Estimation of creep parameters of rock salt from uniaxial compression tests

This paper discusses an approach to predict the creep behaviour of rock salt using uniaxial compression testing machine, as the conventional creep testing equipments are expensive and scarcely available. As commonly observed in brittle rock, a distinct Kaiser effect is not found during pre-peak loading path, but after unloading a distinct Kaiser effect is observed in rock salt. In the present study, Acoustic Emissions (AE) technique is used to infer the rock salt behaviour under uniaxial compression. The AE technique used in the present study to explain the rock salt behaviour is based on a combination of Maxwell and Hooke models. Using these models, elastic and viscous parameters are calculated. The proposed model is able to predict the stress-strain response of rock salt with a fair accuracy in both loading and unloading conditions. It is observed that the viscosity has negative correlation with the strain rate and hence the calculated viscous parameters are then extrapolated. The extrapolated results of viscosity for different strain rate in the range of 10− 6.5-10− 10 s-1 are very close with reported values from the literature and for the strain rate below 10− 10 s-1, the predictions are higher than the values reported in literature. This is due the fact that below 10− 12 s-1 strain rate, the viscosity becomes independent of the strain rate and its value becomes almost constant for 3-5 mm grain size rock salt. Hence a cutoff viscosity is proposed at a value of 1018 Pa.sec.