Field measurements are well recognized as powerful tool for monitoring the stability of rock structures such as tunnels, underground caverns, slopes, etc. The measurement results must be properly interpreted without delay in assessing the adequacy of the original design and construction method. In the interpretation of the results, back analysis plays a important role. In this paper, the role of back analysis is described in association with engineering practice. It is emphasized that back analysis is not simply backward calculation, but its basic concept should be different from the one of ordinary analysis. A method of back analysis is proposed for interpreting the non-elastic behaviour of rocks. A case study demonstrates that it is well applicable to engineering practices.


On reconnaît generalement que les mesures in situ sont un outil puissant qui permet de controler la stabilite des ouvrages construits dans les massifs rocheux, tels que les tunnels, les grandes excavations souterraines, les talus, etc. Les resultats des mesures doivent être interpretes sans delai pour s'assurer de la conformite du projet initial et de la methode de construction. Dans l'interpretation des resultats, l'analyse a posteriori joue un rôle important. Dans la presente communication ce rôle est decrit eu egard aux applications pratiques. On insiste sur le fait que l'analyse a posteriori ne constitue pas seulement un calcul en retour mais doit être conçue differemment d'un calcul ordinaire. On propose une mêthode de calcul a posteriori permenttant d'interpreter le comportement non elastique des roches. Une etude de cas montre qu'elle s'applique bien en pratique.


Feldmessungen sind anerkannt als wichtiges Hilfsmittel zur Kontrolle der Stabilitat von Bauwerken im Fels wie Tunnels, Kavernen, Böschungen usw. Die erhaltenen Messresultate muessen umgehend ausgewertet werden zur Beurteilung der Adequatheit des urspruenglichen Entwurfs und der Baumethode. Bei der Interpretation der Resultate spielt die "Rueckrechung" eine wichtige Rolle. In der vorliegenden Arbeit wird diese Rolle im Umfeld der Ingenieurpraxis beleuchtet. Es wird unterstrichen, dass unter "Rckrechung" nicht einfach eine rueckwarts durchgefuhrte Berechnung verstanden wird, sondem dass ihre Grundlage auf einem anderen Konzept beruht als diejenige einer "normale" Berechnung. In diesem Licht wird eine Methode der Rueckrechnung zur Interpretierung des nicht elastischen Verhaltens von Fels vorgestellt Ein Anwendungsbeispiel beweist die Aussagekraft dieser Methode.

1. Introduction:

Various computational methods such as the finite element method, boundary clement method, discrete element method etc., have rapidly developed in the field of geomechanics during the last decade. Some of them have already been extensively used in engineering practices for the prediction of mechanical behaviour of structures such as tunnels, large caverns, slopes, foundations, and so on. It is well recognized, however, that the real behaviour of the structures often differs from the one predicted by the computational methods, although sophisticated computational techniques are used. This difference may be mainly due to the fact that many uncertain factors are involved in computational analysis, that is, the geological and geomechanical characteristics of rocks and/or soils, underground water table, initial state of stress, etc. are so complex that they cannot be easily evaluated prior to the design work. In order to overcome difficulties in predicting the behaviour of structures, field measurements are conducted during their construction. The geological and geomechanical parameters used in design analysis are re-evaluated by considering the results of field measurements, and, if necessary, the original design and the construction procedure can be modified to achieve the rational design of structures. This design and construction method was named the observational procedure by Terzaghi and Peck (1948). In this method, the most important thing is how to interpret the field measurement results.

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