Stability, Failure, and Measurements of Boreholes and Other Circular Openings (1993) / Chapter Skim
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Introduction
Introduction
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This may be due to the emergence of new challenges, such as completing deviated boreholes, together with an upgrading of knowledge on rock mass behavior and analysis methodologies. The fundamental developments for understanding the environment around a deep wellbore were established by Westergaard ~ 1940, who predicted the existence of a plastic state around the wellbore, based on Terzaghi's effective stress concept.
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In addition to the results inferred from the analysis of the formation response to the introduced stress concentration field, modern investigators have the option of perfonning various other tests in the borehole, including dilatometer or jacking tests, micro- and mini-hydraulic fracturing tests, and fluid extraction; providing further means for the investigation of fluid chemistry, formation properties, and state of Tress. The stability of circular openings can be considered by separating the potential rock failure mechanisms into four categories: (1)
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For example, for a pure mathematician/numerist, failure usually means that the material starts e~enencing some plastic yielding. At the other end of the spectrum, an experimentalist might define failure as the stage where the failed zone has reached the external boundaries of the rock sample.
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, although the numerical models predicted total collapse. When this occurs in practice, engineers usually invoke poorly developed concepts, such as progressive rupture, scale effects, stress gradient effects, or even plastic adaptation.
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