The strength and dilation of rock joints in the field cannot be evaluated solely on the basis of parameters scaled from laboratory data but also requires assessment of large-scale irregularities not present in the lab sample. A constitutive model for rock joints has been developed that considers the dilation and strength along both small-scale joint roughness scaled from laboratory data, and field-scale waviness determined from geologic observations. The model also considers the effect of strength loss along joint as a result of joint opening during unloading. The model has been incorporated in 3DEC using the built-in subroutine language, FISH, and has been used to represent the behavior of the rock ridge carrying a major roadway through a quarry in the greater Chicago, Illinois area.; The degradation in dilation and post-peak strength along irregularities is modeled using the plastic work done in shear. A dimensionless product of plastic work, rock strength, and wavelength of irregularities has been developed which fits the direct shear test results. An approach to scaling shear strength and shear displacement from laboratory to in the field is suggested. Analyses are correlated with shear displacements on the roadway and inclinometer readings measured in the rock ridge.
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