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Creep behaviour analysis of thin spray-on liners

Güner, Doğukan
Thin Spray-on Liner (TSL) is a relatively thin (2–5 mm) and fast-setting liner material used by spraying onto rock surfaces to support underground excavations. Areal support materials that are sprayed onto the rock, such as shotcrete or liners, are able to generate support resistance at small rock deformations and can prevent underground rockfalls from happening in the first place. However, where large ground convergence occurs, the more flexible TSLs may provide superior support over the full range of rock deformations. In this study, the creep behaviour of two TSLs were determined in the laboratory environment. Under constant stress levels, strain-time behaviours of two TSLs were determined up to 2 months of the testing period. For this purpose, dogbone shape test samples were prepared with different curing times (1-2, 7, and 14 days) and were tested under 23 ± 2 °C laboratory conditions according to the ASTM standards. Four different constant stress levels (80%, 60%, 40%, and 20% of the tensile strength) were applied until rupture of the specimens. The resultant correlations are explained using inter-related equations to make a forecast about the service life of the material (creep rupture envelopes) were derived. The proposed correlations may offer an insight into both the effective permanent support time and the strain amount at the liner failure. Experimental data were used to construct viscoelastic and viscoplastic models. A good agreement was generally observed between the presented models and the experimental results.In addition, the developed constitutive stress-strain-time relations were introduced to finite element software ABAQUS with a new subroutine. After verification of the implemented subroutines, the support performance of the TSLs on the global stability in the underground openings has been investigated. As a result of this study, the creep behaviours of TSLs were investigated for the first time in the literature and it has been found that TSLs are extremely sensitive to creep behaviour. The effective block bearing time of TSL’s with different wedge dimension scenarios of underground excavations were determined. As a result of the numerical studies, performed in 4 different representative rock mass squeezing behaviours with different TSL application thicknesses, it was concluded that the effect of TSL on global stability was extremely small.