| Summary: | 碩士 === 淡江大學 === 土木工程學系 === 84 === The shear strength of non-persistent jointed rocks is usually
estimated by superimposing the strengths of joints and rock
bridges. Due to the different stiffness, the peak strengths of
joints and rock bridge do not mobilize simultaneously. The
direct superposition approach could over-estimate the strength
of jointed rocks. A series test of non-persistent jointed rocks
molded by artificial material is performed by direct shear test.
The cases of persistence in this test program include 0 (intact
rock), 0.5, 0.8, and 1.0 (persistence joint). The percentage of
joint strength mobilized at the failure , called the
mobilization factor C, is then back-calculated from the test
results taken into account of deformabilities or strengths of
rock bridge and joints. Moreover, the predicted strength
considering the factor C is applied to sandstone.The main
conclusions of this study are drawn as follows. (1) The
mobilization factor C of joint strength increases as the joint
persistence increases. (2) The shear strength of jointed rocks
range between the lower and the upper strengths that obtained by
strength approach and by deformability approach, respectively.
(3) The C value is suggested as 1 when the normal stress is
lower than 1/5JCS. (4) The factor C obtained by the
deformability approach is more reasonable than the strength
approach. (5) The frictional force on joint planes reduces the
stress concentration of rock bridges. (6) The effect of the
additional confining stress on shear force plane is really
existing and the value equals 0.73 of the normal stress in this
research.
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