Η εργασία έχει πραγματοποιηθεί στην περιοχή της ΤΡΑΠΕΖΑ (ΔΙΑΚΟΦΤΟ). Κατά την διάρκεια της διαδικασίας είχαμε την ευκαιρία να μελετήσουμε όλες τις μεθόδους εκσκαφής της γαλαρίας και να παρθούν ορισμένα δείγματα για περαιτέρω εξέταση στο εργαστήριο. Έτσι σε γενικές γραμμές μπορούμε να πούμε ότι: Οι σχηματισμοί που συναντούμε είναι κυρίως από χαλικοπαγή - κροκαλοπαγή με στρώσεις μάργας και το αντίθετο. Δεν υπάρχει σημαντική παρουσία υπόγειων υδάτων, κυρίως συναντούμε μικρούς θύλακες νερού κατά την διάρκεια της εκσκαφής. Η μέθοδος που ακολουθήσαμε είναι η ΝΑΤΜ και σύμφωνα με αυτή έχουμε καταγράψει όλα τα αναγκαία μέτρα που έχουν ληφθεί. Επίσης πρέπει να αναφερθεί η γεωμηχανική ενοργάνωση που έχει εγκατασταθεί στην γαλαρία. Κλείνοντας όσον αναφορά τις εργαστηριακές δοκιμές που έχουν ολοκληρωθεί έχουμε καταλήξει στα κύρια φυσικά και μηχανικά χαρακτηριστικά της μάργας. Τα σχετικά αποτελέσματα των δοκιμών παρουσιάζονται αναλυτικά στην εργασία. / This project has taken place in the area of TRAPEZA (Diakofto). During the process we had the opportunity to study all the excavation methods of the tunnel and to take some samples for further study in our lab. So in general lines we can say that: The formations that we encounter are mainly of gravel conglomerates with layers of marls and the opposite. There is not significant presence of underground water, mainly we introduce small pockets of water during the excavation process. The method that we followed is the NATM and according with this method we have recorded all the necessary measures that have been taken place. Also must be mentioned the geomechanical instrumentation that has been installed into the tunnel. In conclusion as far the lab tests we have conclude to the main physical and mechanical characteristics of the marl. A Thorough documentation of the obtained results is included in the project.

In tunnel excavation, the use of rockbolts has long been a popular means of reinforcement in rock masses to prevent the rock opening from caving in. The idea has evolved from the earliest form of rockbolt made of wood to the more up-to-date form of pre-tensioned or grouted steel rockbolts. A major breakthrough in the design of rockbolt models was made by Aydan (1989). This rockbolt element was modelled in coupled form, with one sub-element representing the steel bolt, and the other sub-element the grout. This representation was necessary to model the complex action in the continuous rock mass near the joint. In elasticity problems, the large displacement formulation of a beam element is derived from the fundamental theory, and the bending phenomenon of a thin rod is analysed by the finite element discretizations of the bar elements and the beam elements. Experiments show that the deformation characteristics of the latter representation resemble a more realistic life behaviour. Based on this finding, this thesis proposes a modification to Aydan's two-dimensional rockbolt element, with the beam elements discretising the steel bolt. The different mechanical responses of a perfectly elastic rockbolt are considered, and the large displacement formulation of the new rockbolt element is derived by combining those of Aydan's rockbolt element and the beam element. The mechanics of the Aydan element and the new rockbolt element are described, and their performances are compared in an identical situation. It is found that in the two two-dimensional examples used in this thesis, the modified element ensures the continuity of curvature of the rockbolt, and in general, can act as support across a discontinuity or joint between rock masses well. In conjunction with the displacement method in the finite element procedures, a conventional iteration solution procedure is first described to solve the nonlinear incremental stiffness equation. However, it is found that this procedure is cumbersome, and requires a large amount of comptutations. Some limited storage quasi-Newton minimization algorithms are considered as an alternative.

In this study, excavation of jet-grouted tunnels in ground with strong time-dependent behavior is analyzed. The constant growth of population has led to a constant increase in the price of lands and thus infrastructures. Underground alternatives are becoming more economical. Furthermore, advances in the construction technology have made it feasible to construct tunnels in difficult ground conditions. By providing a grouted arch ahead of the tunnel face, jet-grouting has proved effective for the stability and performance of tunnels in difficult conditions. Given the limited depth of jet-grouting into the face, the jet-grouted arch is loaded soon after installation, when the rigidity of the grouted material is growing significantly. The simultaneous loading and hardening of the jet-grouting makes the tunnel response depend on the excavation rate. Furthermore, in difficult tunneling conditions, the ground material is associated with highly viscous behavior. This behavior is synonymous with delayed deformation depending on the level and duration of the ground loading by the tunnel excavation. In order to show the importance of the time-dependent behaviors, the full-face and the sequential excavation method are compared using three-dimensional and two-dimensional finite element analyses. First, a three-dimensional model is constructed and its results are validated against available analytical solutions for time-independent behaviors. The hardening of the jet-grouting is then introduced into the model by embedding jet-grouting elements through the analysis. In order to account for the ground viscous behavior, an advanced viscoplastic constitutive model is adopted, numerically implemented in FORTRAN, and used in conjunction with finite element software ABAQUS. The excavation methods are compared for the well documented study case of Tartaiguille tunnel. The results indicate that the full-face method outperforms the sequential method in the studied case by installing the tunnel invert closer to the face. The two-dimensional analysis of the tunnel is conducted by using the convergence-confinement method. To this end, a new approach is introduced to use the method for tunnels in time-dependent conditions. The effect of the jet-grouting hardening and the ground viscous behavior is characterized within the new approach by deriving the ground convergence curves. The reverse dependency of these mechanisms on the tunnel advance rate leads to an optimum advance rate, at which minimum tunnel convergence develops. / text