Anisotropy of Rocks and Effect of Water Absorption

Abstract

The deformation and movement developed by the geological structure in some regions yield faults, fractures, folds and so on. Teref ore approach to the strength properties of rock mass is led by the understanding of the orientations of strength anisotropy of rocks due to these geological structures.In this paper the authors described the result of an experimental study on the change of strength and deformation characteristics with water absorption, taking their anisotropy into account. On the one hand tensile strength of rocks has been determined by the point load test on untrimmed test specimens to know the influence of water absorption to strength. On the other hand elastic wave velocities of specimens have been measured and the dynamic moduli Ed have been calculated in view of their deformation anisotropy.The tensile strength is denoted “σta” and “σtc” respectively in the direction normal and parallel to the discontinuity planes such as joint surfaces. Similarly the dynamic modulus in the direction normal to the discontinuity planes is called “Eda” and that parallel to them “Ede”.The results obtained as to the dynamic modulus and point load test are summarized as follows:-(1) Degree of strength anisotropy shown by point load test, “σta/σtc” and that by dynamic modulus, “Eda/Edo” correlate nearly with a straight line.(2) While degree of anisotropy of dynamic modulus “Eda/Edc” is decreased, that of strength anisotropy “σta/σtc” is increased when water is taken into discontinuity planes.