Effect of Boundary Conditions in Segmental Lining Model on its Sectional Force

Song J., Miao L., Feng S.

Li Z., Soga K., Wang F., Wright P., Tsuno K.

The behaviour of cast-iron tunnel segments used in London Underground tunnels was investigated using the 3-D finite element (FE) method. A numerical model of the structural details of cast-iron segmental joints such as bolts, panel and flanges was developed and its performance was validated against a set of full-scale tests. Using the verified model, the influence of structural features such as caulking groove and bolt pretension was examined for both rotational and shear loading conditions. Since such detailed modelling of bolts increases the computational time when a full scale segmental tunnel is analysed, it is proposed to replace the bolt model to a set of spring models. The parameters for the bolt-spring models, which consider the geometry and material properties of the bolt, are proposed. The performance of the combined bolt-spring and solid segmental models are evaluated against a more conventional shell-spring model.

Do N., Dias D., Oreste P., Djeran-Maigre I.

The main purpose of this study was to provide a three-dimensional numerical model, which would allow the tunnel lining behaviour and the displacement field surrounding the tunnel to be evaluated. Most of the processes that occur during mechanized excavation have been simulated in this model. The influence of the lining joint pattern, including segmental lining joints and their connections, has in particular been taken into consideration. The impact of the processes during mechanized excavation, such as the grouting pressure and the jacking forces in the structural forces induced in the tunnel lining, has been presented. These values depend on the tunnel advancement. However, a negligible influence of the joint pattern on the ground displacement field surrounding the tunnel has been observed. Generally, a variation in the structural forces in successive rings along the tunnel axis has been found in a staggered segmental lining, indicating the necessity of simulating the joints in the tunnel lining and using a full three-dimensional numerical model to obtain an accurate estimation. In addition, the considerable influence of the coupling effect between successive rings on the lining behaviour has been highlighted.

Do N., Dias D., Oreste P., Djeran-Maigre I.

The application field of shield tunneling has extended in recent years. Most shield-driven tunnels are supported by segmental concrete linings. Although many well documented experimental, numerical and analytical results exist in literature concerning the functioning of segmental tunnel linings, their behavior under the influence of joints is still not clear. This paper presents a numerical study that has been performed to investigate the factors that affect segmental tunnel lining behavior. Analyses have been carried out using a two-dimensional finite difference element model. The longitudinal joint between segments in a ring has been simulated through double node connections, with six degrees of freedom, represented by six springs. The proposed model allows the effect of not only the rotational stiffness but also the radial stiffness and the axial stiffness of the longitudinal joints to be taken into consideration. The numerical results show a significant reduction in the bending moment induced in the tunnel lining as the joint number increases. The tunnel behavior in terms of the bending moment considering the effect of joint distribution, when the lateral earth pressure factor K 0 is equal to 0.5, 1.5 and 2, is almost similar and differs when K 0 is equal to unity. It has been seen that the influence of joint rotational stiffness, the reduction in joint rotation stiffness under the negative bending moment, the lateral earth pressure factor and Young’s modulus of ground surrounding the tunnel should not be neglected. On the other hand, the results have also shown an insignificant influence of the axial and radial stiffness of the joints on segmental tunnel lining behavior.

Chakeri H., Ozcelik Y., Unver B.

Due to population growth, people demand more and more transportation services, there can be no doubt that the requirement for tunnels will also grow. Mechanized excavations using EPB have been successfully applied, especially in urban environments where there is less surface space available, over the past twenty years. Because of excavation speed and less hazardous working environments, use of the Earth Pressure Balance Machine (EPB) is a more popular method in metro, railway and road tunnels in urban areas. Control of surface settlement is very important when tunnels are excavated in urban areas or beneath important structures. This research mainly discusses effects of important properties like tunnel depth, overburden pressure, tunnel dimension and face pressure using empirical, theoretical and numerical methods used to control surface settlement. Results of these methods are compared with observation data.

Dias D., Kastner R.

In this paper, monitoring results of two cross tunnel sections are presented. This underground work has been realized for a subway in an urban area (Lyon, France). By comparison with measurements of other projects, it appears that the face instability and the annular gap identified after the shield release are the main sources of short-term settlements. These observations of vertical and horizontal movements during the tunnel excavation by a slurry pressurized tunnel boring machine are then compared with several numerical approaches. The 2D numerical approach uses the concept of volume loss and is applied to each excavation stage. It simulates approximately the observed movements but requires the use of empirical coefficients to represent in two dimensions the three-dimensional problem. The 3D approach considers more directly the physics of the problem and permits to take into account: the slurry pressure at the tunnel face, the shield conicity, the grout injection in the annular void and the grout consolidation. Three dimensional numerical calculations are the most accurate approaches to simulate all the physical processes occurring during tunneling. However this type of model assumes that all the parameters that control the movements induced by the excavation are well known. Due to the complexity of a tunneling boring machine, it is not necessarily the case.

Arnau O., Molins C.

