Influence of the Tunnel Shape on Shotcrete Lining Stresses

Tunnel excavation is frequently carried out in rock masses by the drill and blast method and the final shape of the tunnel boundary can be irregular due to overbreaks. In order to investigate the effects of overbreaks a study of the effect of tunnel boundary irregularity has been carried out. This is done developing a computational tool able to take into account fuzzy variables (i.e., thickness of the beams of the bedded spring approach used for the model). The obtained results show that irregularity effects should be considered when a shotcrete lining is used as the final tunnel lining (for the case where the tunneling procedure does not permit a smooth surface to be obtained). This is crucial to obtain a durable linin

Numerical Analysis Of Tbm Tunnel Behaviour And Support Under High Stress Rock Masses In Pahang-Selangor Raw Water Transfer Tunnel

This study aims to evaluate the rock overstressing that occurred in the critical cases of the TBM tunnel of the Pahang-Selangor raw water transfer project. Based on the insitu stress conditions and rock compressive strength, a possible rock failure in the form of spalling is evaluated at the tunnel sidewalls under high stresses. A numerical analysis with different approaches is adopted to simulate the extent, shape and depth of the actual failure. These approaches include the elastic analysis model, elasticperfectly- plastic model, elastic-brittle-plastic model with (residual friction r m = 0 and residual cohesion r S = 0.11) and instantaneous Cohesion-Softening Friction- Hardening (CSFH) model. A parametric study on the CSFH model strength parameters is implemented to describe the influence of the strength parameters on the extent, shape and depth of the failure, as well as to investigate which parameters could simulate the actual failure depth properly. Results are compared with the observed failure to determine which approach can predict the actual failure. Results of the CSFH model predict the actual failure depth and shape accurately since it is an elastic-brittle plastic model and can simulate the loss in the cohesion strength to low residual strength after failure. A parametric study is performed to investigate the influence of the tunnel parameters on the simulated failure zone. These parameters are tunnel lining thickness, tunnel size, tunnel overburden depth and rock scaling. Results demonstrate that the stability of the tunnel improves by decreasing the tunnel depth and removing the loose rock mass. One of the most important support elements of tunnel constructions under high overburden depth is steel fibre reinforced shotcrete (SFRS). Generally, shotcrete material shows a time-dependent behaviour after a few hours of application. Therefore, a new constitutive model of shotcrete is utilised to evaluate the time-dependent behaviour of the SFRS lining under high stresses. The SFRS lining is analysed in term of major stresses and vertical displacement using the shotcrete model and an elastic analysis method with a constant young modulus of elasticity. Considerable differences in shotcrete lining stresses are achieved when using the elastic analysis compared with that obtained by the shotcrete model. Furthermore, an attempt is made to investigate the influence of the shotcrete model input parameters on the time-dependent behaviour of the shotcrete lining. These parameters include time-dependent stiffness/strength, creep and shrinkage and steel fibre parameters. In addition, the influence of lining thickness and tunnel diameter on the time-dependent behaviour of the shotcrete lining is evaluated. The results indicate the efficiency of the shotcrete lining to resist the disturbances and transfer the loads shortly after application. The results compatible with the results of other literatures, which elucidates the efficiency of the shotcrete model to predict the steel fibre shotcrete behaviour in numerical simulation

How tunnel boundary irregularities can influence the stresses in a shotcrete lining

The shape of a tunnel boundary excavated by drill & blast in fractured rock masses is influenced by geological conditions and blasting operations. The overbreaks, apart from influencing the construction times and costs, also have an important influence on the stresses acting in the shotcrete lining, particularly when it is used as the final lining. These effects have been analyzed, on the basis of a parametric numerical analysis, and the results have shown that if the boundary shape is more irregular there are traction stresses. These tractions are not evident if a regular shape of the boundary is considered in the numerical mode

How tunnel boundary irregularities can influence the stresses in a shotcrete lining

The shape of a tunnel boundary excavated by drill & blast in fractured rock masses is influenced by geological conditions and blasting operations. The overbreaks, apart from influencing the construction times and costs, also have an important influence on the stresses acting in the shotcrete lining, particularly when it is used as the final lining. These effects have been analyzed, on the basis of a parametric numerical analysis, and the results have shown that if the boundary shape is more irregular there are traction stresses. These tractions are not evident if a regular shape of the boundary is considered in the numerical mode

Numerical modelling of ground-tunnel support interaction using bedded-beam-spring model with fuzzy parameters

The study of the ground-tunnel interaction by introducing a predetermined degree of variation (fuzziness) in some parameters of the chosen model is presented and discussed. This research comes from the consideration that tunnel model parameters and geometry are usually affected by a degree of uncertainty, mainly due to construction imprecision and the great variability of rock mass properties. The research has been developed by using the fuzzy set theory assuming that three model parameters are affected by a certain amount of uncertainty (defined by the so-called membership functions). The response of the numerical model is calculated by solving the fuzzy equations for different shapes of the membership functions. In order to investigate the effects of some model parameters, and to provide a simple procedure and tool for the designers, a study on the effect of tunnel boundary conditions, based on a fuzzy model, has been carried out using a simple but well known and widely used design method such as the bedded-beam-spring mode

Numerical modelling of ground-tunnel support interaction using bedded-beam-spring model with fuzzy parameters

The study of the ground-tunnel interaction by introducing a predetermined degree of variation (fuzziness) in some parameters of the chosen model is presented and discussed. This research comes from the consideration that tunnel model parameters and geometry are usually affected by a degree of uncertainty, mainly due to construction imprecision and the great variability of rock mass properties. The research has been developed by using the fuzzy set theory assuming that three model parameters are affected by a certain amount of uncertainty (defined by the so-called membership functions). The response of the numerical model is calculated by solving the fuzzy equations for different shapes of the membership functions. In order to investigate the effects of some model parameters, and to provide a simple procedure and tool for the designers, a study on the effect of tunnel boundary conditions, based on a fuzzy model, has been carried out using a simple but well known and widely used design method such as the bedded-beam-spring model

