ABSTRACT:

Considering the rational design of tunnel support using the New Austrian Tunneling Method, a theoretical model which considers a proper interaction mechanism between the ground and the grouted rock bolts is put forward in the paper. According the strain-softening behavior of rocks and bolt pattern, nine cases of the ground-bolts interaction modes are presented to describe the mechanical stabilization of a reinforced rock mass near a tunnel. By a detailed parametric study, an approach for the estimation of the rational bolting is provided by the evaluation of effect of controlling the extent of the plastic zone and tunnel convergence. The verification of the proposed theory is made by the base friction model test.

RESUME:

Dans Ie cadre d'une conception rationelle du soutien des ouvrages à l'aide de la Nouvelle Methode Autrichienne de Percement des Tunnels, un modele theorique utilisant un mecanisme interactif adapte entre Ie sol et les piliers rocheux betonnes est mis en avant dans cet article. Compte tenu de la faculte qu'ont les roches pour reduire les contraintes, et du principe des piliers, neuf cas d'interactions sol-piliers sont presentes pour decrire la stabilisation mecanique d'une masse rocheuse renforcee a proximite d'un tunnel. Grace a une etude parametrique detaillee, une approche de I'estimation du rôle des piliers est fournie en evaluant les effets du contrôle du niveau de la zone plastique et de la convergence du tunnel. La verification de cette theorie est realizee a l'aide des tests de modelisation des frictions de base recemment mis au point.

ZUSAMMENFASSUNG:

Unter Betrachtung des rationalen Entwurfs von Tunnelunterstuetzung mit Verwendung der Neuen Östereichischen Tunnelbaumethode wird in dieser Abhandlung ein theoretisches Modell vorgestellt, das einen angemessenen Wechselwirkungsmechanismus zwischen dem Erdboden und den vermörtelten Felsbolzen betrachtet. Entsprechend dem SpannungserWeichungsverhalten von Fels und Bolzenmuster werden neun Falle von Wechselwirkungsarten zwischen Erdboden und Bolzen prasentiert, um die mechanische Stabilisierung einer verstarkten Felsmasse in der Nahe eines Tunnels zu beschreiben. Durch eingehende parametrische Untersuchung wird durch Auswertung der Wirkung der Kontrolle des Ausmaßes der plastischen Zone und der Tunnelkonvergenz eine Annaherung fuer die Schatzung der rationalen Bolzenanbringung geboten. Die Bestatigung der vorgeschlagenen Theorie erfolgt durch die neu entwickelte Basisreibung-Modellpruefung.

1 INTRODUCTION

Grouted rockbolts are nowadays frequently applied in tunnels and underground openings, even in weak ground conditions, for improving the stability and for maintaining the load-bearing capacity of the rock mass. Since the reinforcing effect of rockbolts largely depends on the grout strength and deformational behaviors of both the rockbolts and the rock mass, a proper clarification of the interaction mechanism between the ground and the rockbolts is of basic necessity for the optimum design of bolting pattern. A number of fundamental analysis with respect to the supporting and stabilizing influence of rock reinforcement have been presented since the early 1940s(Reed et al. 1993), in which the function of rockbolts is often considered to be an equivalent uniform internal pressure acting on the tunnel wall (Rabcewicz & Golser 1973, Hoek & Brown 1980, Labiouse 1991, etc.). Recently, there are some new analytical proposals to illustrate the rockbolt-ground interaction in association with the deformation of the ground. For example, Indraratna & Kaiser(l990a, 1990b) introduced an analytical approach for assessing the influence of fully grouted rockbolts. They assumed that the mechanical effect of fully grouted rockbolts is due to the shear stress on the rockbolt- ground interface caused by the relative displacement between the rockbolts and the ground, and extended an elasto-plastic solution for their proposed model. This approach has made a progress in considering the influence of the grouted rockbolt ground interaction on the tunnel behavior. However, how the influenced effect of the rockbolt-ground interaction varies with the characters of material, especially the post-failure behavior, and how to carry out the optimum design of bolt pattern according to the ground condition have not been quantitatively illustrated yet in the above mentioned proposals.

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