ABSTRACT:
Non-destructive rock bolt testing in the field remains to be a challenge. This paper reviews a research project in developing such a field testing technique and presents important findings up to date. The research, using guided waves, has been focused on understanding of the fundamental wave characteristics in grouted rock bolts. Extensive laboratory experiments and numerical simulations were conducted. During experiments, guided waves with specific input frequencies were used to study the characteristics of the rock bolts embedded in concrete. Numerical simulation using finite element method, which produced signals matching well those from experiments, was used to determine the wave attenuation coefficient, energy loss and boundary effects. These results are very valuable for field rock bolt testing.
1 INTRODUCTION
Rock bolts have become the major rock mass supporting system in rock engineering. Majority of these bolts are installed by grouting. Field testing and monitoring of the installed rock bolts is essential to evaluate their effectiveness and performance. The conventional methods of pull-out test and torque wrench test are time consuming and often destructive as well (Choquet 1991, Kelly & Jager 1996, Zou 2004). Non-destructive testing would therefore be a preferred choice. However, there has not been such an instrument available for field use, which can determine quickly and reliably the effective bolt length, bolt integrity, bolt tension, bolt holding capacity and grout quality. Over the last two decades, research on nondestructive rock bolt testing has been very active and some progress has been made (Thurner 1988, Tadolini 1990, Rose 1999, Vrkljan et al. 1999, Beard et al. 2003, Madenga et al. 2006, Zhang et al. 2006, Cui & Zou 2006, Zou et al. 2006). Prototypes of devices have been developed to measure the bold tension in the non-grouted section of a bolt and the grout quality in a non-quantitative format.
