ABSTRACT
This paper presents a method of computation which for economic comparison produces a system of pattern rock reinforcement that is structurally equivalent to an internal tunnel support system. If it is assumed that the internal support system is acted upon primarily by thrust, then to be structurally equivalent to an internal support system, the rock reinforcement system must be able to carry an equal amount of thrust. The thrust capacity of a zone of reinforced rock is a function of its effective thickness, and the increase in rock mass strength which results from the confining pressure provided by the rock reinforcement. By making basic assumptions about the properties of the rock mass, one can compute a reinforcement pattern which will provide sufficient confinement to the rock mass to increase its load carrying capacity by an increment which is equivalent to that provided by the internal support.
Au but d'une comparaison économique du dessein des tunnels, ce rapport présente une méthode d'estimation d"une système régulière du renforcement rocheux qui est l'équivalent morphologique d'une système des appuis internes. Supposons q'une système des appuis internes soutient surtout la pression, il se trouve que pour être l'équivalent morphologique, la système de renforcement rocheux doit être capable de soutenir une pression équivalent. La portance d'une zone de roche renforcée est une fonction de la épaisseur effective et aussi de la résistance accroissements que provient de la pression de soutien fourni par le renforcement rocheux. En faisant des suppositions à propos des attributs physiques du milieu rocheux, on peut estimer une système régulière de renforcement, qui donne a la roche une pression assez élevé de faire augmenter sa capacité portante jusqu'elle devient l'équivalent des appuis internes.
Dieser Bericht stellt eine Berechnungsmethode dar, die für ökonomische Vergleichung ein Gesteinsverstärkungs-System vorbringt das genau so kräftig ist wie ein innerliches Tunnelunterstutzungs-System. Wenn es voraussetzt ist, dass beide Unterstützungs-Systeme sich wie Bögen betragen, und dass jeder Bogen eine specifische Tragfähigkeit hat, dann sind beide Systeme äquivalent wann die Tragfähigkeit des verankerten Felsbogens gleich ist mit der Tragfähigkeit des innerliches Unterstützungs-System. Die Tragfähigkeit des verankerten Felsbogens ist abhängig an seine brauchbare Dicke und die Druckfestigkeitserhöhung der Felsmasse. Die Druckfestigkeitserhöhung der Felsmasse folgt aus dem Felsankerseitendruck. Mann kann mit grundlicher Annehmungen von dem Eigenschaften der Felsmasse eine Felsankersystem berechnen, der genugsam Seitendruck gibt dass die Tragfähigkeit der Felsmasse zu einem innerliches Unterstützungs-System äquivalent ist.
Internal support structures consisting support structures have been designed using of timber or timber and steel are the types steel sets in conjunction with wood lagging of rock support which have most commonly and occasional rock bolting for rock block been used in the design of tunnel excavations, stabilization. During the last two decades, Most of the more recent internal rock reinforcement has also become an accepted alternative means of primary rock support, especially in large tunnels and large underground chambers. Rock reinforcement has many proven advantages over internal support structures as a method of stabilizing the rock around a tunnel opening. Firstly, rock reinforcement provides a more immediate resistance to rock movement than do steel sets or timber supports . With rock reinforcement the rock surrounding the opening is tied together and converted to a self-supporting structural unit. Consequently, the rock mass does not undergo as much deformation prior to stabilization as it does when supported by internal supports. Secondly, rock reinforcement is far more adaptable to the sequence of excavation and other construction operations. In tunnels requiring multiple heading excavation, reinforcement can be in- stalled at the face of each excavated heading. This is not possible with an internal support structure such as that consisting of steel set supports, since set installation is delayed until the full arch is excavated. For this reason, rock reinforcement is more effective than an internal support structure since it prevents excessive loosening of rock blocks as the opening is enlarged, and results in a reduced loading on any final lining. Rock reinforcement is less susceptible to damage from blasting than internal supports and can be placed closer to the working face. In addition, it interferes less with drilling operations and allows greater control of excavation tolerances resulting in less overbreak and smoother tunnel walls. The decision to use rock reinforcement as the method of primary tunnel support will, in most cases, be based on economics. The cost of internal support compared to reinforcement in terms of the total project costs will have a major influence on which method is ultimately employed.
