<title>Optical fiber sensors for monitoring strain on rebar-type and cable-type bolts</title>

Abstract

This paper describes the use of short gage length optical fiber sensors for the measurement of relative strain in rebar-type and cable-type bolts used in the mining industry to support unstable material or to keep rock masses together. For research purposes, and in order to develop numerical models for analyzing rockmass behavior, these bolts are instrumented with strain gages. For cable-type bolts, for example, traditional gages, such as foil strain gages, have proven to be inefficient or unreliable and new sensing methods have to be developed. Optical fiber-based sensors, which were surface mounted, using an epoxy resin adhesive, inside a small groove of the king wire of a 7-strand cable, could offer an attractive option for such applications. Tests include the fatigue loading of the instrumented rebar and cable bolt specimen. Stressstrain curves for both the rebar-type and cable-type bolts are provided. Practical applications and limitations of such sensor methods for bolt analysis in the future are described as welL