Large-diameter Shield Tunnel Research Articles

Performance-based analysis on fire behavior of shield tunnel joint with DDCI connector

In recent years, there has been significant advancement in large-diameter shield tunnel technology, with the continuous emergence of new joint types. To meet the different requirement of application, numerous studies have been done on the mechanical behavior of the various new joints. In this paper, a new DDCI connector for the shield tunnel joint was proposed. Simultaneously, a thermo-mechanical performance analysis was conducted on the new longitudinal joint combining inclined bolts and the DDCI connector. A refined finite element model of the new joint was established and various working conditions were designed to obtain a full understanding of the thermo-mechanical performance of the structure. This evaluation included the presence of initial loads and exposure to different fire curves, specifically the RABT and RWS fire curves. The validity of the numerical model and the indirect coupling analysis method were verified by physical experiments and previous research, respectively. The temperature distribution, joint opening and internal force of the connectors were analyzed in the study. According to the results, different fire curves and thermo-mechanical sequences both have a great impact on the mechanical response of the new joint under elevated temperature. Moreover, due to the involvement of the DDCI connector, the new joint shows clear advantages in strength and stiffness over the conventional joint. The results contribute to the fire-resistant design of the large-diameter shield tunnels adopting the scheme of the new joint with a DDCI connector.

Longitudinal structural resilience of shield tunnel: Characterization and field application

The longitudinal structural resilience performance of shield tunnels is an important concern given the dramatic development of underground systems and the increasing demand for maintenance work. In this paper, a new model using longitudinal relative differential settlement as the index of tunnel structural resilience performance is proposed. The resilience metric (Re) is defined as the ratio of the area integrated by the residual performance during environmental disruptions to the area integrated by the normal performance for the corresponding duration. Then, the proposed resilience analysis model is applied to a well-documented case in Shanghai, where the existing metro tunnel is disrupted by a newly constructed large-diameter shield tunnel undercrossing and subsequently repaired by soil grouting. The variations of tunnel settlement concerning construction parameters and driving distance of the shield machine are analyzed. The performance degradation characteristics of the tunnel during disruption and recovery are effectively captured. The results show that 32.3 % of the performance loss is attributed to the new tunnel undercrossing in the first 38 days. After the completion of the grouting reinforcement, the tunnel performance is improved from 0.677 to 0.868, accounting for approximately 59.1 % of the performance loss during the crossing period. Moreover, the resilience metric (Re) is calculated as 0.764, indicating a high level of resilience for the existing metro tunnel in this case. In addition, other performance indexes based on tunnel longitudinal settlement are discussed, demonstrating the good rationality and applicability of the proposed index.

Disaster mechanism of large-diameter shield tunnel segments under multi-source load coupling: A case study

The deflection squeezing of the shield shell and the eccentric jack thrust significantly impact the segment dislocation and damage. Based on summarizing the derivative relationship between engineering factors and disasters, this study established a 3D numerical calculation model under the multi-source load coupling. Then, this study explored the displacement and dislocation distribution of segments, as well as their derivative relationship with bolt failure. Furthermore, this study analyzed the spatial distribution and evolution characteristics of segment damage. Further revealing the disaster mechanism and proposing the engineering treatment measures. The research results indicate that as the deflection angle increases, the vertical relative compression deformation of the segment that is detaching from the shield tail (segment-DFST) becomes more significant. The plastic strain of the internal bolts inside the two segments in direct contact with the shield shell is mainly related to the radial and longitudinal dislocation. The increase in the deflection angle will lead to a more significant increase in the adjacent dislocation on both sides and the internal dislocation. The plastic strain of the internal bolts of the segment that is completely in the shield shell (segment-CSS) is more influenced by joint opening and longitudinal dislocation under the lower eccentric compression (LEC) state. The plastic strain of the internal bolts in segment-DFST is more influenced by radial dislocation and joint opening under the LEC state. The tension damage of the segments mainly occurs on both sides of the circumferential joint and the lower part of the segment-CSS. The compression damage of the segments is mainly distributed at the top and bottom of the segment-CSS. The eccentric distribution of jack thrust has the most significant impact on the block damage of the lower part of the segment-CSS. With the increase of the deflection angle, the compression damage and distribution range of the blocks at the bottom of the segment-DFST increase sharply. The compression damage and distribution range of the segment-CSS gradually spread from the upper and lower parts to the middle of the segment. The increase in deflection angle will promote the influence of the thrust in LEC state on the compression damage of the lower block of the segment-CSS, and on the tension damage of the upper block of the segment- DFST.

