Abstract: A plane-strain apparatus is provided for testing soft rock and concrete specimens for failure under compression load in a direction generally along a central axis of the specimen. The specimen has first and second end surfaces, and four side surfaces, which form a generally rectangular prism cross-section configuration. The apparatus includes a bottom support plate supporting the first end surface, and a top plate for loading the second end surface. A frame surrounds the specimen and supports a pair of diametrically opposite base wedge plates aligned with two opposite side surfaces of the specimen. The frame is spaced from the specimen and the base wedges and mating adjustable wedge plates which engage the opposite surfaces of the specimen facing the base wedge plates. The cylindrical frame, and the base wedges and mating adjustment wedge plates restrain movement of the opposite side surfaces of the specimen to be tested in first lateral directions perpendicular to the axis of loading.

Abstract: A compression test apparatus for geomaterial, such as rock or concrete, samples that is designed to provide measurements of a stress displacement characteristics of the failure zone. A geomaterial formed into a specimen comprising a right rectangular prism is supported by walls along two parallel faces and a back face. An axial load is kinematically applied by a plate that is suitably guided for movement against the specimen which is supported on bottom support plate. All of the surfaces in contact with the specimen are lined with hardened and polished steel plates and lubricated to minimize friction. The assembly of the specimen and its supports is in a conventional loading frame so that an axial load can be applied to one end of the specimen and reacted against the bottom plate. Displacement transducers monitor the lateral displacement of an unrestrained side surface of the specimen.