Structural forces in segmental linings: process-oriented tunnel advance simulations vs. conventional structural analysis

The surrounding soil pressure will significantly impact the existing tunnel lining. To study the deformation characteristics of the staggered segmental tunnel linings structure under this pressure, a model test device considering surrounding soil pressure effects is designed. This device simulates the impact of surrounding soil pressure on staggered lining using special prestressed springs. A bolt connected staggered lining model is also developed. Additionally, concentrated load F simulates loading conditions in some projects, applied to the lining structure. The reliability of test results is validated through numerical simulation. This study investigates segment displacement variations, including tunnel crown vertical displacement Vd, ring and longitudinal joint dislocations CJ and LJ, and convergence deformation C. And the relationship between longitudinal joint dislocation and ring lining deformation. Based on these findings, relationships among vertical displacement, ring joint dislocations, vertical convergence, and longitudinal joint dislocation in the staggered segmental tunnel linings structure are established, offering valuable insights for predicting and analyzing deformation in similar projects.

Circular tunnels are usually encountered when excavation tunnel. However, the U-shapedtunnel lining is used a lot in practice because of it’s advantages. However, there are not many studies inthe world to calculate and design for underground structures with U-shaped tunnel lining, especially inthe case of tunnels being affected by earthquakes. This paper proposes a new numerical-HRM methodapproach for the analysis of U-shaped segmental tunnel lining under the impact of earthquakes. Hanoi isthe capital of Vietnam, this is a big city with more than 8 million people. Hanoi is located between twomajor fault systems, the Red River fault system and the Son La-Dien Bien-Lai Chau fault system.Therefore, the Hanoi area is assessed as likely to be affected by earthquakes of magnitude Mw = 6.1 up to6.5 Richter. The Hanoi metro system is constructed by TBM and the U-shaped segmental tunnel lining isalso one of the types of tunnel lining considered for use in the construction of metro tunnels in Hanoi. Theimproved HRM method has been used to investigate the effect of joints in the tunnel lining from the Hanoisystem metro under the impact of earthquakes is conducted considering from the results of the tunnellining behavior in terms of bending moment (M), normal forces (N) and tunnel lining displacements (δn)in both cases: the U-shaped continuous tunnel lining and the U-shaped segmental tunnel lining.

In tunnel, design of precast tunnel lining are not merely about the strength, but how much its allow to move to account the deflection comes from movement of surrounding soil and load. Thus, the design of tunnel lining is not straight forward. Understanding the flexural behavior of segmented lining is a bonus to optimize design lining in cost effective way. Tunnel lining are designed in segment and have joint that allows tunnel to become flexural and allow deformation taken by the lining load carrying capacity. The objective of this paper is to present some of the research works on segmented tunnel lining conducted in the laboratory. A series of laboratory testing of point load test have been developed to imitate behavior of segmental tunnel lining condition in real. Two types of support system were introduced namely pin-pin and pinroller condition to imitate both rigid and hinge condition of lining. Support mechanisms of pinroller support condition shows variation trend in stress-strain and moment readings and meanwhile for pin-pin it show mirror trend for both result. High stiffness of lining is important at the edge of segment.

Analytical solutions and in-situ measurements on the internal forces of segmental lining produced in the assembling process

Based on Nanjing Yangtze River Tunnel project, the selection of segment lining of large profile underwater shield tunnel was analyzed. Considering from structure force, construction and economic, the comparison and selection for assembling modes, joint form, blocking modes, thickness and width of segment lining was carried out, The better segment lining structure was obtained. The study results can offer references for the design of segment lining of similar large profile underwater shield tunnel.

Sustainability based-approach to determine the concrete type and reinforcement configuration of TBM tunnels linings. Case study: Extension line to Barcelona Airport T1

During an earthquake, the better performance of segmental tunnel lining, compared to the continuous in-cast concrete lining, is generally related to the joints between segments. In order to better understand the influence of the segment joints, their effect on the internal forces induced in tunnel lining simultaneously with the effects of the other influential parameters should be considered. In this work, the segmental joints were simulated by the representative stiffnesses and effects of these characteristics in relation to the other parameters such as the soil-liner interface behavior, number of segments in each ring and thickness of segments on the internal forces induced in structure were investigated. For this purpose, 2D numerical analyses were performed and the results obtained were discussed. Results showed that under the seismic condition, the components that had the most significant role on the internal axial forces induced in the segmental lining were rotational stiffness and axial stiffness of joints. Also the bending moments were more affected by the rotational stiffness. Generally, the radial joint stiffness had a less effect on the induced internal forces. With increase in the number of segments and their thickness, the effect of joint stiffness on the internal forces increases and the design of joints should be given more attention; however, the effects of joint stiffness and frictional behavior at the soil-liner interface on the maximum induced forces are almost independent from each other. Also in a specified joint behavior, by variation in each one of the other parameters including the soil-liner interface condition, number of segments and their thickness, the absolute magnitude of the maximum induced internal forces sometimes change significantly.