Physical and mechanical response of large-diameter shield tunnel lining structure under non-uniform fire: A full-scale fire test-based study

When a fire occurs in an underground shield tunnel, it can result in substantial property damage and cause permanent harm to the tunnel lining structure. This is especially true for large-diameter shield tunnels that have numerous segments and joints, and are exposed to specific fire conditions in certain areas. This paper constructs a full-scale shield tunnel fire test platform and conducts a non-uniform fire test using the lining system of a three-ring large-diameter shield tunnel with an inner diameter of 10.5 m. Based on the tests, the temperature field distribution, high-temperature bursting, cracking phenomena, and deformation under fire conditions are observed. Furthermore, the post-fire damage forms of tunnel lining structures are obtained through the post-fire ultimate loading test, and the corresponding mechanism is explained. The test results illustrate that the radial and circumferential distribution of internal temperature within the tunnel lining, as well as the radial temperature gradient distribution on the inner surface of the lining, have non-uniform distribution characteristics. As a result, the macroscopic phenomena of lining concrete bursting and crack development during the fire test mainly occur near the fire source, where the temperature rise gradient is the highest. In addition, the lining structure has a deformation characteristic of local outward expansion and cannot recover after the fire load is removed. The ultimate form of damage after the fire is dominated by crush damage from the inside out of the lining joints in the fire-exposed area. The above results serve as a foundation for future tunnel fire safety design and evaluation.

Research and Applications of FRP in Large-Diameter Shield Tunnel Engineering

Research and Applications of FRP in Large-Diameter Shield Tunnel Engineering

Large-diameter shield tunnel crossing closely to existing metro tunnels and a residential building: A case study

In urban regions with multiple existing underground structures, the construction of a new shield tunnel can elicit intricate responses in soil-structure interactions. Here, we present an exhaustive case study of a large-diameter shield tunnel project in Shanghai, focusing on the section that closely crosses an existing metro tunnel and a residential building. Based on the in-situ data, the settlements of the ground, metro tunnel, and residual building induced by the tunneling were analyzed, and the correlations of their deformation mechanisms were discussed. The results indicate that the presence of a metro tunnel effectively mitigates ground movement. The settlement near the existing metro tunnel is significantly smaller than that in relatively remote areas. Additional displacements, settlements followed by heaves, were observed in the existing metro tunnels. Tunneling-induced settlement was also observed in the residential building, reaching a maximum of 8.92 mm facing the crossing side. Settlement along the tunneling direction decreased notably for residential buildings, primarily owing to the reinforcing effect of the existing metro tunnel. These findings underscore the importance of considering the soil-structure interaction within multiple existing underground structures during close tunnel crossings.

A resilience optimization design model considering surcharge for large diameter shield tunnel

Large-diameter shield tunnels face challenges owing to the complex strata and surcharges. The robustness of ground disturbance during excavation and resilience during operation in the design model must be considered. This involves establishing a damage evolution law for existing shield tunnels after surcharging and proposing a resilience design method for the entire cycle. In this study, the design process was initiated by utilizing existing borehole survey information and incorporating stratum uncertainty. Subsequently, a ground surcharge was applied to evaluate the changes in the force and deformation at different design points after surcharging. A resilience assessment was conducted in accordance with the specified criteria, and the results indicated that a majority of the design points exhibited robustness within acceptable limits after the surcharge. The original excavation design demonstrated satisfactory initial performance in terms of robustness. However, the resilience after surcharging was suboptimal, exhibiting a value of only 0.65. To enhance the resilience, the design must modify the reinforcing rate to achieve a higher resilience state of 0.8. By considering both the robustness of the design and its resilience after surcharging, modifications can be made to align the design with real operational conditions, which may help improve the overall resilience.

