ABSTRACT:

When the amount of field measurement data is not enough to know the whole behavior of rocks around a tunnel, the computer analysis can be used to complement those informations. This paper presents an example which introduces the calculation method of the relaxed zone in rocks by BEM analysis using the data from field measurements. Taking into account the in-situ condition of rocks in BEM analysis, "an empirical failure criterion for rock" was used as follows; 61/6c = 63/6c+ mr. 63/6c + sr, where mr and sr are constants which depend upon the in-situ properties of rocks. After determination of relaxed zone by measurement on certain locations, it is shown that the calculated relaxed zone by proper value of those constants coincides with the above result. Accordingly, the complete relaxed area of rocks around a tunnel can be determined.

RESUME:

Lorsque le nombre de mesures sur le terrain n'est pas suffisant pour connaître, le comportement entier des roches autour d'une galerie, l'analyse par ordinateur peut être employee afin de completer ces informations. Cet article presente un exemple qui introduit une methode de calcul sur la zone detendue dans les roches par l'analyse des elements frontiers(BEM) en utilisant les donnees saisies sur le terrain. compte tenu de l'etat des roches in-situ, en analyse des elements frontiers, "un critère empirique de rupture pour la roche" est utilise comme suit; 61/6c = 63/6c + mr. 636c+ sr, où mr et sr sont les constantes qui dependent des proprietes in-situ de roches. Après la determination de la zone detendue par la mesure sur quelques endroits, il est demontre que la zone detendue calculee par les valeurs convenables de ces constantes colncide avec le resultat ci-dessus. Par consequent, la zone detendue entière autour d'une galerie peut être determinee.

ZUSAMMENFASSUNG:

Wenn die Messergebnisse fuer die Erklarung des Verhaltens der Gesteinsstrecke nicht vollstandig sind, könnte die Bestimmung durch EDV die fehlende Information ergazen. Im folgenden wird ein Beispiel dargestellt, wie das Rechenverfahren mit Feldmessungsdaten durch BEM Analyse die Relaxation des Gebirges auswertet. Beruecksichtigt man die in-situ Bedingung des Gebirges im BEM Analyse, wird das folgende empirische Bruchkriterium benutzt, 61/6c= 63/6c + mr 63/6c+ sr, wo mr und sr die von der in-situ Eigenschaften des Gesteins abhangigen Konstante sind. Die Relaxation des Gebirges stimmt mit dem durch Einsatz von den ausgeglichenen Konstanten berechneten Resultat gut ueberein, das durch Messergebnisse punktweise cfestzustellen ist, somit der ganze Relaxationsumfang auswerten last.

INTRODUCTION

The main purpose of field measurements in rock mechannics is to know the behaviors of rocks around openings. Of various measuring techniques developed, monitoring the displacements has proven to be a simple and useful method to estimate the stability of a tunnel and the relaxed boundary in rocks. Especially the latter becomes an important parameter for designing the support systems.

After estimation of relaxed zone on certain locations around a tunnel by measurements, it is required to know the whole relaxed state in rocks, which can be established by computer analysis like the finite element method or the boundary element method.

This paper presents an example introducing the combining techniques of field measurements with computer analysis in calculation of the relaxed zone in rocks.

As a result, it is shown that even a small amount of data from measurements can offer useful informations to the computer analysis which is the next step of interpretations.

MEASUREMENT OF DISPLACEMENTS AND CONVERGENCES
Instrumentation

and convergences of a tunnel, the single rod extensometers and the tape extensometer as shown in figure 1, were used; those are commercially available instruments. Figure 2 shows the installation of single rod extensometers of which lengthes are 1 or 2 meters. By attching a hook on the cap of a rod, head of the rod became the measuring point for the tape extensometer.

(Figure in full paper)

Results and interpretations

The relative displacements between two fixed points an end point is fixed in depth of rocks and a measuring point is fixed on the tunnel section, were measured for 68 days by rod extensometers. The results are shown in figure 3.

Considering those results, assumptions are possible as follows;

  1. In view of the fact that the increasing rate of displacements of the rod A1 slowed down ahead of that of the rod A2, we can suppose two possible cases. Firstly, the end point of the rod A1 exists in the relaxed zone, but the end point of the rod A2 still remains in the elastic region of rocks. Secondly, both of the end points of the rod A1 and A2 are

(Figure in full paper)

relaxed zone, but the end point of the rod A2 still remains in the elastic region of rocks. Secondly, both of the end points of the rod A1 and A2 are sequentially embedded in relaxed zone.

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