The joints between segmental rings can withstand a certain amount of bending moment as well as axial and shear forces. Generally, in the structural analysis of tunnel segmental lining, the joints can be modeled as elastic hinges or rotational springs, and their rigidity should be demonstrated in terms of the rigidity of the joints or their rotational stiffness. Therefore, the bending moment acting on the tunnel lining is reduced. Hence, the tunnel designers are free to choose a lining with a lower cost. In this research work, especially considering the joints, the structural analysis of the segmental lining with variation in the flexural stiffness of the joints ( ), soil resistance coefficient ( ), number of segmental lining joints, and joint arrangement of segmental lining were carried out by the Force-Method equations. The imposed bending moment and axial forces were computed based on the Beam-Spring method, which is widely used to analyze the internal forces of segmental lining, and compared them with the results of the Force-Method equations. Then the effects of joint arrangement patterns and joint rotational spring stiffness on the results of the Beam-Spring analysis were evaluated. Finally, the optimum characteristics of the reinforced concrete segmental lining design were evaluated using the interaction diagram of bending moments and axial forces. The results obtained showed that the presented pattern for the segmental lining at the Chamshir tunnel was imposed against the external pressures on the segmental lining with an acceptable safety factor.

The increasing use of the tunnel boring machines (TBMs) has entailed their own evolution and the improvement of the construction processes applied, allowing the construction of tunnels on more complex hydro-geological conditions. These new drilling facilities imply that higher ground and water pressures have to be resisted by the structural lining, turning its design into a key item in all current tunnel projects. TBMs construction process is mainly associated to precast concrete segmental tunnel linings, which are consisted of concrete rings sequentially placed as the tunnel drilling advances. Despite segmental tunnel linings are widely used, their structural response presents significant uncertainties due to the particular configuration on multiple precast pieces and the evolutionary construction process applied. The improvement and optimization of segmental tunnel linings, necessary to obtain safer structures at a lower cost, requires a significant advance in the knowledge of their structural response and about the appropriate techniques to properly reproduce it. This PhD thesis present the mechanisms and phenomena involved in the structural response of precast concrete segmental tunnel linings, detailing numerical modeling strategies to properly simulate them. The integration of all these techniques in a unique model allows the analysis of a real tunnel lining subjected to different scenarios, determining the influence and relevance of the main parameters defining a tunnel and its structural lining. Present research departs from an innovative in situ test carried out at Line 9 subway tunnel in Barcelona. The treatment and analysis of the obtained data provides experimental evidences about the structural response of segmental tunnel linings and the main involved mechanisms and phenomena. Different numerical simulation strategies are developed in order to properly reproduce such mechanism and phenomena, achieving a reliable simulation of an isolated ring response. The longitudinal response of the segmental concrete linings is obtained through the detailed study of the construction process applied and the ground-structure interaction mechanisms. The knowledge of the longitudinal force present at a segmental tunnel lining is of paramount importance in order to determine the interaction degree between adjacent rings and the consequent three-dimensionality of the lining response. Finally, the numerical simulation of a real tunnel section subjected to different scenarios of load and boundary conditions determines the influence of the three-dimensional effects on segmental concrete linings response, concluding about its structural implications in respect to the isolated ring approach usually employed in design processes.

