ABSTRACT:

To carry out the proposed research work, some molds were designed. The molds were used to fabricate specimens possessing two perpendicular joints making angles of 0, 15, 30, 45, 60, 75 and 90 degree to the longitudinal axis. The specimens were prepared out of suitable proportion of plaster. The jointed and intact specimens were subjected to triaxial testing at various confining pressures. The degree of Anisotropic Effect induced in the specimens due to the jointing and their inclinations under the effect of confining pressures were investigated. The studies were undertaken considering the definition; Ae=(sia-s ja )/ sia where 'Ae' is the Anisotropic Effect, sia is the peak axial strength of the intact specimen under the 'a' confining pressure, s ja is the peak axial strength of the jointed specimen under the 'a' confining pressure. The behavior of anisotropic specimens was also investigated with regard to confining pressure and the jointing inclinations in order to assess the failure mechanism.

1. INTRODUCTION

Discontinuities are one of the most important phenomena that cause the mechanical anisotropic in rocks. This mechanical anisotropy would, in turn, impose reduction of strength. Therefore, the discontinuities and degree of their influence on the rocks must be studied carefully in order to define the rocks behavior. The confining pressure, on the other hand, is an important parameter that controls the percentage effect of the rock discontinuities on the rock strength with respect to the intact rock strength. Basically, the strength of the intact rocks is governed by the geological, lithological, physical, and environmental characteristics affecting the rocks. The volcanic rocks in the nature, as compared to the sedimentary and metamorphic rocks possess a higher degree of anisotropy, but due to the high amount of the jointing exhibit anisotropic behavior. It has been tried to study and evaluate the effect of the confining pressures on the degree of Anisotropic Effect in this research work.

2. LITRATURE SURVAY ON THE BAHAVRIOUR OF THE ANISOTROPIC ROCKS

Initial comprehensive studies on the characteristics of anisotropic and bedded rocks were performed by Muller in the year 1930. His works were based on the elastic, deformability and strength properties of the anisotropic rocks under uniaxial loading conditions. Muller performed his researches on cubic and cylindrical specimens of Sandstones, Sandy Shale, Clayey Shale and some samples of Coal. The samples were subjected to uniaxial loading perpendicular and parallel to their beddings. He observed the maximum anisotropic strength in the Clayey Shale. The average strength on the samples loaded parallel to beddings were 68% with respect to the samples loaded perpendicular to their beddings. The tests performed on the Sandstones also demonstrated the same results, but the modulus measured while loading parallel to the beddings was 1.23 times to compare with loading perpendicular to beddings. The first empirical research on the anisotropic strength of metamorphic rocks was conducted by Lapper in the year 1949. Griggs and his coworkers (1951), performed tests on four rock samples under the various loading and temperature conditions and, thus studied the mechanical and structural properties of the Marble rocks.

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