Influence of secondary lining thickness on mechanical behaviours of double-layer lining in large-diameter shield tunnels

In large-diameter shield tunnels, applying the double-layer lining structure can improve the load-bearing properties and maintain the stability of segmental lining. The secondary lining thickness is a key parameter in the design of a double lining structure, which is worth being explored. Based on an actual large-diameter shield tunnel, loading model tests are carried out to investigate the effect of the secondary lining thickness on the mechanical behaviours of the double lining structure. The test results show that within the range of secondary lining thicknesses discussed, the load-bearing limit of the double-layer lining increases with growing secondary lining thickness. As a passive support, the secondary lining acts as an auxiliary load-bearing structure by contacting the segment. And changes in secondary lining thickness have a significant effect on the contact state between the segment and secondary lining, with both the contact pressure level and the contact area between the two varying. For double-layer lining structures in large-diameter shield tunnels, it is proposed that the stiffness of the secondary lining needs to be matched to the stiffness of the segment, as this allows them to have a coordinated deformation and a good joint load-bearing effect.

Limit equilibrium models for passive failure of a large-diameter shield tunnel face in reinforced soft clay

Limit equilibrium models for passive failure of a large-diameter shield tunnel face in reinforced soft clay

Influence and the Control of Shield Tunneling on Ancient Tower Vibration

In recent years, to effectively mitigate the issue of urban traffic congestion, tunnels have become widely used new type of road. However, when the soil layer is excavated and disturbed, the resulting vibration affects the safety of the buildings above it, especially for ancient buildings that are very sensitive to vibrations. Taking the White Tower in Hangzhou as an example, in this paper, the vibration response propagation of large-diameter shield tunnel excavation to adjacent ancient towers is studied through field measurements. The vibration response of the unexcavated south line tunnel is predicted by using 3D numerical analysis software, and the optimal construction parameters are obtained. The study found that the frequency domain component of the White Tower bedrock vibration caused by shield tunneling is mainly 5–20 Hz, and the vibration response attenuates significantly beyond 40 m. Further, reducing the propulsive force can reduce the vibration response of the White Tower; therefore, controlling the propulsion and reducing the tunneling velocity can reduce the vibration response.

Disaster mechanism analysis for segments floating of large-diameter shield tunnel construction in the water-rich strata: A case study

During the construction of large-diameter shield tunnels crossing water-rich strata near the sea, serious disasters such as segment floating, cracking, and water leakage often occur. This study, based on field tests, identified the engineering disaster factors of segment floating and adjacent misalignment, established a numerical calculation model for shield tunnel construction considering the interaction between segments, revealed the engineering disaster derivation mechanism in the water-rich environment, proposed treatment measures for engineering disaster, and the effectiveness of the treatment measures were verified in field engineering. The research results indicate that the larger grouting pressure in the lower part of the segment will cause greater compression deformation along the radial direction, leading to greater adjacent misalignment and more obvious circumferential rotation of the segment, significantly increasing the risk of local yielding of bolts and reinforcement mesh. At the beginning of grouting, the flow velocity of pore water in the strata is the highest, and as the grout around the segment gradually solidifies, the flow velocity and accumulation range of pore water around the segment gradually decrease. The optimal grout material ratio including 200 kg of cement, 380 kg of water, 680 kg of sand, 380 kg of fly ash, and 90 kg of bentonite can effectively limit the floating displacement of the segment, and improve the assembly flatness of segment along the longitudinal direction.

