Nonlinear Time-Dependent Analysis of the Load-Bearing Capacity of a Single Permanent Shotcrete Lining at the Brenner Base Tunnel (original) (raw)
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Shotcrete is one of the main support elements for tunnels constructed according to the principles of the New Austrian Tunnelling Method (NATM). In this paper, a sophisticated constitutive model for the complex mechanical and time-dependent behaviour of shotcrete is presented, which is formulated within the framework of elasto-plasticity. Two independent yield surfaces govern the material behaviour in compression and tension under multi-axial loading conditions, which is further controlled by non-linear plastic strain hardening and softening rules following uniaxial stress-strain curves. The main novelty of the model is the introduction of normalised hardening and softening parameters which enable a more realistic simulation of the shotcrete loading history. In addition, cracking of the shotcrete is treated within the smeared crack concept by applying a fracture energy approach as a regularisation technique, which eliminates the dependency of the results on the size of the elements in a finite element mesh. Furthermore, the model takes into account the gradual change of the main material properties of the shotcrete due to cement hydration during the first 28 days after spraying. Other important time effects such as creep, shrinkage and hydration temperature induced deformations at early ages are considered in the current model formulation. This paper aims to describe in detail the developed structure of the constitutive model and model calibration.
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2011
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12-13-2018 Multi-Layer Shotcrete Design for Tunnel Construction
2018
Shotcrete is an essential support element for conventionally driven tunnels. Traditionally shotcrete is applied in multiple layers for construction reasons, but for the design the lining is considered as monolithic. This is acceptable, in case the time lag between the application of each shotcrete layer is short, corresponding to one construction step. A different situation occurs, when an additional shotcrete layer is applied with a large delay. In that case the system consists of a pre-loaded and a stress-free layer and needs to be designed accordingly. Currently there is no explicit design procedure incorporated in the design codes, but only recommendations for design, such as relevant codes to be applied and the requirement to consider the pre-loading conditions of the first shotcrete layer. The paper presents and discusses a standard-conform (Eurocode 2) method for design of a concrete cross section consisting of two layers. The method is based on the assumption of full bond between the layers allowing full transfer of shear stress. The design procedure includes the check of strains in the relevant fibres of cross section, i.e. top and bottom fibres of the combined cross section, as well as the interface fibre between the layers. As result a bending momentaxial force interaction diagram of additional bearing capacity of the two layer cross section can be drawn for specific pre-loading conditions of the first shotcrete layer. Parametric study of prestrain conditions of the first shotcrete layer confirmed, that a strengthening of the cross section is reasonable only for cases, when the capacity of the first shotcrete layer is not highly utilized. The additional bearing capacity of a two layer cross section with highly utilized first layer is very limited. 2.
A complex rheological model has been used recently at several Austrian tunnel job sites to determine stresses in a shotcrete lining. The raw data are from displacements measurements at the lining contour. The analysis uses a material model based on a thermo-chemo-mechanical approach. This paper gives a short review of the theoretical background and two case studies. The first one considers a tunnel with top heading/bench and invert excavation and the second one a tunnel with a more complex structure with side galleries and core excavation.
International Journal of Rock Mechanics and Mining Sciences, 2020
An analytical solution is recommended in this paper for time-dependent stress analysis of lined tunnels with a circular shape, regarding tunnel advancing rate. In previous works, it was assumed that the tunnel is excavated under an infinite advancing rate such that the progressing rate effect was neglected, the assumption which is not always true. However, this barrier is removed in this paper. The non-hydrostatic stress field is assumed as initial stress within rock mass. The concrete lining, and surrounding mass are supposed as isotropic homogenous materials, following elastic and viscoelastic constitutive models, respectively. The Burgers model is assumed to dominate viscoelastic behavior. The solution benefits from time discretization for both tunnel advancing rate, and rock support interaction, along with employing complex variable method. The solution presents a good agreement with COMSOL finite element software simulation for different advancing rates. It is found that there exist the progressing rate and time limits, which for higher values, the problem could be solved assuming instantaneous excavation of the hole.
