ABSTRACT:

Rockbolts/rock anchors are one of primary reinforcement/support members and utilized widely in both civil engineering and mining engineering. They are generally fixed into rock mass through boreholes utilizing cement or resin-based bonding material. Therefore, their bonding strength under both static and dynamic loading conditions are of great importance. The authors developed a new testing device to investigate the behaviour of rocks subjected to different testing conditions under shock loads. In this study, tendons fixed by rapid-hardening cement-based grouting material into 30 mm boreholes in 90-100 mm high cylindrical marble and Ryukyu limestone blocks are subjected to shock loads and their bonding strength characteristics are evaluated. The same type samples are also tested under static conditions and they are compared with those obtained from impact loading tests. The authors report the outcomes of these experiments and discuss their implications in practice.

1. Introduction

Rock dynamics is now one of the most important topics in the field of rock mechanics and rock engineering. The load bearing capacity of the rockbolts and rock anchors are governed by the shear behavior of interfaces such as grout-bar (cable) and grout-rock interfaces. Their mechanical behavior under conventional direct shear, shear creep and cyclic loading conditions were studied experimentally by Aydan (Aydan, 1989; Aydan et al. 1994). These tests were mainly based on the static direct shear tests and one-way cycling shearing load pattern with the consideration of wind loads on pylons.

The dynamic loads on rockbolts and rock anchors occur when rock engineering structures are subjected to earthquakes, rockburst or blasting loads. Fig. 1 shows an example of rupturing of cable-type rock anchors used for reinforcing a rock slope due to the 2008 Iwate-Miyagi earthquake. Fig. 2 shows the state of rock anchors and rockbolts at underground excavations experienced rockburst and spalling problems.

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