Real-time deformation monitoring of large diameter shield tunnel based on multi-sensor data fusion technique

The measurement of the shield tunnel deformation is an important tool to ensure structural integrity. The structural “deformation” of the tunnel is not merely a simple geometric deformation, which includes the elastic deformation of the segments and the rigid deformation caused by the opening and misalignment of the joints between the segments. Therefore, it is hard to monitor the deformation only relying on a single device. In this study, a data-fusion computing algorithm based on a fusion of rotation and strain measurements is proposed to improve the accuracy of tunnel deformation monitoring without the need of reference frame. SmartRock sensor was utilized to record rotation and the strain change of tunnel segments. Kalman filter was used as the fusion technique. The algorithm was successfully applied in the project of Jinan Yellow River tunnel, China. The result was compared with the result obtained by laser scanner and shows good consistency.

The mechanical deformation characteristics of the internal structure of large diameter shield tunnel in different construction stages

PurposeUnder the repeated action of the construction load, opening deformation and disturbed deformation occurred at the precast box culvert joints of the shield tunnel. The objective of this paper is to investigate the effect of construction vehicle loading on the mechanical deformation characteristics of the internal structure of a large-diameter shield tunnel during the entire construction period.Design/methodology/approachThe structural response of the prefabricated internal structure under heavy construction vehicle loads at four different construction stages (prefabricated box culvert installation, curved lining cast-in-place, lane slab installation and pavement structure casting) was analyzed through field tests and ABAQUS (finite element analysis software) numerical simulation.FindingsHeavy construction vehicles can cause significant mechanical impacts on the internal structure, as the construction phase progresses, the integrity of the internal structure with the tunnel section increases. The vertical and horizontal deformation of the internal structure is significantly reduced, and the overall stress level of the internal structure is reduced. The bolts connecting the precast box culvert have the maximum stress at the initial stage of construction, as the construction proceeds the stress distribution among the bolts gradually becomes uniform.Originality/valueThis study can provide a reference for the design model, theoretical analysis and construction technology of the internal structure during the construction of large-diameter tunnel projects.

Prediction of surface settlement caused by synchronous grouting during shield tunneling in coarse-grained soils: A combined FEM and machine learning approach

This paper presents a surrogate modeling approach for predicting ground surface settlement caused by synchronous grouting during shield tunneling process. The proposed method combines finite element simulations with machine learning algorithms and introduces an intelligent optimization algorithm to invert geological parameters and synchronous grouting variables, thereby predicting ground surface settlement without conducting numerous finite element analyses. Two surrogate models based on the random forest algorithm are established. The first is a parameter inversion surrogate model that combines an artificial fish swarm algorithm with random forest, taking into account the actual number and distribution of complex soil layers. The second model predicts surface settlement during synchronous grouting by employing actual cover-diameter ratio, inverted soil parameters, and grouting variables. To avoid changes to input parameters caused by the number of overlying soil layers, the dataset of this model is generated by the finite element model of the homogeneous soil layer. The surrogate modeling approach is validated by the case history of a large-diameter shield tunnel in Beijing, providing an alternative to numerical computation that can efficiently predict surface settlement with acceptable accuracy.

Study on the Applicability of Load Calculation Method for Large-Diameter Shield Tunnel in Argillaceous Sandstone Stratum under High Water Pressure

Surrounding rock pressure is an important factor to be considered during designing tunnel structures. In this research, the on-site surrounding rock pressure of a large diameter shield tunnel in argillaceous sandstone stratum was tested, and the evolution process of surrounding rock pressure was analyzed, based on which the variation law of surrounding rock pressure with buried depth and span of the tunnel was discussed. Combined with the numerical simulation method, the applicability of the load calculation method for the large-diameter shield tunnel in the argillaceous sandstone stratum was studied. The results showed that the variation of surrounding rock pressure generally changed from a rapid and substantial increase to a slight decrease and finally tended to be stable. Before reaching stability, the deformation pressure was dominant; then, the loosening pressure became the main pressure, and the surrounding rock pressure almost reached the maximum value in the synchronous grouting stage. Moreover, it was also found that the shield construction had a great influence on the surrounding rock pressure of the 15-ring segments behind the working face. While calculating the surrounding rock pressure, the tunnel section shape, buried depth and surrounding rock conditions should be fully considered. The Full Soil Column Theory, Terzaghi's Theory, Xie's Theory and Bierbauman's Theory were more suitable for tunnels with a buried depth of less than 2.5 hp. When the buried depth of the tunnel exceeded 2.5 hp, the calculation results needed to be enlarged by 2 ∼ 3 times if the Statistical Method or Protodyakonov's Theory was used for calculation. Xie's Theory can be used to calculate the surrounding rock pressure of shallowly buried argillaceous sandstone stratum large-diameter shield tunnel. For a deeply buried argillaceous sandstone stratum large-diameter shield tunnel, it is recommended to use Numerical Simulation Method.

