Expanded Longitudinal Deformation Profile in Tunnel Excavations Considering Rock Mass Conditions via 3D Numerical Analyses (original) (raw)
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Improved Longitudinal Displacement Profiles for Convergence Confinement Analysis of Deep Tunnels
Rock Mechanics and Rock Engineering, 2009
Convergence-confinement analysis for tunneling is a standard approach for preliminary analysis of anticipated wall deformation and support design in squeezing ground. Whether this analysis is performed using analytical (closed form) solutions or with plane strain numerical models, a longitudinal displacement profile (LDP) is required to relate tunnel wall deformations at successive stages in the analysis to the actual physical location along the tunnel axis. This paper presents a new and robust formulation for the LDP calculation that takes into account the significant influence of ultimate (maximum) plastic radius. Even after all parameters are appropriately normalized, the LDP function varies with the size of the ultimate plastic zone. Larger yield zones take a relatively longer normalized distance to develop, requiring an appropriately calculated LDP. Failure to use the appropriate LDP can result in significant errors in the specification of appropriate installation distance (from the face) for tunnel support systems. Such errors are likely to result in failure of the temporary support. The equations presented here are readily incorporated into analytical solutions and a graphical template is provided for use with numerical modeling.
Computers and Geotechnics, 2020
Rock mass behaviour model selection, in particular, to represent the post-failure behaviour and timedependent behaviour of rock masses, are critical issues in the correct application of tunnelling design techniques such as the convergence-confinement method or numerical modelling. This study provides a general numerical approach for predicting longitudinal deformation profiles using a coupled ViscoElastic-ViscoPlastic Strain-Softening (VEVP-SS) model. A viscous dashpot and the strain-softening model are coupled to simulate the progressive damage process and creep failure behaviour of rock masses. Different failure criteria are considered to simulate the post-failure behaviour. As a verification step, numerical creep tests are carried out to analyse the coupled behaviour, and the basic viscoelastic and strain-softening results of the VEVP-SS model are compared with analytical solutions and numerical results. The proposed method is able to consider the coupling between post-failure behaviour and time-dependent behaviour, thus providing a new alternative method for preliminary tunnel design. Parametric analyses are then carried out to investigate the influence of different aspects on the longitudinal deformation profiles. The tunnel deformation based on the VEVP-SS model is larger than the corresponding elastic-plastic results due to the contribution of the creep behaviour, and the excavation rate becomes relevant when considering timedependent behaviour.
Extending the Convergence Confinement Method to Study the Role of the Face In Tunnel Stability
The Convergence Confinement Method (CCM) is a 2D simplified approach for resolving 3D rock-support interaction problems associated with the installation of support near a tunnel face in underground excavations. Some authors have recently put forward the idea that the behaviour of the face played a very relevant role in tunnel stability, so some new approaches to tunnel design and construction are appearing based on the study of the tunnel face. Apparently, the CCM cannot analyse these topics. However, the authors have observed that there is a relationship between the behaviour of a tunnel section and the behaviour of the tunnel face.
Tunnelling and Underground Space Technology, 2012
We describe techniques to estimate plastic radii and longitudinal deformation profiles of tunnels excavated in rock masses. The longitudinal deformation profile, a graph that relates a fictitious internal pressure to the distance to the tunnel face, is necessary to assess adequate distance to the face for the purpose of installing support. Traditional application of this method usually relies on an elastic representation of the longitudinal deformation profile. A more realistic approach has been proposed recently that accounts for the elastoplastic nature of rock masses. It is based, however, on assuming elastic-perfectly plastic rock mass behaviour, an assumption which is more or less realistic, but only for low quality rock masses with a geological strength index (GSI) below 35. We extend this approach to the case of strain-softening rock masses representing a wider range of rock masses (25 < GSI < 75). Based on studying various numerical techniques to estimate these curves, we propose a simplified approximate equation of the plastic radius of a tunnel excavated in a strain-softening rock mass, which can be combined with existing longitudinal deformation profile estimation techniques to analytically obtain a more realistic approach to calculating longitudinal deformation profiles for strain-softening rock masses.
Interpretation of displacement monitoring data for tunnels in heterogeneous rock masses
International Journal of Rock Mechanics and Mining Sciences, 2004
The introduction of geodetic methods to measure absolute displacements in tunnels has improved the value of the data significantly. Structurally controlled behaviour and influences of anisotropy can be determined and the excavation and support adjusted accordingly. In heterogeneous rock masses, a reliable prediction of the conditions ahead of and outside the tunnel profile is of paramount importance for the choice of appropriate excavation and support methods. The increased information contained in the acquired data allows a more comprehensive evaluation of the displacements. The use of advanced methods such as the evaluation of displacement vector orientations on tunnel sites in Austria showed that changing rock mass conditions ahead of the tunnel face can be indicated. The combination of such methods with new developed software for the prediction of displacements in a plane perpendicular to the tunnel axis (GeoFit®) allows the detection of deviations from 'normal' system behaviour in time.
