Isothermal Creep Behaviour Investigation of Thin Spray-on Liners

Rock supporting has a vital importance in longevity and sustainability of all underground openings. There are many types and forms of supporting systems available in the mining/tunneling industry. In the last decade, a new polymer-based surface support material, thin spray-on liner (TSL), has started to take place of conventional surface support materials. TSL is defined as generally cement, latex, polymer-based and also reactive or non-reactive, multi-component materials applied to the rock surface with a layer of few millimeter thickness. They have the advantages of low volume, rapid application and low operating cost. The majority of current TSLs are two-part polyurethane/polyuria or Portland cement based latex products that are mixed on site before spraying onto surfaces. They are now being considered for highly stressed, deep, rock bursting conditions as a reinforcement and retaining element together with bolts and screen. In this study, the creep behavior of a cement-based TSL was investigated. For this purpose, 7-day cured dogbone TSL specimens were tested under 23±2°C laboratory conditions. A range of dead weights (80, 60, 40, and 20 % of the tensile strength) were applied until the rupture of the specimens. As a result of this study, the time-dependent strain behavior of a TSL was presented for different constant load conditions. Moreover, a new equation was derived to estimate tensile failure time of the TSL for a given loading condition. If the tensile stress acting on the TSL is known, the effective permanent support time of the TSL can be estimated by the proposed relationship.