Rock failure under the confined Brazilian test

Abstract

The Brazilian, or indirect tensile, test, in which a disk is loaded in a diametral plane by forces applied at opposite ends of a diameter, is extended by jacketing the specimen and applying an additional confining pressure. In this way failure may be studied over a range of conditions in which the least principal stress varies from tensile to compressive. The fracture is always an extension fracture in the loaded diametral plane, even if all principal stresses are compressive. The stress analysis is based on elastic strain theory. Experiments were made on three rock types, and they suggest that the value of the intermediate principal stress affects the conditions for failure. This effect is of the same order of magnitude as that shown by experiments on hollow cylinders with axial loading and external confining pressure.

An Experimental Study of Dynamic Tensile Failure of Rocks Subjected to Hydrostatic Confinement

“…8b, c,d,e are 43.81,48.22,51.63,and 59.74 MPa,respectively. From the comparison among the CT images, it is obvious that the fracture is tensile in the loaded diametral plane, regardless of the levels of the confinement and the loading rate, which is the same as reported by Jaeger and Hoskins (1966). The fracture is more obvious when the rocks are under 10 MPa confinement (Fig.…”

“…However, the dynamic tensile strength of the one under 20 MPa hydrostatic confinement is 56.37 MPa, which is only 6.37 MPa higher than the former. This decrease of the increment is also observed for rocks tested statically and dynamically under confinement in the literature (Jaeger and Hoskins 1966;Lindholm et al 1974).…”

“…They concluded that the dynamic tensile strength of rock materials decreases with the increase of the static pre-tension. Jaeger and Hoskins (1966) studied static tensile failure of confined rocks, which also presents an increase in strength with the confining pressure. However, a comprehensive study is needed to examine the dynamic tensile failure of hydrostatically confined rocks, which is the objective of the current work.…”

Propagation of fractures from an interface in a Brazilian test specimen

“…The extension fracture is then postulated to form when wedges are forced into the disc. Jaeger and Hoskins [9] stated, however, that the formation of wedges cannot be the primary means of failure as the wedges are not observed in every case. Their experimental evidence indicates that failure begins as an extension fracture at the centre and propagates to the surface.…”

Superposition of Stress Fields in Diametrically Compressed Cylinders

“…Li and Wong (2013) show the evolution of the state of art about the subject, analysing the 43 most important works, in the view of the authors, from 1943-2011. The papers most directly related to this article are: Sheep (1943), Hondros (1959), Colback (1966), Jaeger and Hoskins (1966), Jaeger (1967), Hudson et al (1972), Wijk (1978), Yanagidani et al (1978), Sundaram and Corrales (1980), Yu et al (2006) and Markides et al (2010Markides et al ( , 2011. These publications were critically examined, but did not reveal any references to the aspects emphasised here.…”