SUMMARY:

A major factor hindering the detailed application of the method of characteristic lines in underground excavation design is the difficulty of determining realistic rock mass properties and allowing for them in the calculations. A new method of making rock-support interaction calculations for plane strain, axi-symmetric pressure shaft and tunnel problems is presented. This method uses non-linear peak and residual rock mass strength criteria, allows for strain-softening and the development of plastic volumetric strains, calculates the distribution of groundwater pressures by allowing the permeability of the fractured rock mass in the plastic zone to vary with the square of the volumetric strain, and evaluates the influence of water pressure subsequently applied inside the lined excavation.

ZUSAMMENFASSUNG:

Ein Hauptfaktor der die ausfuerliche Anwendung der Methode der charakteristischen Linien im Untertage Ausgrabung Entwurf verhindert, ist die Schwierigkeit die reele Felsmasse Elgenschaften zu bestimmen und in die Berechnung zu beruecksichtigen. Eine neue Methode die die Fels-Unterstutzung Aufeinanderwirkung fuer ebenen Zwang axialsymmetrische Druckschachte-und Trunnelprobleme berechnet ist dargestellt. Diese Methode wendet nicht- lineare Bruch-und Restfestigkeit Felsmasse Kriteria an, beruecksichtigt den Festigkeits a b fall und die Entwicklung von plastischen Volumetrischen Formanderungen, berechnet die Verteilung des Grundwasserdrucks bei ermöglichen die Durchlassigkeit der gebrochenen Felsenmasse in die plastische Zone mit dem Quadrat der Volumetrischen Formanderung zu verandern und den Einfluss des nachtraglich an der Innenseite der verschalenen Ausgrabung aufgelegenen Wasserdrucks abzuschatzen.

RESUME:

La utilisation de toutes les possibilitees de la methode des characteristiques est empechee par des difficultes au niveau pratique presentees par la determination de la loi de comportement global du massif fissure, et par des difficultes au niveau mathematique de tenir compte de ce comportement lors du calcul, On presente ici une nouvelle methode d''analyse de l''interactillnentre une structure de soutenement et le massif, pour le cas de contraintes planes tel qu''un tunnel, et pour le cas axisymmetrique d''un puit. Cette methode permet l''utilisation des criteres non-lineaires de resistance maximale et residuelle, et elle permet de tenir en compte les phenomenes de l''anti-ecrouissage et de l' evolution de la dilatation plastique. La variation de la pression d''eau souterraine se calcule a partir de l''hypothese qu''a l''interieur de la zone plastique, le permeabilite des roches fissurees est proportionelle à la deformation volumetrique au carre, et on tlent compte lors du calcul de l''influence de la pression interne sur Ie paroi de la cavite souterraine.

INTRODUCTION

The development of stresses and displacements in the rock surrounding tunnels and shafts and in the lining or support elements has long been studied using ground support interaction analyses. The use of what is known as the method of characteristic lines or the convergence-confinement method produces ground-support interaction diagrams which show the inter-relationships between the rock mass properties, the in-situ stresses, the type and stiffness of the lining or support and the timing of its installation. The general principles elucidated by this approach are now widely understood and applied in practice, particularly in conjunction with field measurements as in the New Austrian Tunnelling Method (Rabcewicz, 1964).

Despite these advances in general under st.anoi.ng, the basic concept s of ground-support interaction have not, as yet, been incorporated into a widely applied method of making pre-excavation design calculations. This can be attributed, in the main, to two major factors:

  • the difficulty of adequately predetermining the range of rock mass properties required for use in such calculations; and

  • The analytical and computational difficulties associated with solving other than axi-symmetric problems taking into account realistic rock mass properties which generally involve non-linearities and strain-softening post-peak behaviour.

This paper considers the models of rock mass behaviour that have been previously used in rock-support interaction calculations, and proposes a new model of the relevant rock mass properties. The application of this model is illustrated through the solution of an axi-symmetric pressure shaft problem in which the distribution of water pressures throughout the problem domain is taken into account.

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