Failure Mechanisms and Strength of Non-Persistent Rock Joints
Mughieda, Omer Sulieman
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https://hdl.handle.net/2142/83445
Description
Title
Failure Mechanisms and Strength of Non-Persistent Rock Joints
Author(s)
Mughieda, Omer Sulieman
Issue Date
1997
Doctoral Committee Chair(s)
E. Cording
Department of Study
Civil Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
Jennings method which assumes full shear strength along joint and rock bridge is a useful reference condition. The Bridge Mobilized Strength Ratio, BMSR, provides a means of assessing how much of the reference strength along the bridge is mobilized. The MBSR is the ratio of (mobilized shear strength minus shear strength of joint) to (Jennings shear strength minus shear strength of joint), for the average normalized stress at failure. Conditions causing BMSR to be different from the reference value include: (a) for mode 1, shear failure in the plane of the joints through bridge and non-persistent joints, BMSR decreases, as the ratio of normal stress, $\sigma\sb{\rm n}$, to compressive strength, $\sigma\sb{\rm n}$/$\sigma\sb{\rm c}$, decreases below 0.2. (b) for mass stiffness $<$ bridge stiffness, and as number of bridges increases, progressive failure can develop reducing BMSR. (c) for the case of $\phi\sb{\rm j} \ll \phi\sb{\rm i}$, it was observed for single joints that the BMSR was above one. It is concluded that the higher value was due to concentration of the normal stress on the stiffer bridge, thus giving a higher shear strength than computed by Jennings method, which assumes a uniform normal stress distribution. (d) offset of joints reduces confinement and increases tensile stress conditions between joint segments causing a reduction of strength.
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