Influence of structural anisotropy on creep of rocksalt from Simla Himalaya, India: An experimental approach

The influence of structural anisotropy on time-dependent deformation (creep) of rocksalt from Shali Formation (Precambrian), Himachal Pradesh, India was investigated to analyze the differential mobility of rocksalt body in nature. The effect of structural anisotropy (orientation of bedding planes) with respect to the compression axis on the compressive strength, yield strength, modulus of elasticity, failure strain and yield strain of rocksalt has been analyzed on cubic samples (5 x 5 x 5 cm(3)) to collect the basic input for the purpose of creep of rocksalt. Time-dependent compression of cubic samples perpendicular, parallel and oblique to bedding planes were subjected to constant stresses equal to 30%, 40%, 50%, 60%, 70%, 75%, and 80% of their uniaxial compressive strengths for presenting analogous situation of variable stressing of rocksalt caused by over laying rocks and tectonic stresses. The results of experimental deformation reveal the strong control of structural anisotropy on development of instantaneous strain, transient strain, steady-state strain and accelerated strain; however the influence of structural anisotropy on deformation of rocksalt decreases with increment in stress levels. At higher stress level creeps, the control of structural anisotropy on deformation became negligible. The progress of time-dependent deformation occurs due to evolution of minute tensile and shear crack arrays in proportions. At lower stress creep the development of tensile crack arrays and shear crack arrays is assisted by structural anisotropy. However, at higher stress levels the creep of rocksalt is facilitated by reduction in tensile crack arrays and domination of shear crack arrays, resulting in shearing where the anisotropic rocksalt exhibits isotropic behaviour. Thus the mobility of rocksalt bodies is dependent on characteristic of structural anisotropy and stress conditions. (C) 2008 Published by Elsevier Ltd.