A new model for hollow rock bolts which comprises rock material, hollow bolt material, bolt/rock interface, is developed on the base of the composite element method (CEM). The main advantage of the new model is that it can be incorporated into the conventional finite element analysis. So the mesh generation of bolted rock structures becomes more convenient and feasible, which is very important in the optimisation of reinforcement design: the mesh can be kept unchanged when the number and orientation of bolts are adjusted. The comparison of the calculation results with a conventional FE approach shows the robustness of the proposed method.

Un nouveau modèle numerique de boulons creux comprenant la roche, le materiau du boulon creux et l'interface roche / boulon est developpe sur la base de la methode des elements composites (CEM). L'avantage principal du nouveau modèle est la possibilite de l'incorporer dans une analyse aux elements finis conventionnelle. Ainsi la generation du maillage d'une structure rocheuse ancree devient plus simple ce qui est très important pour une optimisation du projet: en cas d'ajustement du nombre et de l'orientation des boulons, le maillage reste inchange. La comparaison de resultats de calcul avec ceux obtenus par un code aux elements finis conventionnel montre la robustesse de la methode proposee.

Auf der Grundlage der Verbund-Element-Methode (CEM) wird ein neues Modell fuer hohle Reibungsanker entwickelt, das den Fels, das Ankermaterial und die Kontaktflache Fels / Anker umfasst. Der Hauptvorteil des neuen Modells ist die Möglichkeit, es in eine konventionelle FE-Analyse einzubetten. So wird die Netz-Generierung fuer verankerte Fels-Bauwerke einfacher, was fuer die Optimierung des Verankerungs-Projekts von Wichtigkeit ist: wenn Zahl und Orientierung der Anker variiert werden, bleibt das Netz unverandert. Der Vergleich von Rechenergebnissen mit solchen aus einer konventionellen FE-Rechnung zeigen die Robustheit der vorgestellten Methode.

Introduction

The ‘Swellex’ bolt is a hollow metallic bolt which is completely connected to the rock mass. In the FE analysis of such supported rock structures, it is essential to formulate a bolt element which can simulate the radial expansion and compression effects besides the common shear tension effects along the axis. An explicit bolt element model will have higher potential to meet the above request.

There are several explicit bolt element models proposed by Aydan1, Swoboda & Marence2, Chen & Egger3, etc. All of these explicit bolt element models have the same characteristics: they are conventional elements which have definite nodes, and some of these nodes should be the common nodes with the nearby rock material elements. Consequently, the existence of a large quantity of bolts will impose very strong restraints on the finite element mesh generation. Based on the composite element method (CEM), explicit element models have been proposed for both the fully grouted bolt and the hollow friction bolt4,5.

This paper will present the theory and implementation of the new element model of hollow bolts firstly, then the conventional FEM and CEM are both applied for a numerical example.

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