Direct tensile behavior of a transversely isotropic rock

The tensile behavior of a transversely isotropic rock is investigated by a series of direct tensile tests on cylindrical argillite specimens. To study the deformability of argillite under tension, two components of an electrically resistant type of strain gage with a parallel arrangement, or a semiconductor strain gage, are adopted for measuring the small transverse strain observed on specimens during testing. The curves of axial stress vs axial strain and vs average volumetric strain ape presented for argillite specimens with differently inclined angles of foliation. Experimental results indicate that the stress-strain behavior depends on the foliation inclination of specimens with respect to the loading direction. The five elastic constants of argillite are calculated by measuring two cylindrical specimens in the manner recommended by Wei and Hudson. Based on theoretical analysis results, the range of the foliation inclination of the specimens tested is investigated for feasibility obtaining the Jive elastic moduli. A dipping angle of the foliations (theta) of 30-60 degrees with respect to the plane normal to the loading direction is recommended. The final failure modes of the specimens are investigated in detail. A sawtoothed failure plane occurs for the specimens with a high inclination of foliation with respect to the plane perpendicular to the loading direction. On the other hand, a smooth plane occurs along the foliation for specimens with low inclination of foliation with respect to the plane normal to the loading direction. A conceptual failure criterion of tensile strength is proposed for specimens with a high inclination of foliation. (C) 1997 Elsevier Science Ltd.