Research on the effect of double sealing gaskets arrangement on the mechanical behavior of the segment longitudinal joints with large diameter shield tunnel

The sealing gasket of the traditional double waterproof system of the large diameter shield tunnel consists of two sealing gaskets which are arranged on the outside of the bolt hole(SGOH) or arranged on both sides of the bolt hole(SGBH). The different arrangement of the double sealing gaskets has significant effects on the mechanical behaviors of the longitudinal joints of the segment. In this paper, based on the energy equivalence principle, the actual distribution stress of the compression zone of the segment longitudinal joints was simplified equivalently as rectangular distribution stress. Then, a progressive mechanical model was established for the longitudinal joint, taking into account the effect of double sealing gaskets arrangements. Furthermore, the proposed mechanical model was validated through former experimental results and other analytical models. Finally, the effect of different arrangements of the double sealing gaskets on the mechanical behavior of the longitudinal joints of the segment was compared and analyzed. The results showed that the difference in the arrangement of the double sealing gaskets results in varying effects of the additional bending moment on the joint bending deformation under sagging and hogging moments, leading to the unequal bending stiffness of the joint. The difference in bending stiffness caused by the double sealing gasket arrangements is approximately 100∼150 MN·m/rad. To optimize the mechanical behaviors of the joints, the double sealing gaskets should be arranged on both sides of the bolt hole(SGBH), with the bolt located at the center of both the longitudinal joints and the core compressive zone of the longitudinal joints.

Improved equations of ground pressure for shallow large-diameter shield tunnel considering multiple impact factors

Reasonable estimation of ground pressure is of vital importance for lining segments design in shield tunnelling. With the rapid development of the urban transportation, the diameter of the shield tunnel tends to become larger. The existing prediction of the ground pressure may overestimate the ground pressure of the shallow large-diameter shield tunnel and thus produce higher cost for the shield tunnel construction. To provide more reasonable solution for ground pressure surrounding the shallow large-diameter shield tunnel, a series of improved equations are proposed in this study. The two-stage method with non-uniform displacement pattern through numerical modelling is used to simulate the shield tunnelling at first. Secondly, the effect of multiple impact factors on horizontal and vertical ground pressure at tunnel vault, haunch and invert is analyzed and five key impact factors are determined. Thirdly, a series of improved equations are presented based on a large number of numerical modelling through nonlinear regression analysis. These improved equations can consider the effect of multiple impact factors and predict the ground pressure varying with position which is more realistic for the shallow large-diameter shield tunnel. Therefore, when compared with both the numerical modelling results and field measurements for 70 case histories, the improved equations show good performance. Also, the ground pressure of the above cases is calculated by traditional methods such as overburden pressure, Protodiaconov's formula and so on. By contrast to 7 traditional methods, the improved equations predict more reasonable result of ground pressure. At last, the influence of the tunnel axis depth, tunnel diameter, GAP parameter, ground classification and in-situ coefficient of lateral pressure at rest on the vertical ground pressure at tunnel vault is investigated through the improved equations. The results indicate that the tunnel size is of significant importance to the ground pressure as expected and thus special attention should be paid to shallow large-diameter shield tunnel. However, engineers may save the cost when tunnel diameter outweighs 15 m as ground pressure varies insignificantly. Furthermore, the initial stress as well as the GAP parameter which represents the shield tunnel construction details also play a vital role in ground pressure.

