Static and Dynamic Elastic Modulus of Jointed Rock Mass: Influence of Joint Frequency, Joint Inclination and Joint Factor

Static and Dynamic Elastic Modulus of Jointed Rock Mass: Influence of Joint Frequency, Joint Inclination and Joint Factor

T. G. Sitharam (Indian Institute of Science, India), M. Ramulu (Central Mining Research Institute, India) and V. B. Maji (Indian Institute of Technology, India)
Copyright: © 2010 |Pages: 24
DOI: 10.4018/jgee.2010070107

Abstract

In this paper the compressive strength/elastic modulus of the jointed rock mass was estimated as a function of intact rock strength/modulus and joint factor. The joint factor reflects the combined effect of joint frequency, joint inclination and joint strength. Therefore, having known the intact rock properties and the joint factor, jointed rock properties can be estimated. The test results indicated that the rock mass strength decreases with an increase in the joint frequency and a sharp transition was observed from brittle to ductile behaviour with an increase in the number of joints. It was also found that the rocks with planar anisotropy exhibit the highest strength in the direction perpendicular to the anisotropy and the lowest at an inclination of 30o-45o in jointed samples. The anisotropy of the specimen influences the dynamic elastic modulus more than the static elastic modulus. The results were also compared well with the published works of different authors for different type of rocks.
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2. Model Material

Laboratory tests were conducted on cylindrical specimen of Plaster of Paris (POP). Because of the ease of casting, flexibility, quick hardening and low cost, POP was selected as a model material. The behaviour of hardened POP is similar to the behaviour of a soft rock. Specimens of 38mm in diameter and 76mm in height were prepared for uniaxial and triaxial compression tests, conducted at different confining pressures. Tests to determine the composition and texture of POP X-ray diffraction study has been done. X-Ray diffraction shows that POP used here contains mostly bassanite (CaSO4 0.5H20) and gypsum (CaSO4 2H20).

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