their deviation from the circular shape, and as for other types of shield tunnels, the longitudinal joints are the most critical parts in the lining structure. A new type of joint with ductile iron joint panels (DIJPs) was installed in quasi-rectangular tunnels to solve these problems. The distance from the bolts to the segment’s inner surface was improved for better performance under specific bending moment types. Both tests and finite element modeling (FEM) simulations were conducted to investigate the effect of the bolt position improvements. The resistances to crack appearance increased by 33.6% and 18.0% for positive and negative moment cases, respectively. The resistances to crack penetration increased by 13.8% and 18.4% for positive and negative cases. From the FEM approach, it was found that the behavior of the joint under the design bending moment range can be divided into three stages, whereby the bolts are only active from the second stage on. The effects of other optimizing methods, such as enhancement of concrete properties and increase of bolt diameters and numbers, are explored. Through comparison, it is believed that optimizing the joint section to increase the lever arm between bolts and the compression zone can improve the joint behavior most effectively. This optimization direction is recommended when designing a shield tunnel joint with DIJPs.

Waterproofing behavior of sealing gaskets for circumferential joints in shield tunnels: A full-scale experimental investigation

This work was performed to investigate the waterproofing and mechanical behavior of sealing gaskets for circumferential joints in Tianjin metro line Z2 tunnel by a full-scale experiment. A newly developed device was introduced in detail, with test procedures, essential treatment methods, and the adopted specimens for gaskets and reinforced concrete segments. Four types of EPDM and composite cross-section gasket profiles were tested under different combinations of joint openings and offsets. The gasket mechanical performance was examined through the load versus deformation relationship, while the water pressure versus joint opening relationship was applied for identifying the gasket sealant performance. The effect of gasket opening area was then discussed, based on a comparison of the test results from two similar gasket profiles. The ratio of waterproof capacity to average contact pressure was proposed to analyze the correlation between the gasket mechanical and sealant behavior. The results showed that both of the joint opening and offset had a great influence on the gasket waterproof behavior, which generally exhibited a reduction with larger joint opening and offset. A relatively small change in gasket opening area may lead to a greater degree of variation in the gasket mechanical and waterproof performance. The leakage failure analysis indicated that bolt holes, circumferential joints and concrete cracks were the common leakage points during the tunneling construction and operation. The full-scale experimental methodology in this paper had the potential in detecting detailed leakage process of gaskets.

Simulation and Analysis on the Mechanical Properties of a New Slide-in Joint for Shield Tunnel Segment

There are many joint forms of shield tunnel lining segments. The new types of joints mainly include plug-in type and slide-in type where few researches concerning whose mechanical properties. This paper aims to construct a full-size numerical simulation model of the selected slide-in quick coupling joint and accomplish a fine prefabricated model. Given the complexity of the mechanics on the joint, loading and constraints are designed into the simulation model which achieves a successful simulation on various working conditions. The numerical results show that joint deformation can be reduced by optimizing the connectors’ position; A strengthening on the structure of C-type embedded groove can improve the overall bearing capacity of segment joint; Axial force can significantly reduce the deformation of the joint. Therefore, this research will help facilitate the effective design of the new type of shield tunnel joint.