This paper presents the results from a 5 year laboratory and in situ investigation into the cause of corrosivity of rock support systems in underground hard rock mines. Long term in situ monitoring of corrosion was complemented by controlled investigations in corrosion chambers. During site visits, samples of corroded support units were collected from several mines and subsequently analyzed using S.E.M. and photomicrography. A series of controlled experiments in the corrosion chambers qualified and quantified the influence of minerals and rock deposits on the corrosion rate of steel and rock support.
Despite great strides in the design and implementation of ground control systems, it has been difficult to eliminate ground falls. One quality control issue related to support is related to a reduction in support capacity over time due to corrosion of the reinforcement and surface support units. This is illustrated in Figure 1. A corroded wire mesh failed and therefore, it no longer provided the support for which it was designed for. The reduction in support capacity due to corrosion may not be explicitly considered in the selection and design of an underground support system, as demonstrated by Figure 1. Quite often, corrosivity is found to be the issue during an investigation in the mechanisms and cause of failure that may have resulted in a fall of ground. Usually the investigation puts an emphasis on fracture analysis, and in doing so, this may identify the contribution of corrosion to a unit or system failure, . Fracture analysis focuses on the separation of a solid body into two or more parts under the action of stress. The stress would have initiated and propagated the formation of cracks. A ductile fracture mechanism is characterized by considerable plastic deformation prior to and during propagation of the crack.