Abstract
Failure criteria of rock mass is the most important base for designing of surface and underground structures. However, behavior of jointed rock mass and its failure criteria are the controversial subjects of rock mechanics. Main reasons for this discussion are problems during or after the geotechnical application. However, some of the experimental and theoretical approaches are often preferred as they are practical, compatible with engineering considerations, and assist in decision-making process. On the other hand, the differentiation in the scale of the geosystem, which varies depending on the scale of geotechnical application, building process, and time, means that the failure conditions will also change. It is clear that the Mohr-Coulomb failure criterion, which is widely used in practice, cannot exactly represent discontinuous geo-environments (fractured rock) consisting of joint systems. Since the rock generally has a discontinuous character, it has been researched since the 1970s, and the Hoek-Brown failure criterion, put forth in the 1980s and modified many times until today, is widely accepted in application. Nevertheless, it is known that the empirical parameters used in this failure criteria proposed for different types of rocks are also open to discussion. In this paper, the results of the mechanical tests conducted on the previously-fissured model material, which is physically similar to rock mass are discussed. Marble samples whose grain boundaries were disturbed by cyclic thermal treatment were used as the model material. Post-failure curves of model material obtained from continuous failure state triaxial tests were compared with Hoek-Brown Failure Criteria. In conclusion, it was shown that the failure envelopes representing intergranular failure in the post-failure phase were similar and comparable to the Hoek-Brown Failure Criterion. However, it is found out that the post-failure strength in low confining stress may be lower than that of estimation by the Hoek-Brown criterion. Experimental studies have also shown that intergranular failure will develop among structural weaknesses in rock masses, and therefore the strength parameters commonly used in practice will depend on the size of geo-application.
Highlights
Research carried out excluding macro structures such as faults and bends demonstrate that the rock mass strength and behaviour is controlled, in short term, by both material and discontinuity properties and current researches focused on this phenomenon
Experimental studies have shown that intergranular failure will develop among structural weaknesses in rock masses, and the strength parameters commonly used in practice will depend on the size of geo-application
In stress-strain curves in Figure 4a, the first phase of the test until the point of failure is shown with thin and continuous lines. After this point, during in continuous failure state, confining pressure was regularly increased until 5 MPa, which is shown with dotted lines
Summary
Research carried out excluding macro structures such as faults and bends demonstrate that the rock mass strength and behaviour is controlled, in short term, by both material and discontinuity properties and current researches focused on this phenomenon. The strength and failure of rock can be determined by stress, energy and deformation criteria. Under dynamic and repeated stress, the strength parameters of rock masses change as is the case in other solid materials. The rate of deformation is known to have an impact on such cases. Likewise, other factors such as discontinuities, temperature, Y. Saturation, fluid motion affect rock strength and failure modes [1]-[3] and [4]
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More From: Pamukkale University Journal of Engineering Sciences
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