A series of uniaxial compressive strength tests were performed to study the deformation characteristics of bedded sandstone with bedding layers in different orientations. Test results revealed that the samples with bedding layers oriented in smaller angles (55°, 35°, 20°, and 10°), measured from the horizontal axis, undergo larger deformations compared to that of the samples with bedding layers oriented in higher angles (83°) at any stage of loading. When 75% of the peak load is reached, a considerable deformation had taken place in samples with bedding layers oriented in smaller angles (55°, 35°, 20°, and 10°), whereas a significantly less deformation had taken place in samples with bedding layers oriented in higher angles (83°). Moreover, at 55° and 35° bedding orientations, deformation was mainly observed within the middle region of specimens and at 20° and 10° bedding orientations deformation was more diffused throughout the specimen.
Understanding the mechanical response of rock upon loading is of central importance in many rock mechanics and rock engineering applications such as open-pit slope stability analyses, tunnel designs and underground explorations. Deformation characteristics of rocks are highly variable across different types and different geological settings of rock. Laboratory scale studies have been extensively used to investigate the deformation behavior of different rock types.
The role of micro-fracturing for rock deformation is an established concept that describes micro-fracturing events begins at low stresses (below the peak stress) and they further propagate with increasing stress until the macro-scale failure takes place (Scholz 1970, Hardy 1972, Wu & Thomsen 1975 and Boutt & McPherson 2002). Walsh & Brace (1973) explains that the rock deformation is a complex process in which compaction due to the crushing of pores competes with dilatancy due to the growth of cracks. Microcracks can be developed in any part of a loaded rock sample, however, only some of them will coalesce and contribute to the final macro-scale fractures at the failure. Identifying these micro-crack development characteristics and their coalescence behavior is extremely important in characterizing the rock mechanical behavior.
