Laboratory examination of anisotropy in the foliation plane of metamorphic rocks

Mechanical testing and ultrasonic measurements were used to establish the properties of metamorphic rocks in different directions of the foliation plane. Tests were undertaken on 42 mm diameter specimens cored at right angles to the foliation of gneissic rocks from southwest Sweden. Ultrasonic and tensile testing was carried out in three diametral directions and the data for each direction were compared. Coefficients, failure load anisotropy and velocity anisotropy were obtained. An anisotropy coefficient of 3% was detected by ultrasonic measurements, while the Brazilian tests indicated 15%. The study has shown that an anisotropy coefficient of the foliation plane is present, albeit small.