Long-term deterioration of lining in tunnels
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights a b s t r a c t The long-time degradation of sprayed concrete lining in tunnels was studied using three-dimensional finite element method. During the tunnel excavation the rock deformation and forces in the primary shotcrete lining were observed. The gradual degradation of reinforced shotcrete support over a period of time, its perpetual deterioration under the influence of different physical, chemical, mechanical and biological agents and ground pressure was simulated by reduction of the Young′s modulus, cohesion and friction angle to study the impact of this reduction on the stress distribution and overall stability of the tunnel support system consisting of rock mass, shotcrete and the inner lining. Substantiating shotcrete shell deterioration, the progressive increase of stresses in the inner lining and stress dissipation into the surrounding ground was observed. This provided the possibility to illustrate the main attribute of a particular deterioration process on the basis of the obtained stress distributions of the support elements.
Time Dependent Analysis of Tunnels Using The Finite Element Method
Abstract The analyses of tunnels in clay were carried out taking into consideration two great important and effective categories, the time independent and time dependent. Time independent behaviours are used to represent the excavation stage while time dependent analyses are used to represent the behaviour of the unlined tunnel after a long time. The finite element analyses were carried out using the linear elastic model for the concrete liner while elasto-plastic and modified Cam clay model for the soil. The excavation has been used together with transient effects through a fully coupled Biot formulation. All these models and the excavation technique together with Biot consolidation are implemented into finite element computer program named "Modf- CRISP" developed for the purpose of these analyses. In this paper, the basic problem represents the proposed "Baghdad metro line" which consists of two routes of (32 km) long and 36 stations is analyzed. The tunnel is circular in cross section with a (5.9) m outer diameter and (0.45) m of concrete lining thickness. Eight-node isoparametric elements are used to model the soil and concrete lining. Four-node element is used for pore water pressure. Two kinds of analyses are carried out: a- Using elastic-plastic constitutive model for all soil layers. b- Using modified Cam clay model (MCC) for the first soil layer (upper layer) and elastic-plastic Mohr Coulomb for the other two layers. The movements of the soil around the tunnel at the end of excavation at typical points (crown, spring line and the invert) are calculated. The results indicate that there is an inward movement at the crown and this movement is restricted to four and a half tunnel diameters. A limited movement can be noticed at spring line which reaches 0.05% of tunnel diameter, while there is a heave at the region below the invert, which reaches its maximum value of about 0.14% of the diameter and is also restricted to a region extending to (1.5) diameters. It was found that the maximum consolidation settlement above the tunnel is about three times that at the end of excavation. The settlement trough extends only to (5) tunnel diameters using consolidation analysis while it is extended to (12) tunnel diameters using undrained
Performance of Tunnel Lining Materials under Internal Blast Loading
International Journal of Protective Structures, 2014
Performance of different tunnel lining materials under internal blast loading is compared in the present study through three-dimensional nonlinear finite element analyses. A tunnel in sandy soil has been considered for the analyses. The performance of single layered steel plate, plain concrete (PC) slab, steel fibre reinforced concrete (SFRC) slab, sandwich steel-dytherm foam-steel (SDS) panel and steel-polyurethane foam-steel (SPS) panel linings under blast loading have been examined. For material modelling, Drucker-Prager plasticity for soil, Johnson-Cook plasticity for steel, concrete damaged plasticity for concrete, SFRC and crushable-foam plasticity for foams have been used. Strain rate dependent material parameters have been used for all lining materials and soil. Internal blast loading of 10 kg TNT has been simulated using the pressure-time curve obtained through CFD-calculations. The resulting displacements at soil-lining interface have been evaluated. It is observed that SDS and SPS sandwich panel linings cause much less displacement in the soil under blast loading as compared to the PC and SFRC linings.