Reducing deformation effect of tunnel with Non-Deformable Support System by Jointed Rock Mass Model
Numerical modeling has been used widely in mining and construction industries in recent years. The most important issue in engineering projects designed with numerical modeling is accurate modeling of rock mass behavior. If the rock mass behavior is modeled accurately, fewer problems will be faced during field application of projects. Selection of the true material model is a very important issue in numerical modeling for the tunnel projects. Non-Deformable Support System (NDSS), which will be mentioned in the scope of this research, does not mean that it does not permit any deformation or is a very stiff system. NDSS is a support system that does not permit deformations exceeding specified deformation amounts which are calculated with determination of the accurate rock mass behavior by the true material model and it must be evaluated with support system and excavation advance specifically. The origin of the paper is that numerical modeling provides more comfortable results in tunneling in case one can determine rock mass deformation and failure behavior appropriately. In (NDSS), however, support system element can only be determined by proper numerical modeling analysis. Moreover, deformation values determined by NDSS analysis are accepted as limit values. Therefore, applied support system should be within deformation tolerance limits determined by NDSS analysis. Briefly, this paper is related to NDSS that should be determined by numerical modeling analysis. In this research, in regard to the excessive deformations in T-35 tunnel which is one of the 33 tunnels of Ankara–Istanbul High-Speed Railway Project, results of the in situ measurements in the tunnel excavated with the new developed NDSS and results of the numerical model made with Jointed Rock Mass Model have been compared. It is determined that the results of the numerical modeling and the in situ measurements are very consistent with each other.
2024
With the advancement of numerical modeling, predicting tunnels' behavior before construction has become possible for designers. Accurate prediction of tunnels' behavior in diverse environments requires the compatibility of numerical simulations with ground conditions. Although several constitutive models have been proposed for simulating ground characteristics, their appropriate utilization is crucial. In this study, the convergence of a tunnel is modeled, and the results are verified using actual convergence monitoring data. Then, a series of finite element simulations are conducted on a hypothetical TBM tunnel to demonstrate the difference in deformations, ground surface settlements, and stresses in the lining resulting from tunnel excavation under seven constitutive models in rock media. The models are categorized into four groups: rock-specified, soil-established, and general. Additionally, parametric studies are performed on specific gravity, Poisson's ratio, and dilation angle. The findings revealed that different constitutive models significantly influence numerical analysis results. Rockspecified models were found to be more sensitive to parameter variation in rock media than soil-established and general models. Moreover, changes in specific gravity and Poisson's ratio had a significant impact on the magnitude of surface settlements. Overall, the study highlights the importance of appropriately selecting constitutive models and accurately defining material parameters in numerical simulations to ensure reliable predictions of tunnel behavior.
Tunnelling and Underground …, 2012
Design of Sequential Excavation Method (SEM) and its support system in weathered and incompetent rocks is a primary challenge in tunneling. The Shibli tunnels that are being constructed within Zanjan-Tabriz freeway are located 25 km away from Tabriz with total length of 4533 m (north tunnel: 2244 m, south tunnel: 2289 m), 14 m width, and 11 m height. Three collapses that occurred at initial 800 m length of southern tunnel necessitated modification of either or both of the support system or excavation sequences. In this study, modification of the excavation sequences was merely taken into consideration for the high costs required to change the support system. Initially, the method of top heading and benching was proposed based on size of tunnels span and the ratio of Uniaxial Compressive Strength (UCS) to vertical in situ stress. Subsequently the excavation sequences were examined and designed precisely. Application of back analysis technique on three aforementioned collapsed zones led to identification of the most probable rock mass shear strength parameters. Results obtained from this analysis showed that in crown part of collapsed zones the displacement values had laid in an interval between 70 and 75 mm. Therefore, based on the weakest strength parameters obtained from the back analysis, three different sequences of excavation were proposed and sent to a finite difference numerical modeling which followed by an efficient SEM design with safety factor of 2 that reduced the displacements after excavation of top heading and whole tunnel section in the collapsed zones to less than 45 mm and 70 mm respectively. Thereafter, the modified SEM design has been applied successfully without occurrence of further collapses throughout excavation of the remained length of Shibli tunnels.