This paper describes the results of a fundamental test of a cement grouted permanent rock anchor with a working load of 2780 kN (load at the yield limit: 4900 kN). The attempt was made to approximate the rock mass conditions around the bond length with a plane analytical calculation and to allocate them to a concreted steel tube. The axial and tangential strains of the steel tube were gauged to determine the course of the load transmission. The large-scale test was simulated by the Finite Element Method. The results show a good conformity with the theoretical basis explained in the beginning of this publication. The assigned measures against corrosion proved to be sufficient.
Cette communication donne les resultats d'un essai portant sur un tirant d'ancrage sous charge normale de 2780 kN (charge limite 4900 kN). On a essaye de reproduire les conditions presentes dans la masse rocheuse de la zone de liaison à l'aide d'un modèle de calcul plan, et ensuite de les mettre en rapport avec l'evolution d'un tuyau d'acier dans du beton. On a mesure l'effort axial et tangentiel du tuyau d'acier afin de determiner la repartition de la charge. Cet essai à grande echelle a ete simule par la methode des elements finis. Les resultats obtenus concordent bien avec la theorie exposee dans l'introduction. Les dispositions prises pour empêcher la corrosion se sont averees suffisantes.
In diesem Beitrage werden die Resultate der Grundsatzpruefung eines zementmörtelverpreβten Felsankers mit einer Gebrauchslast yon 2780 kN (Grenzlast 4900 kN) vorgestellt. Dabei wurde der Versuch unternommen, die Gebirgsverhaltnisse im Haftstreckenbereich unter Hinzuziehung eines ebenen analytischen Verfahrens in einem betonierten Stahlrohr nachzubilden. Zur Ermittlung des Verlaufs der Krafteinleitung wurden die axialen und tangentialen Dehnungen des Stahlrohres gemessen. Der Groβversuch wurde mit der Methode der Finiten Elemente simuliert. Die Ergebnisse zeigen gute Übereinstimmung, auch mit den zu Beginn der Arbeit dargelegten theoretischen Grundlagen. Die fuer Anker der untersuchten Bauart vorgesehenen Korrosionsschutzmaβnahmen erweisen sich auch fuer einen Anker dieser Tragfahigkeit als ausreichend.
Today the cement grouted permanent rock anchor is taken to be a nearly perfect and economic construction suited for the use in rock mechanics overground as well as underground. Relative to its capacity no constructive limits seem to exist. Thus rock anchors with an ultimate load capacity of more than 12,5 MN were applied to increase the height of dams. In the Federal Republic of Germany soil and rock anchors must be licensed. For every type of design fundamental tests are prescribed to guarantee high safety standards. The load transmission within the bond length and the constructive measures against corrosion are of special interest in this connection, because these properties depend on the construction.
Generally anchors are distinguished in so-called Druckrohr anchors (type A), bar anchors (type B) and strand anchors (type C). An anchor of type A transmits the prestressing at its base subjecting the bond length to compression and shear. Anchors of types Band C have their load maximum at the top of the bond length, which is strained by tension and shear. Bar and strand anchors are objects of the following report. The prestressing working in the anchor tendon is transmitted to the cement and the surrounding rock mass by bond. The bond stress distribution between grout and tendon can be determined as the first differential quotient of the steel tensile stress distribution. Jirovec (1979) verified this relationship in extensive test series on self-developed measuring anchors and on commercial bar anchors which were prepared with strain gauges. The maximum value of the shear stresses divides the bond length into an adhesion zone and a friction zone, wherein the bond is interrupted by slip (Fig. 1a). According to the increase of force the peak of the bond stress is shifted more and more from the proximal end to the rock side end of the anchor caused by progressive slip. Within the friction zone the cement is ruptured into discs. Nevertheless the anchor can be taken as fully resistant in this zone due to dilatation and wedging of the mortar. Fig. 1b shows the results of a pull-out test on a ribbed anchor tendon of 26,5 mm diameter which verify the relations mentioned above. It is not possible to get higher shear stresses, the peak becomes flatter and the rear part of the bond length is subjected to strain. The studies made by Jirovec (1979) have shown that prestressing forces up to 500 kN are able to be decreased on less than one meter of bond length as a function of surface conditions and diametre of the tendon. This tendency could be observed on rock anchors with working loads up to 1800 kN in diverse suitability tests.