Numerical analysis of traditionally excavated shallow tunnels

openLo scavo di gallerie rappresenta sicuramente una tra le sfide più impegnative che un ingegnere civile possa affrontare. Ciò è dovuto principalmente alla natura tridimensionale di questo problema di interazione terreno-struttura ma anche alle numerose incertezze che possono entrare in gioco nella progettazione. Recentemente, le tecniche di calcolo numeriche, che permettono una più ampia comprensione del problema, hanno subito un notevole sviluppo, diventando una risorsa fondamentale per la progettazione di scavi in sotterraneo. Tuttavia, solo ingegneri con una buona preparazione numerica sono in grado di gestire la modellazione di problemi di interazione terreno-struttura così complessi. Inoltre, tali modelli richiedono una attenta calibrazione dei parametri e una costante validazione con dati di monitoraggio. Lo scopo di questa tesi è quello di analizzare alcune delle principali problematiche legate alla progettazione di gallerie superficiali scavate in tradizionale. Il vantaggio principale dello scavo in traditionale rispetto a quello meccanizzato è legato alla maggiore flessibilità nella scelta dei rivestimenti e delle techniche di rinforzo del cavo e del fronte della galleria. Tuttavia, una maggiore flessibilità progettuale è necessariamente legata ad una profonda conoscenza del comportamento deformativo dell’ammasso, nonché ad un utilizzo consapevole delle tecniche modellazione numerica. Il presente lavoro è principalmente incentrato sulle seguenti tematiche riguardanti la progettazione di gallerie superficiali: - la stabilità di fronti di scavo rinforzati e non rinforzati; - l’applicabilità degli Eurocodici ad una progettazione condotta mediante tecniche di modellazione numerica; - la calibrazione dei parametri del modello numerico e la sua validazione attraverso dati di monitoraggio.Among the problems that civil engineers have to face, the design and verification of an underground construction is one of the most challenging. A tunnel engineer has to tackle with a complex three-dimensional soil-structure interaction problem where many factors and uncertainties come into play. This is the reason why professional experience and engineering judgment usually play a crucial role. In recent years, numerical calculation techniques, which can provide an important basis for a better understanding of the problem, have strongly improved. They have become a fundamental resource for underground construction design, but they also entail some drawbacks: - only engineers with a strong numerical background can handle complex soil-structure interaction problems; - numerical calculations, especially if 3D, can be very time-consuming; - material parameters should be carefully evaluated, according to the particular problem and adopted constitutive law; - numerical models need to be validated with field monitoring data. The goal of this thesis is to investigate the main issues regarding the applicability of numerical analyses to the design and verification of traditionally excavated shallow tunnels. Despite, the remarkable technological improvement in mechanised tunnelling, traditional techniques still represent, in some cases, the most suitable and convenient solution. The principal advantage of traditional techniques is the high flexibility in the choice of supports and reinforcement measures. However, design flexibility implies a deep understanding of the ground response to underground openings as well as a conscious use of numerical models. This work provides a contribution to the numerical design of shallow tunnels by focusing on three principal issues: - stability of reinforced and unreinforced excavation faces; - Eurocodes applicability to a numerically-based design; - parameters calibration and numerical validation through comparison with monitoring data.INGEGNERIA CIVILE, AMBIENTALE, EDILE E ARCHITETTURAPaternesi, AlessandraPaternesi, Alessandr

Finite element modelling of transportation tunnels

The aim of this thesis is to determine the ground deformation and stress distribution around highway tunnels at various stages of excavation and for several support conditions using finite element modelling techniques. When ground is excavated and material removed the subsequent redistribution of stress in the remaining surrounding material needs to be treated by one of three methods. These are the gravity difference method, the stress reversal technique and the relaxation approach. The first two methods were chosen for the simulation of excavation in this study. The tunnel data are in the form of the dimensions of the tunnel, heights of the rock layers, details of the shotcrete lining and tunnel support systems. A pre-processing program was written to transform this information into a finite element mesh in a format suitable for use by PAFEC-FE software. This enables different tunnel models and meshes to be produced with minimum error and time. The lack of adequate post-processing facilities available in PAFEC-FE dictated that computer programs needed to be written in order to reformat the textual output files and process the mesh stress and displacement outputs for graphical display using UNIRAS. In this way repeated use could be made of PAFEC-FE without time-consuming and error-prone manual retrieval of data. The tunnels were modelled at various stages of excavation and with such support provided at those stages as to allow the computed displacements to be compared with measurements made on highway tunnels in Turkey. The stresses generated in the tunnel supports and surrounding ground were also calculated to enable the possibility of damage or failure of the support structure or ground to be assessed and the selection of an optimal support system. Insertion of a support system into the model has a marginal effect on the development of rock strength around an excavation boundary

Performance of segmental and shotcrete linings in shallow tunnels crossing a transverse strike-slip faulting

In this paper, three-dimensional numerical modeling is performed to study the effects of strike-slip fault movement on the performance of shotcrete and segmental linings in shallow tunnels that transversely cross the fault. For this purpose, a parametric study is conducted on lining thickness, soil geo-mechanical properties, tunnel depth, and fault dip angle to assess their influence on the tunnel movements and deformation. A comparison between the segmental and the shotcrete tunnels is made to highlight their performance. The results show that the greater strike-slip fault dip angle increases the separation of the lining segments. As well, after faulting, the maximum tunnel displacement in denser soils is greater than in loose soils