Contents lists available at ScienceDirect International Journal of Rock Mechanics and Mining Sciences journal homepage: www.elsevier.com/locate/ijrmms Estimation of creep parameters of rock salt from uniaxial compression tests Aditya Singh ⁎ , Chandan Kumar, L. Gopi Kannan, K. Seshagiri Rao, Ramanathan Ayothiraman Dept. of Civil Engineering, Indian Institute of Technology Delhi, New Delhi 16, India ARTICLE INFO Keywords: Creep Rock salt Uniaxial compressive strength Maxwell model Hooke model ABSTRACT 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 extra- polated 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 10 18 Pa.sec. 1. Introduction An important property of rock salt is its time-dependent deforma- tion behaviour or creep, which is typically captured by performing creep tests in uniaxial or triaxial conditions at constant values of stress or strain at a particular temperature. The stress and temperature can be changed stepwise during the test in order to create phases with constant condition 1 . An idealized one-dimensional creep plot is commonly re- presented by the instantaneous elastic deformation followed by the sequence of specific time-dependent deformations i.e. the primary transient phase where the strain rate decreases with time and the steady-state creep where the strain rate remains constant followed by tertiary creep characterized by a rapidly accelerating strain rate to ul- timate fracture failure 2 . A number of widely differing intuitive creep models such as classical Norton's power law which is an approximation of the actual creep be- haviour to LUBBY2 model which is additive superposition of the tran- sient creep rate with time and a constant secondary creep rate 3 are available. These creep models are essentially based on out of a fit to the creep testing data and some of the well-known models are compiled by Cristescu and Hunsche 4 . Comparison of creep rheological model such as Hookean model, Newtonian model, St. Venant model, Maxwell model, Maxwell and Kelvin-Voigt model, Standard model, Burger's model with experimental response has been made by Aydan et al. 5 with discussing their merits and demerits. which led to considerable differences in the prediction obtained owing to the merits and demerits of each model described by Cristescu and Hunsche 4 . In laboratory creep tests are conducted by the use of two type of apparatus: one, the conventional cantilever type apparatus wherein the load level can easily be manually kept constant with time and the other, the load/displacement-con- trolled apparatus capable of applying constant load by a servo-con- trolled machine. Cantilever type apparatus has the restriction of the level of applicable load which depends on the length of cantilever arm as well as oscillation during the change in load step while the servo- controlled testing machine requires continuous monitoring of load and its automatic adjustment. In additional to the fact that a dedicated creep testing machine fully equipped is expensive, these creep tests involves each loading step ranging from few days to several months or even years. This may lead to delay in characterization of creep para- meters and thus the design and execution of projects involving creep related stability issues. Hence, there is great demand for assessment/ estimation of creep parameters of rocks using simple routine tests either through simple models or empirical equations. It is reported that the creep behaviour can very well be related even through simple quasi- https://doi.org/10.1016/j.ijrmms.2018.04.037 Received 7 April 2017; Received in revised form 17 April 2018; Accepted 29 April 2018 ⁎ Corresponding author. E-mail addresses: gr8adityasingh@gmail.com (A. Singh), chandan060812@gmail.com (C. Kumar), gopikannan_2000@yahoo.com (L.G. Kannan), raoks@civil.iitd.ac.in (K.S. Rao), araman@civil.iitd.ac.in (R. Ayothiraman). International Journal of Rock Mechanics and Mining Sciences 107 (2018) 243–248 Available online 30 May 2018 1365-1609/ © 2018 Elsevier Ltd. All rights reserved. T