The prevention and treatment of damage in segmental tunnel lining structures are critical issues in maintaining tunnel integrity. Understanding the damage evolution and failure mechanisms of these structures is essential for their effective management. This study establishes refined numerical models for shield tunnel segmental linings, incorporating critical factors such as localized weakening around hand holes, multi-interface contact behavior, and embedded reinforcement. A total strain crack model is employed to accurately simulate the nonlinear behavior of concrete. The analysis focuses on the compression-bending failure behavior of segmental joints under positive bending moments and investigates the failure mechanisms of segmental linings subjected to surcharge loading. The results show that the deformation of segmental joints under bending moments can be divided into three stages: linear elasticity, elastoplasticity, and failure. The failure mechanism involves the progressive expansion and penetration of cracks in the core pressure-bearing area, leading to increased crack width, yielding of bolts and rebars, and eventual failure. The overall instability failure of segmental tunnel linings is caused by local failures in areas of low stiffness (joints, hand holes), exhibiting progressive failure characteristics. This study presents significant originality and practical value. A refined analytical model of shield tunnel structures is developed to capture the millimeter-scale cracking characteristics of segmental concrete linings. The model enables precise analysis of the mechanical response of shield tunnels under external construction-induced loading.

Despite plenty of research studies in design of segmental tunnel lining, there have still been serious concerns in damage mechanism of segmental lining in weak rock masses. With significant increasing of mechanized tunnelling practically in all kind of ground, including highly weathered rocks, severely jointed rocks, shear, and fault zones, squeezing, and swelling prone conditions, the need to investigate the mechanical behaviour and the damage mechanism of segmental tunnel lining is unavoidable. Any misjudging of those adverse geo-conditions may often cause an irreversible economical loss in the tunnelling project. This paper deals with the significant design aspects of segmental lining for such difficult rock mass conditions which can cause lining deformation and failure in segment in terms of either compression or tension as well as in the segment joints. Further, some critical design aspects extracted from the tunnel T26 of Ankara – Eskisehir high speed railway are presented and analysed.

Investigation of the mechanical properties of double lining structure of shield tunnel with different joint surface

If the serviceability of an existing shield tunnel structure is endangered, strengthening is required. A newly proposed technique of strengthening of segmental tunnel linings, called steel plate – concrete composite structure (SPCCS) strengthening, was experimentally investigated in previous research, in which the tunnel lining was strengthened at the ultimate state. Such a strengthening scheme is denoted as delayed strengthening. Experimental results have shown that the new strengthening technique is advantageous in enhancing the design life of shield tunnels, as compared to traditional strengthening techniques. However, in engineering practice, the tunnel lining must be strengthened before the ultimate state is reached. Hence, the timing of strengthening is a critical parameter in the design of the strengthening process. In the present research, a full-scale test was conducted such that the segmental tunnel lining was strengthened ab initio, i.e. before being subjected to external loading. This mode of strengthening is termed as initial strengthening scheme. The ultimate capacity, the failure process, and the failure mode were investigated. The failure mechanism, the ultimate capacity, the ductility, and the toughness of segmental tunnel linings, reinforced by the SPCCS strengthening technique, were compared with the ones of initial and delayed strengthening schemes. It is shown that the timing of strengthening does not have much influence on the ultimate capacity. However, it has a significant influence on the stiffness, the ductility, and the toughness. The ultimate load bearing capacity of the strengthened structure in case of initial strengthening was found to be only 5.7 % larger than the one in case of delayed strengthening, whereas the increase of the structural stiffness, the ductility, and the toughness is 520.6 %, 46.1 %, and 64.6 %, respectively. Regarding the utilization efficiency of the steel plate, the results have shown that the earlier the structure is strengthened, the greater the utilization efficiency of the strengthening material.

In this study, based on the Jintang Highway submarine shield tunnel project, a precise numerical model for shield tunnels with a secondary lining system is established, integrating the mechanical impacts of bond damage at the interface between segments and secondary linings. From the dual standpoints of tunnel structural safety and applicability, the influence of secondary lining structure types on the load-bearing capacity of the double-layer lining system is systematically examined. The findings reveal that the secondary lining, particularly the enclosed lining scheme, can notably mitigate the internal forces acting on segments and joints, thereby substantially enhancing the safety reserve of the tunnel lining. The non-closed lining structure effectively reduces the internal forces of segmental linings and joints at the arch bottom. The secondary lining itself exhibits an eccentric tensile stress state. Under the non-closed lining scheme, the arch vault, the bottom of the internal structure, and the driveway slab tend to develop penetrating cracks. Compared with the traditional segmental lining, the structural ultimate load-carrying capacity of the enclosed lining scheme, the non-closed lining scheme, and the non-closed lining + flue plate scheme increased by 19.9%, 24.7%, and 30.8% respectively, while the lateral stiffness rose by 24.3%, 89.5%, and 95.4% respectively.

Experimental investigation of seismic performance of segmental tunnel with secondary lining under strong earthquake