Seismic damage characteristics of large-diameter shield tunnel lining under extreme-intensity earthquake

This paper investigates the damage pattern of the concrete lining in a large-diameter subsea shield tunnel under different seismic loading intensities. Based on the Shantou Bay (STB) Tunnel, a refined finite element (FE) model consisting of “1/2 + 1+1/2” liner-rings is established in the study. In addition, another FE model considering both the strata and lining is created to obtain the seismic displacement-time history, which is employed as the boundary conditions on the “1/2 + 1+1/2” liner-rings model. A whole-ring model is thereafter generated considering the segment details, adopting the Concrete Damage Plastic (CDP) constitutive assumption and artificial viscoelastic boundary. An improved reaction-displacement method based on the concept of the “equivalent layer” is proposed to consider stratum-structure interaction. Finally, two types of seismic intensities and three work conditions are employed to investigate the influence on lining segments and joint openings. The results show that: (i) the damage to the segment of the shield tunnel is mainly concentrated in the top and bottom of the arch and the outer area of the waist under seismic loading; (ii) the moment of a sudden change in the damage development trend and the joint opening is related to the peak response of seismic time history; (iii) the segments of the shield tunnel are dominated by vertical oval shape deformation under a horizontal earthquake, and dominated by horizontal oval shape deformation under a vertical earthquake; (iv) the area and level of lining damage increase with the development of the earthquake intensity.

Analysis of Microtremor Exploration Application and Construction Monitoring in a Large-Diameter Shield Tunnel

In recent years, shield tunneling has shown many advantages with the development of underground rail traffic. Geological exploration plays a significant role in tunnel engineering, and detailed geological exploration results can guide the successful construction of a tunnel. This research relies on a super large-diameter shield tunnel construction, using microtremor exploration technology to collect data onsite. Combined with a comparative analysis of the borehole surveying, the reliability of microtremor exploration technology is verified. Moreover, the monitoring result of the impact of large-diameter slurry balanced shield construction on the surrounding environment is analyzed. The results show that microtremor exploration can obtain geological details that traditional detection methods cannot obtain, which can predict the possible local geology mutation in front of the tunnel in advance. The law of surface settlement curve conforms to the Peck formula. This can be divided into five stages: micro deformation, extrusion uplift, reciprocating uplift, detachment settlement, and consolidation settlement. The surface settlement on the eccentric loads side is more prominent. The maximum pressure outside the tunnel segment appears on the lower side of the monitoring section, approximately 0.41 MPa, which will increase with the grouting pressure and become stable in five days.

Study on the Effects of Artificial Trapezoidal Freezing Soil Mass on the Stability of Large-Diameter Shield Tunnel Portal

The shield tunnel end reinforcement is important in the water-rich sandy strata. In this paper, a trapezoidal freezing soil mass was proposed to reinforce the shield tunnel end, and the reinforcement effects were evaluated based on the Wuhu River-Crossing Tunnel. Firstly, the influences of the freezing soil mass geometric dimensions on the stability of the tunnel portal were analyzed. Then, displacements of the tunnel portal with different trapezoidal freezing soil masses were simulated. Finally, the trapezoidal freezing soil mass was applied in the Wuhu River-Crossing Tunnel. The results show that the portal’s stability is improved significantly with increased freezing soil mass longitudinal length if the length is less than the tunnel diameter. The lower side of the trapezoidal freezing soil mass has a greater influence on the tunnel portal stability than the upper side. The trapezoidal freezing soil mass is more effective than the rectangular freezing soil mass for the Wuhu River-Crossing Tunnel end reinforcement. The trapezoidal freezing soil mass is a good choice for the shield tunnel end soil reinforcement in water-rich sandy strata. This study provides a freezing reinforcement method for the large-diameter shield tunnel end, which provides guidelines for similar engineering.