Impact of epoxy glue curing time on the quality of overcoring stress measurements in low-temperature environments

Abstract : Many techniques of stress measurement or stress monitoring are based on the principle of gluing a strain-measurement device on the wall of a pilot hole using an epoxy resin. The curing time needed for this epoxy glue to achieve full hardening is rarely put into questions. Here, we present an in situ study of the impact of curing time on the quality of overcoring stress measurements using CSIRO Hi cells. The tests were conducted in an argillite rock at a temperature of 12°C. We show that the conventional curing time (16 hours) is clearly insufficient in this context and leads to anomalous response in strain readings during both overcoring and biaxial tests, thus hindering stress determination. We claim that in low-temperature near-surface environments, much longer curing times may be needed in order to ensure good quality of stress measurements. Other possible strategies are discussed in the body of this paper.