The mechanical behaviors of fully-grouted long-embedded cablebolts actually used in situ are very non-linear in pull tests and are different from those of short-embedded cablebolts. We have conducted the pull tests of long-embedded cablebolts installed in mockup rock test blocks, which are 4m in the longitudinal length. In order to investigate the mechanical behaviors inside the test block, the axial load distribution along the cablebolt and locations of acoustic emission events were measured during each pull test. It was found that the axial force distributions were quite linear and that the gradients were interpreted as the grout bond strength by taking into consideration the stress balance at the infinitesimal segment of a cablebolt.

Les boulons-cables longs entièrement cimentes qui sont reellement utilises sur place presentent, au cours des essais de traction, des comportements mecaniques considerablement non lineaires et differents de ceux des boulons-cables courts. Nous avons mene des essais de traction des boulons-cables longs installes dans une maquette de fond rocheux servant d'eprouvette d'une longueur longitudinale de 4 m. Afin d'etudier les comportements mecaniques interieurs de l'eprouvette, la repartition de la force axiale du boulon-cable et l'emission acoustique ont ete mesurees durant chaque essai de traction. Il s'est avere que les repartitions de la force axiale sont sensiblement lineaires et que leurs gradients representent la resistance d'adhesion en prenant en compte l'equilibre de contraintes à la partie infinitesimale d'un boulon-cable.

Das mechanische Verhalten von ganz eingegossenen, lang eingebetteten Kabelbolzen, die vor Ort eingesetzt werden, ist bei Zugpruefungen sehr nichtlinear und anders als das von kurz eingebetteten Kabelbolzen. Es wurden Zugpruefungen mit lang eingebetteten Kabelbolzen durchgefuehrt, die in Pruefblöcken (Gesteinsattrappen) mit 4 m Lange eingelassen waren. Zur Untersuchung des mechanischen Verhaltens in den Pruefblöcken wurden die Axiallastverteilung entlang des Kabelbolzens sowie das Auftreten von Schallemission im Verlauf jeder Zugpruefung gemessen. Es ergab sich, dass die axiale Kraftverteilung recht linear ist, und die Gradienten wurden unter Beruecksichtigung des Kraftegleichgewichts am infinitesimal kleinen Punkt eines Kabelbolzens als Haftfestigkeit interpretiert.

Introduction

Cablebolts, composed of multi-wire strand, are capable of being installed as long reinforcement bolts from small adits due to their flexibility. As a rational rock-reinforcement method, cablebolting has been used in construction projects of large cross-sectional three-lane road tunnels1) and a large underground powerhouse cavern2) in Japan.

The authors have carried out laboratory pull tests of cablebolts to investigate the mechanical behaviors of cablebolts in the scope of establishing the quantitative evaluation of the effects of rock reinforcement by means of cablebolting.3) 4) In these studies, cablebolts of short embedded length of 350mm were used in their pull test and differences in grout bond strength etc. for types of cablebolts were discussed. However, it has been reported that cablebolts of long embedded length actually used in situ show significant non-linearity in the load-displacement relations of the pull tests1) whereas those of short-embedded length show fairly linear behavior before reaching the peak bond strength.3) 4)

In this study, we have conducted the pull tests of long-embedded cablebolts installed in large-scale mockup rock test blocks, which are 4m in the longitudinal length. The axial load distributions are measured together with the load-displacement relations during the pull tests.

This content is only available via PDF.
You can access this article if you purchase or spend a download.