Hydrogeochemical modelling of corrosive environment contributing to premature failure of anchor bolts in underground coal mines

Anchor bolts are commonly used throughout underground mining and tunnelling operations to improve roof stability. However, premature failures of anchor bolts are significant safety risks in underground excavations around the world due to susceptible bolt materials, a moist and corrosive environment and tensile stress. In this paper, laboratory experiments and hydrogeochemical models were combined to investigate anchor bolt corrosion and failure associated with aqueous environments in underground coal mines. Experimental data and collated mine water chemistry data were used to simulate bolt corrosion reactions with groundwater and rock materials with the PHREEQC code. A series of models quantified reactions involving iron and carbon under aerobic and anaerobic conditions in comparison with ion, pH and pE trends in experimental data. The models showed that corrosion processes are inhibited by some natural environmental factors, because dissolved oxygen would cause more iron from the bolts to oxidize into solution. These interdisciplinary insights into corrosion failure of underground anchor bolts confirm that environmental factors are important contributors to stress corrosion cracking.