Investigation into durability degradation and fracture of cable bolts through laboratorial tests and hydrogeochemical modelling in underground conditions

Premature failures of cable bolts caused by durability degradation in underground reinforcement systems have been more and more often observed. To identify various factors affecting the corrosion process, the corrosion processes were examined through laboratorial testing programs as well as hydrogeochemical modelling. Experiments were carried out in simulated underground conditions in “corrosion cells” containing stressed cable bolt specimens as well as groundwater, clay, coal or a combination of the materials. Water chemistry and corrosion pattern analysis of specimens in different testing conditions were conducted. Hydrogeochemical models were established and the formation of corrosion products, the change of ion concentration and factors related to corrosion rates were studied. The results showed the corrosion degree of specimens could be classified into three categories. The dissolved oxygen was the main factor affecting the general corrosion and stress level, pH and electrical conductivity were secondary factors. Erosive ions were main factors affecting localised corrosion which was mainly observed to form at high stress areas. A ‘staple’ like crack initiated at localised corrosion were observed which was identified as a potential site for stress corrosion cracking. The modelling results showed sulphide iron generated in presence of microorganisms which would also accelerate stress corrosion of specimens. The obtained results and proposed methodologies would establish quantifiable data to compare variable mine conditions and help understand the corrosion mechanisms in underground conditions.