The particular configuration of segmental tunnel linings produces that its structural response in front of usual design loads could present a significant three dimensionality due to the structural interaction between adjacent rings (coupling effects). The present paper studies the phenomena associated to coupling effects, determines the main involved parameters and analyzes their influence on a real lining structural response by means of a 3D numerical model. The comparison with the usual plane models currently employed in linings designs provide significant conclusions about the coupling effects implications and the conditions in which become more relevant.

SUGIMOTO M., SRAMOON A., OKAZAKI M.

Teachavorasinskun S., Chub-uppakarn T.

A simplified method for evaluating the moment carrying of a segmental tunnel liner was proposed using a result from a FEM analysis in which parameters were obtained by calibration against a true scale model test. Influence of segmental joint, number of segment and soil subgrade modulus on the bending moment carrying characteristics of a segmental tunnel was examined. Joint was represented by a series of springs called angular joint stiffness. Based on a set of model tests, practical range of angular joint stiffness was in range of 1000–3000 kN m/rad. It was found that jointed lining carried smaller value of maximum bending moment than the non-jointed one. The reduction in bending moment, represented by the parameter called moment reduction factor, can be simply expressed as a function of angular joint stiffness and number segment.

Li Y., Emeriault F., Kastner R., Zhang Z.X.

The face stability of large slurry shield-driven tunnels is investigated by an upper bound approach in limit analysis and three-dimensional numerical modelling for the Shanghai Yangtze River Tunnel. Both the local failure and global failure in collapse and blow-out are studied. Firstly, the upper bound solution for local stability is presented, taking into account the gradient of slurry pressure. The maximum tunnel diameters for given site conditions could be determined by this solution. Then, the progressive global stability mechanism is studied using a multiblock model of upper bound theorem. The analysis shows that it is necessary to take into account the partial failure in large size slurry shield-driven tunnels, especially in the case of blow-out. The global blow-out of the partial upper part of the tunnel face occurs when the slurry pressure is too great; while the global collapse of the whole tunnel face occurs when the slurry pressure is too small. The failure mechanisms and critical slurry pressures obtained from both the multiblock model to numerical simulations are compared with each other.

Klappers C., Grübl F., Ostermeier B.

In contrast to the inner lining of a NATM tunnel the lining of a TBM driven tunnel consists of single precast concrete segments which are articulated or coupled at the longitudinal and circumferential joints. Therefore not only the characteristics of the concrete segments influence the structure but also the mechanical and geometrical characteristics of the joints strongly affect the structural behaviour of the tunnel lining. For the simulation of these joints within the tunnel lining different calculation methods are known. In contrast to the inner lining of a NATM tunnel the lining of a TBM driven tunnel consists of single precast concrete segments which are articulated or coupled at the longitudinal and circumferential joints. Therefore not only the characteristics of the concrete segments influence the structure but also the mechanical and geometrical characteristics of the joints strongly affect the structural behaviour of the tunnel lining. For the simulation of these joints within the tunnel lining different calculation methods are known. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. “Reprinted with permission from Em Elsevier”.

Huang Z., Zhu W., Liang J., Lin J., Jia R.

The most important problem for the design of the shield tunnel linings is whether the design model can reflect the actual stress of the linings. Various methods for the design of segmental tunnel linings are discussed and a new three-dimensional shell-spring design model is put forward. The shell-spring and beam-spring model were used to analysis the sequence and staggered lining arrangement, from which useful guidance for designing the segmental linings can be drawn. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Lee K.M., Hou X.Y., Ge X.W., Tang Y.

This paper presents an analytical solution for the prediction of internal forces and displacements of a jointed segmental precast circular tunnel lining. The effects of joint stiffness on the performance of the tunnel lining are discussed. The ‘force method’ is used to determine the internal forces and displacements of jointed tunnel lining. Five shield-driven tunnel cases are adopted to study the effects of joint stiffness, soil resistance, joint distribution and joint number on the internal forces and displacements of circular tunnels. Laboratory model tests are conducted to verify the proposed analytical solution. Copyright © 2001 John Wiley & Sons, Ltd.

MURAKAMI H., KOIZUMI A.

Pham A.T., Sugimoto M.

The shield tunneling method is widely used, especially in urban areas, since it is efficient for minimizing disturbances to surroundings. Although segmental lining is commonly used in this method, in both the research and practice of tunnel lining design, the interaction between the ground and lining in the tangential direction remains unclear; that is, the mobilizing shear stress due to load models and the degree of the bond in the tangential direction. Therefore, to clarify the effects and mechanism of the tangential ground–lining interaction on segmental lining behavior, a parameter study was carried out, taking tangential spring stiffness, load models, soil stiffness, and shallow and deep tunnels as parameters. The interaction conditions were based on the existing literature. It was found that (1) the tangential spring has small effects on lining behavior, (2) the load model significantly affects the sectional forces, (3) the initial tangential earth pressure and slip ground–lining boundary provide more safety from a design viewpoint, and (4) in the case of shallow tunnels in soft ground, tensile stress appears in the lining. Therefore, it is important to take the tangential ground–lining interaction conditions into consideration during tunnel lining analysis.